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Regioisomerism vs Conformation: Impact of Molecular Design on
the Emission Pathway in Organic Light-Emitting Device Emitters
Prasannamani Govindharaj, Aleksandra J. Wierzba, Karolina Kęska, Michał Andrzej Kochman,
Gabriela Wiosna-Sałyga, Adam Kubas,*Przemysław Data,*and Marcin Lindner*
Cite This: https://doi.org/10.1021/acsami.3c19212
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sı Supporting Information
ABSTRACT: Despite the design and proposal of several new
structural motifs as thermally activated delayed fluorescent
(TADF) emitters for organic light-emitting device (OLED)
applications, the nature of their interaction with the host matrix
in the emissive layer of the device and their influence on observed
photophysical outputs remain unclear. To address this issue, we
present, for the first time, the use of up to four regioisomers
bearing a donor−acceptor−donor electronic structure based on the
desymmetrized naphthalene benzimidazole scaold, equipped with
various electron-donating units and possessing distinguished
conformational lability. Quantum chemical calculations allow us
to identify the most favorable conformations adopted by the
electron-rich groups across the entire pool of regioisomers. These
conformations were then compared with conformational changes caused by the interaction of the emitter with the Zeonex and 4,4′-
bis(N-carbazolyl)-1,1′-biphenyl (CBP) matrices, and the correlation with observed photophysics was monitored by UV−vis
absorption and steady-state photoluminescence spectra, combined with time-resolved spectroscopic techniques. Importantly, a CBP
matrix was found to have a significant impact on the conformational change of regioisomers, leading to unique TADF emission
mechanisms that encompass dual emission and inversion of the singlet−triplet excited-state energies and result in the enhancement
of TADF eciency. As a proof of concept, regioisomers with optimal donor positions were utilized to fabricate an OLED, revealing,
with the best-performing dye, an external quantum emission of 11.6%, accompanied by remarkable luminance (28,000 cd/m2).
These observations lay the groundwork for a better understanding of the role of the host matrix. In the long term, this new
knowledge can lead to predicting the influence of the host matrix and adopting the structure of the emitter in a way that allows the
development of highly ecient and ecient OLEDs.
KEYWORDS: TADF, RTP, S-T inversion, regioisomerism, OLED, TICT, charge transfer
1. INTRODUCTION
In recent years, a tremendous growth of research toward
luminescent display and lighting technologies based on organic
light-emitting devices (OLEDs)
1
has been motivated by their
low production costs, ease of processing, superior color purity,
and performance.
2,3
Additionally, OLEDs have provided a
significant platform in photodynamic therapy,
4,5
sensing
technologies,
6
and wearable electronics,
7
among other
applications.
8
In this context, organic molecules that exhibit
a phenomenon of thermally activated delayed fluorescence
(TADF) can revolutionize the domain of OLED emitters as
they are capable of harvesting both singlet and triplet excitons,
giving, theoretically, 100% of internal quantum eciency
(IQE).
9
When the energy dierence between the singlet−
triplet excited states (ΔEST) is suciently small and spin−orbit
coupling (SOC) is nonzero, triplet excitons can transition back
to the singlet energy level through thermally activated reverse
intersystem crossing (RISC). After the singlet energy level is
populated, triplet excitons eciently relax to the ground state.
Therefore, there has been swift progress in the development of
molecular engineering aimed at narrowing the ΔEST energy
gap.
10−16
To realize this scenario, variable donor−acceptor−
donor (D−A−D) architectures have been examined as their
twisted electron-rich moieties can increase the dihedral
angle(s) between D−A units. The implementation of such
electronic structures provokes intermolecular charge transfer,
for which second-order spin-vibronic SOC promotes ecient
RISC. Under these circumstances, the role of regioisomers can
be vitally important for the properties of the singlet and triplet
Received: December 22, 2023
Revised: April 14, 2024
Accepted: April 17, 2024
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https://doi.org/10.1021/acsami.3c19212
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excited states.
17−19
Such minimal structural changes (without
any modifications of functional groups) also underscore the
impact of the topology of the π-conjugated scaold on the
mechanism of emission, the eciency of electroluminescence,
and stability under the current applied. The development of
regioisomers to enhance TADF functionalities is still in
progress and is limited to a select few structural frameworks.
Among the systems revealed so far, Monkman and co-
workers
20
reported on 2,8- and 3,7-bis(10H-phenothiazin-10-
yl)dibenzo[b,d]thiophene-S,S-dioxide, for which ecient
TADF via spin-vibronic coupling was noticed (2,8-DPTZ-
DBTO2) with a maximum external quantum emission of
(EQEmax) of 7%, whereas TADF was not observed for its 3,7-
DPTZ-DBTO2counterpart, as marked in Figure 1a. The
groups of Ifor and Zysman-Colman shifted their focus from
small-molecule emitters
21
to the regioisomeric G2 and G3
dendrimers (Figure 1b) to assess their suitability as solution-
processed, host-free, TADF OLED emitters.
22,23
In this
context, the tris(phenyl)triazine core was branched with
multiple [bis(3,6-ditBucarbazole)Cz] units at either one
(tBuCz2 mTRZ) or two (tBuCz4 mTRZ) meta-positions of
the phenylene linker. Comparative studies with the previously
reported para-decorated analogue (tBuCz3pTRZ)
24
revealed
the superiority of asymmetric units. This superiority was
evident in the remarkable OLED performance achieved using
tBuCz2 mTRZ (EQEmax = 19.9%) as well as tBuCz4 mTRZ
(EQEmax = 23.8%) as emitting systems. This correlation was
rationalized by better control over the reorganization energies,
leading to an enhancement of the RISC process. The impact of
the substitution pattern on the photophysics of TADF emitters
was also faced by Takeda and Data, who put an emphasis on
macrocyclic emitters with a structure composed of DBPHZ
and diphenyl amines, forming a saddle-like structure. As
demonstrated in Figure 1c, their phenylene linkers were
bridged in the para (p-1 DBPHZ)
25
and meta (m-1 DBPHZ)
26
positions to provide topological isomers. The comparison of
their physicochemical properties disclosed a larger bending
angle (and thus a shorter distance between amine and the A-
unit) for m-1 DBPHZ. This was reflected in an increased ΔEST
= 0.31 eV and much weaker TADF emission with respect to
the para (p-1 DBPHZ) versus the meta (m-1 DBPHZ). The
latter entity showed a narrow energy gap (ΔEST = 0.18 eV),
leading to light production in the TADF OLED (λEL = 605
nm; EQEmax = 6.9%). Very recently, Hazra and co-workers
27
reported on the examination of the 3-fold isomers (ortho/
meta/para) of the well-established dicyanobenzene scaold
Figure 1. (a−d) Molecular structures of selected regioisomeric emitters with respect to their emissive behaviors (pictures in (d) represent the color
of the emission). The structures (a) and (b) were reproduced with permission from ref 20 (copyright 2017, Nature Portfolio) and ref 22 (copyright
2022, Wiley-VCH), respectively. The first structure in (c) was reproduced from ref 25 (copyright 2020, American Chemical Society) and the
second one was reproduced with permission from ref 26 (copyright 2020, Wiley-VCH). Structures in (d) were adapted from ref 27, available under
a CC-BY-NC license, copyright 2023, Hazra et al. (e) General structure of regioisomeric emitters based on bis-substituted NBIs (with four dierent
variants: 3/4/11/10) (green represents isolated isomers, while gray represents those that were not isolated in a pure form). Curved arrows point
out the impact of the specific position on the observed photophysical phenomenon. For the sake of clarity, D1 and D2 are denoted as donors, while
A is the acceptor.
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decorated with diphenylamine moieties. This investigation
revealed significant variations not only in the ΔEST energy but
also in distinct behaviors in the crystalline phase, resulting in
distinguishable mechanoluminescence that ranged from green
to orange emission exclusively for ortho isomers, which is
attributed to its crystallization in the centrosymmetric P21/C
space group. Consequently, there is a need for studies that
would explore the relationship between even higher-order
regioisomers (four dierent positions) and their photophysical
properties, which can indeed be aected by the host matrix.
Nonetheless, such a conceptually new molecular design has not
yet been identified and investigated in the context of TADF
emitters and their use in the OLEDs.
Thus, to lay their foundations, herein we demonstrate how
the solid-state matrix can aect the molecular conformation of
TADF emitters using the example of up to four regioisomers
with a D−A−D electronic structure. A correlation between the
occupied positions of donors and their photophysical output
reveals unique emissive behaviors, manifested by enhanced
TADF, dual emission, and inversion of singlet−triplet excited
states energy levels, as underpinned in Figure 1e. As clear
evidence, regioisomers were further explored for OLED
applications as TADF emitters, showing that these optimal
donor positions exhibited an EQE as high as 11.6% with a
remarkable luminance of 28,000 cd/m2, while suboptimal
regioisomers disclosed undesired aggregation and room-
temperature phosphorescence (RTP).
2. RESULTS AND DISCUSSION
2.1. Synthesis. To study the TADF phenomenon, in the
solid state, with higher-order regioisomers, the naphthalene
benzimidazole (NBI) scaold can be conceived as the ideal
molecular candidate and is envisioned to have a high degree of
symmetry. Building on that, we designed and synthesized a bis-
substituted NBI which can be functionalized with various
electron-rich amines and form four isomers with the D−A−D
electronic structure (Figure 1e). Along this line, we
successfully synthesized and isolated the entire set of
phenoxazine-based (PXZ) D−A−D compounds (53.1-4);
three out of the four were obtained for 9,9′-dimethylacridine
(DMAc, 55.1 and 55.3-4) and 3,6-ditertbutyl-carbazole
(tBuCz) derivatives (56.2-4), and two out of the four were
obtained for the iminodibenzyl (IDB) family (55.1 and 55.4).
All of the obtained dyes were subsequently investigated for
their photophysical and electroluminescent behaviors, theoret-
ically and experimentally. The detailed synthetic process for
D−A−D emitters decorated with electron-rich moieties
(including PXZ, DMAC, tBuCz, and IDB) in positions 3,11,
4,11, 3,10, and 4,10-NBI is outlined in Scheme S1 (Supporting
Information). The regioisomeric emitters were assembled
within two scalable synthetic steps comprising acid-catalyzed
condensation of 4-bromo naphthalene imide and 3-bromo-1,2-
diaminobenzene, followed by Buchwald−Hartwig amination
with electron-rich moieties. A mixture of isomers were isolated
via common silica gel column chromatographic separation and
characterized by a combination of 1H, 13C, and 2D NMR
spectroscopies along with high-resolution mass spectrometry
(ESI), which helped to unambiguously confirm the identity
Figure 2. (I) DFT-optimized conformation of selected dyes manifested by marked dihedral angles (a−d); (II) EDDMs for the lowest few singlets
and the triplet of compound 53.1 in the D1-a, D2-a conformation. The EDDMs are plotted in the form of isosurfaces with isovalues of ±0.0025 e/
a03. The red and blue isosurfaces delimit regions in which the electron density is increased and decreased, respectively, relative to the ground state.
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and purity of the obtained dyes. For the sake of clarity, we
combined and displayed the structures of all isolated isomers as
well as these four, which were obtained as a mixture of isomers,
in Supporting Information (Figure S22).
2.2. Electronic Structure Calculations. Recent computa-
tional research has revealed the significant impact of
conformational motion, particularly in the electron-rich units
of TADF emitters.
28−31
This motion, characterized by the
distribution of the dihedral angle,
32,33
plays a crucial role in
influencing both the S−T energy gap and the oscillator
strength. This is essential for establishing a high radiative decay
of the delayed fluorescence (DF) emission. In light of these
considerations, our studies began with the implementation of
density functional theory (DFT) calculations to identify
predominant conformation preferences across a set of
regioisomeric emitters. For the sake of convenience, we
conducted these calculations using two representative series
of molecules, namely, 53.1-4and 55.1-4, whose structures are
illustrated in Figure 2. As each of the fluorophores under study
has two identical electron-donating moieties (one at position
11 or 10, and another either at position 4 or 3), we denote the
former moiety as D1 and the latter as D2. The fused 1,8-NBI
electron-accepting moiety is denoted as A(see Figure 2) for
the sake of clarity. In the ground electronic state of the 53.X
series, the PXZ electron-donating moieties D1 and D2 can
potentially adopt quasi-equatorial (eq) or quasi-axial (ax)
orientations with respect to the A moiety. Thus, each of these
compounds can potentially exist in four conformations arising
from the dierent orientations of the two electron-donating
moieties, i.e., D1-eq, D2-eq; D1-eq, D2-ax; D1-ax, D2-eq; and
D1-ax, D2-ax. Regarding the D1 moiety, geometry optimiza-
tions confirm the existence of minima on the potential energy
surface (PES) of the ground state that correspond to D1-eq
and D1-ax conformations. In the case of the D2 moiety,
however, we found that only a D2-ax conformation
corresponds to a minimum on the ground-state PES. Attempts
to optimize a D2-ax conformation result in the D2 moiety
relaxing spontaneously toward a quasi-equatorial conforma-
tion. The inability of the D2 moiety to adopt a quasi-axial
conformation is presumably due to steric interactions with the
Afragment. It must be thus stressed that each compound in
the 53.X series has only two stable conformations: D1-eq, D2-
eq and D1-ax, D2-eq (Figure 2a,b), which are manifested by
the corresponding dihedral angles to be 91.5 and 22.4°(for
D1, respectively) and −94.8 and −95°(analogously for D2).
Notably, the populations of the D1-ax, D2-eq conformers are
expected to be on the order of 0.01. As an illustration, Figure
2I shows the D1-eq, D2-eq and D1-ax, D2-eq conformers of
compound 53.1. For all four compounds in the 53.X series, the
D1-eq, D2-eq conformation is lower in energy than the D1-ax,
D2-eq conformation by around 20 kJ/mol. We therefore
conclude that the D1-eq, D2-eq conformation is the dominant
form of all four compounds.
In regard to the 56.X series, the Cz moieties are less bulky
than the PXZ moieties. Consequently, all compounds in this
series adopt equatorial-like conformations in which the Cz
moieties are slightly twisted with respect to the plane of the A
moiety. More specifically, each compound has two inequiva-
lent equatorial conformations that dier in the relative
orientation of the D1 and D2 moieties. For reference, the
two possible conformations of compound 56.2 are illustrated
in Figure 2I. In conformation I(Figure 2c), the D1 and D2
moieties are roughly coplanar (judging by their mutual
orientation), whereas in conformation II (Figure 2d), they
are roughly perpendicular. For each compound, the two
equatorial conformations lie very close in energy and are also
found to have similar electronic excitation spectra. This is
because the D1 and D2 moieties are separated from one
another by the intervening A moiety, and their orientation
relative to one another makes little dierence, as demonstrated
through the value of the corresponding dihedral angles (Figure
2c,d). In the solution phase, conformers Iand II are expected
to coexist in roughly equal abundances.
2.2.1. Electronic Excitation Spectra. Having investigated
the conformational preference of the 53.X and 56.X series of
compounds, we moved on to examine their electronic
excitation spectra. The main results of the calculations�the
vertical excitation energies and the electronic structures of the
low-lying excited states�are presented visually in Figure 2,II.
A more detailed breakdown of the vertical excitation spectrum
of each compound is reported in Table S1 and Figures S1 and
S2 (Supporting Information). For all four 53.X compounds in
this series, the lowest singlet excited state is found at an energy
of roughly 2.7−2.8 eV (the exact energy depends on the
specific compound in the series). This state arises from
intramolecular charge transfer (ICT) from the D2 moiety onto
the 1,8-NBI-like fragment of the A moiety (D2 →A1ICT). As
an illustration of the electronic structure of the D2 →A1 ICT
state of each compound, Figure 2 shows plots of the electron
density dierence maps (EDDMs). The energy of the D2 →A
1ICT state is rather insensitive to the positions of electron-
donating moieties (D1 and D2) as the S0→S1vertical
excitation energies for all four compounds in 53.X fall within a
narrow energy range. The lack of sensitivity to the position of
the D1 moiety is to be expected as that moiety is not involved
in this ICT state. More surprising is the insensitivity of the
energy of the D2 →A1ICT state to the position of the D2
moiety. Intuitively, one would expect that the energy of an ICT
state should be sensitive to the geometry of the linkage
between the electron-donating and -accepting moieties, and
there are several examples in the literature where this is indeed
the case.
34,35
For this reason, we do not rule out the possibility
that the lack of sensitivity of the energy of the D2 →A1ICT to
the position of the D1 moiety is an artifact of the time-
dependent DFT (TDDFT) calculations. It would follow that
compounds in the 53.X series may dier from one another
substantially in terms of their photophysics. Another singlet
ICT state, which corresponds to a shift of electron density
from the D1 moiety onto the A moiety (D1 →A1ICT), is
found a few tenths of an electron Volt above the D2 →A1ICT
state. The energy of the D1 →A1ICT state is somewhat
sensitive to the position of the D1 group but not to the
position of the D2 group. The two low-energy ICT states of
the 53.X series of compounds exhibit very low oscillator
strengths. This is because of the quasi-equatorial orientations
of the D1 and D2 moieties�the occupied and virtual orbitals
involved in either ICT state show very little spatial overlap
with one another. Absorption by these ICT states may be
responsible for the broad, weak bands seen in the photo-
absorption spectra of the 53.X series in the range of around
450−550 nm (which corresponds to photon energies in the
range of around 2.2−2.8 eV). Moreover, for each compound in
the 53.X series, we find a bright 1ππ*-type excited state at an
energy of roughly 3.8 eV. This state is largely localized on the
A moiety. Accordingly, we denote it as the A 1ππ*state. The
vertical excitation energy into the A 1ππ*state is insensitive to
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the positions of the D1 and D2 moieties, which are not
involved in this state. The transition into this state gives rise to
intense photoabsorption bands of these compounds near 375
nm (which corresponds to a photon energy of around 3.3 eV).
Regarding the triplet states for each compound in the 53.X
series, the lowest triplet state is a 3ππ*-type state at an energy
of roughly 2.5 eV that is localized on the A moiety. Its energy is
insensitive to the positions of the D1 and D2 moieties. The
second-lowest triplet state of each compound is the triplet D2
→A3ICT state, located at an energy of roughly 2.7−2.8 eV.
As with its singlet counterpart, the energy of this state is
calculated to be insensitive to the positions of the D1 and D2
moieties. We now move on to the 56.X series of compounds in
which D1 and D2 are Cz moieties. The calculated vertical
excitation spectra are shown on the right side of Figure 2. The
full calculated results are relegated to Table S2 in the
Supporting Information. For the sake of brevity, we only
include the spectrum of conformer Iof each compound; the
spectrum of conformer II is very similar to that of conformer I.
Since Cz is a relatively weaker electron-donating moiety than
PXZ, in the 56.X series of compounds, the ICT states�both
singlet and triplet�are found to be higher in energy than those
in the 53.X series. Another important dierence is that in the
56.X series, both the D1 and D2 moieties adopt equatorial-like
orientations. As the D1 and D2 moieties are only slightly
skewed with respect to the plane of the A moiety, their π- and
π*-type orbitals overlap well with those of the A moiety.
Consequently, some of the D1 →A and D2 →A1ICT states
of the 56.X series of compounds have a substantial admixture
of 1ππ*character, and they exhibit high oscillator strengths for
excitation from the ground state. In each compound in the
56.X series, the lowest singlet excited state is the D2 →A1ICT
state, at an energy of roughly 3.4−3.5 eV (depending on the
specific compound in the series). Its energy is insensitive to the
position of the D1 and D2 moieties. Slightly higher in energy,
at around 3.6−3.8 eV, we find a 1ππ*-type state that is
localized on the A moiety (A 1ππ*). Both of these states
exhibit large oscillator strengths, and they are responsible for
the first photoabsorption band of the given compound in the
range of around 400−500 nm (which corresponds to photon
energies in the range of around 2.5−3.1 eV). In the triplet
manifold, the lowest state is a 3ππ*-type state that is localized
on the A moiety at an energy of roughly 2.4−2.5 eV. This state
is well-separated in energy from the higher triplet states, which
are found at energies of roughly 3.2 eV and higher. Based on
the above theoretical calculations, it is reasonable to envision
that the pool of NBI isomers has the potential to exhibit
distinguishing behavior in the TADF emission process.
2.3. Steady-State Photophysics. To experimentally
approach the eect of regioisomerism on the in-depth
photophysics of D−A−D compounds, UV−vis absorption
and steady-state photoluminescence (PL) spectra of diluted
Figure 3. Absorption and emission spectra (a−l) of synthesized isomers in dierent solvents.
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solutions of all of the compounds were measured. The
corresponding spectra are shown in Figure 3, while all
experimental details are combined in Table 1. An absorbance
peak at higher energy is due to the intense π−π*transitions.
Conclusively, the impact of the regioisomeric eect is even
more pronounced in the emission spectra of the solutions.
Notably, all investigated isomers show quite complicated PL
emissions, particularly visible in nonpolar solvents (toluene).
For the set of 53.X isomers, two broad and structureless
emission bands were observed. More precisely, the emission
bands exhibited by the isomers are as follows: the (i) 3,11
isomer�53.1: 512 nm (green) and 681 nm (red); (ii) 4,11
isomer�53.2: 485 nm (cyan) and 686 nm (red); (iii) 3,10
isomer�53.3: 497 nm (cyan) and 680 nm( red); and (iv)
4,10 isomer�53.4: 452 nm (blue) and 684 nm (red), which
clearly indicates that all four phenoxazine isomers of 53.X
could appear in a dual conformational form (D1eq−D2eq and
D1eq−D2ax). While switching solvent media to a more polar
one, the dominant emission occurred in the range 470−550
nm, strictly due to the two possible D1eq−D2ax conforma-
tions of the phenoxazine moiety. These experimental
results
36−38
are in good agreement with the TDDFT results
(vide supra) and represent confirmation of two conformers. In
the case of the 54.X sets, 54.4 also exhibited dual emission in
all solvents used, this time caused by the flexibility of the
dibenzoazepine unit that permits dierent conformations.
39,40
The dual CT emission can be ascribed to the mixture of nearly
planar or orthogonal conformers. These two dierent con-
formers exhibited two dierent emission peaks with a
heterogeneous ratio of intensity, showcasing the most
stabilized conformers among them. Considering the origin of
the peak at 420−525 nm, a very weak emission was found with
a weak CT character (which diers from the pure azepine
donor, ∼320−400 nm). Consequently, this is associated with a
less stable, nearly planar conformation, while the next one
(525−800 nm) with another CT state comes from the second
nearly orthogonal conformation of azepine. In contrast, 54.1
exhibited a very broad single CT emission in nonpolar solvents
(toluene), whereas in a polar solvent, the peak between 500
and 575 nm is probably due to a mixture of two dierent
conformers. The 55.X sets bearing DMAC as a donor part are
pseudoplanar segments and exhibit two possible conforma-
tions: a planar (1) and a crooked (2) form. Accordingly, the
first (1) arguably occurs at 500−840 nm in polar solvents
(DCM and THF) and at 550−800 nm in nonpolar solvents
(toluene), while the second (2) occurs at 425−580 and 450−
550 nm, respectively. Regarding 55.3 and 55.4 in polar
solvents, dual emissions clearly appeared in a nonhomoge-
neous order. In nonpolar solvents, very weak emission (E1)
from the crooked form appeared only in 55.3 and 55.1,
whereas in the case of 55.4, only E2emission due to the planar
conformation was observed (Figure 3).
This dierence in peak inhomogeneity indicates that 55.1
has a comparatively stronger ICT interaction between the
acceptor and donors.
41
In the 56.X series in a polar solvent, 56.4 and 56.3 exhibited
dual emission, most likely related to the formation of
aggregates. All these results indicate that the steady-state
photophysics of all the series are strongly aected by
regioisomerism as well as conformational isomerism from the
donor moieties. Once it is pronounced in a solution, it is worth
recognizing the nature of the interaction of regioisomers with
the host matrix in the solid state.
2.4. Time-Resolved Spectroscopic Analysis. To com-
prehend the detailed photophysics of the DF process of all the
isomers, we utilized time-resolved spectroscopic techniques,
and therefore, the obtained data are collected in Table 2. The
emissive properties of the entire set of dyes were analyzed in
the nonpolar, Zeonex, as well as in the polar 4,4′-bis(N-
carbazolyl)-1,1′-biphenyl (CBP), as the host matrices.
Interestingly, likewise in solvents, the significant impact of
the conformation of emitters was observed (as the presence of
both quasi-axial and quasi-equatorial conformations was
noticed), and depending on the host, we could identify some
similarities and discrepancies. In the solid matrix, this rotation
can be completely impeded by bulky donors and matrix
rigidity. On the contrary, in solvents, the entire population of
isomers exhibited dual emission from dierent conformers due
to the increased flexibility in this environment. To compare the
eect of regioisomers on DF properties, we considered
comparing whole sets of isomers as the performed measure-
ments revealed the impact on the photophysics to arise not
Table 1. Summary of Steady-State Photophysical Data of
Diluted Solutions of Compounds
a
compounds solvents λabs (nm) λPL (nm) ΦPL
b
53.1 TOL 323,391,509 512 and 681 0.4
DCM 324,390,496 519 <0.01
THF 323,359,468 523 <0.01
53.2 TOL 391,384,522 485 and 686 <0.01
DCM 324,389,522 496 <0.01
THF 322,385,510 497 <0.01
53.3 TOL 363,487 497 and 680 <0.01
DCM 356,472 507 <0.01
THF 358,469 508 <0.01
53.4 TOL 325,391,517 452 and 685 2.0
DCM 325,383,516 464 5.0
THF 322,383,500 518 <0.01
54.1 TOL 338,475 618 7.9
DCM 338,477 601 4.1
THF 338,469 637 2.0
54.4 TOL 335,455 600 6.7
DCM 335,462 580 1.5
THF 336,472 575 1.0
55.1 TOL 393,490 624 0.9
DCM 390,490 521 <0.01
THF 389,489 517 <0.01
55.3 TOL 390,482 621 0.9
DCM 389,481 501 <0.01
THF 385,480 608 <0.01
55.4 TOL 390 622 0.5
DCM 389 683 <0.01
THF 375 672 <0.01
56.2 TOL 327,385,454 552 6.3
DCM 326,381,451 613 0.5
THF 326,381,453 598 0.9
56.3 TOL 330,344,471 576 49.8
DCM 330,342,476 623 3.6
THF 330,343,464 611 12.9
56.4 TOL 328,340,460 580 45.3
DCM 326, 341,457 525 and 612 3.98
THF 327,341,449 524 and 613 7.5
a
Solution concentration: 10−5M; determined with an integrated
sphere in a normal atmosphere.
b
PLQY given in %.
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Table 2. Summary of the General Photophysical Properties Obtained from Time-Resolved Spectra
dye λem [nm]
a
host ΦPL
b
τPF [ns]
c
τDF [μs]
d
τRTP [ms]
e
DE/PF
f
kr107s−1
g
knr 108s−1
g
kISC 106s−1
h
kRISC 105s−1
h
Ea[eV]
i
S1[eV]
j
T1[eV]
j
ΔEST [eV]
k
53.1 664 Zeonex 4.5 13.63 ±1.15 25.16 ±2.96 1.81 1.17 7.01 4.73 0.11 0.0057 1.87 1.85 0.02
642 CBP 3.3 8.92 ±1.02 3.30 ±0.37 1.33 1.57 10.84 6.40 0.71 0.0221 1.93 2.32 −0.39
53.2 656 Zeonex 9.7 13.78 ±0.89 1.19 ±0.05 2.04 2.32 6.55 4.87 2.56 0.0305 1.89 1.89 0.001
634 CBP 12.4 12.5 ±0.47 15.719 ±3.2 2.36 2.96 7.01 5.62 0.21 0.0427 1.96 1.89 0.07
53.3 657 Zeonex 19.8 12.44 ±0.91 36.70 ±3.9 2.88 4.10 6.45 5.97 0.13 0.0239 1.89 1.84 0.05
641 CBP 4.9 6.74 ±0.13 2.76 ±0.1 1.49 2.97 14.11 8.75 0.88 0.0324 1.93 2.31 −0.38
53.4 632 Zeonex 17.6 14.27 ±0.90 4.85 ±0.596 3.63 2.66 5.77 5.50 0.96 0.0364 1.96 1.90 0.06
626 CBP 21.2 10.63 ±0.69 0.5 ±0.038 5.22 3.20 7.42 7.90 12.44 0.0415 1.98 1.91 0.07
54.1 617 Zeonex 41.5 7.79 ±0.33 53.27 7.51 2.01
617 CBP 12.0 6.17 ±0.27 18.21 ±1.29 0.02 19.12 14.26 0.33 2.01 2.05 −0.04
54.4 600 Zeonex 25.1 13.12 ±0.73 19.13 5.71 2.07
596 CBP 8.9 9.99 ±0.50 3.98 ±0.52 0.10 8.11 9.12 0.94 2.08 2.09 −0.01
55.1 598 Zeonex 25.7 16.44 ±0.60 8.9 ±0.836 2.06 5.11 4.52 4.10 0.34 0.0735 2.07 1.95 0.12
613 CBP 31.9 11.31 ±0.22 3.34 ±0.316 2.51 8.05 6.02 6.32 1.05 0.0495 2.02 2.42 −0.40
55.3 590 Zeonex 25.0 18.05 ±1.29 3147.88 ±55.25 0.86 7.42 4.16 2.57 0.001 0.0957 2.10 1.93 0.17
606 CBP 24.7 11.13 ±0.57 16.83 ±1.6 1.65 8.36 6.77 5.60 0.16 0.0325 2.05 2.25 −0.20
55.4 587 Zeonex 21.2 14.79 ±0.35 3.59 ±0.35 4.18 2.77 5.33 5.46 1.44 0.0994 2.11 1.94 0.17
604 CBP 39.1 10.43 ±0.21 14.94 ±0.73 4.43 6.90 5.84 7.82 0.36 0.0492 2.05 1.89 0.16
56.2 543 Zeonex 19.6 19.7 ±0.47 54.64 ±14.3 0.02 9.75 4.08 0.11 2.28 1.95 0.33
552 CBP 23.1 14.51 ±0.20 1.13 ±0.08 0.13 14.13 5.30 0.77 2.09 1.91 0.18
56.3 590 Zeonex 60.7 10.39 ±0.18 58.42 3.78 2.10 2.09 0.00
586 CBP 42.4 8.35 ±0.53 304.78 ±83.19 0.03 49.46 6.90 0.31 0.003 0.0014 2.11 2.18 −0.07
56.4 577 Zeonex 74.2 12.16 ±0.223 61.02 2.12 2.15 1.96 0.19
586 CBP 62.1 7.5766 ±0.06 81.96 5.00 2.12 2.29 −0.17
a
The maximum wavelength of PL spectra.
b
PLQY in the host under vacuum.
c
PF lifetime.
d
DF lifetime.
e
RTP lifetime.
f
Ratio of delayed emission (DF and RTP) to PF.
g
Estimates of krand knr assuming
that the emitting state is formed with unit eciency such that kr=Φ/τand knr =(1− Φ)/τ.
47
h
Values of RISC rate constant, kRISCkRISC = (DF/PF)/τDF.
47
Rough estimation of the rate constant values
as this system does not fulfill all the assumptions to use the above-mentioned equations.
47
i
Activation energy of triplet to singlet transfer (error ±0.01).
j
Singlet and triplet energy (error ±0.03 eV).
k
Energy splitting (error ±0.05 eV). All parameters are estimated at 300 K.
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only from the molecular structure itself but also from the host
materials. This phenomenon is well-evidenced for compounds
53.X in Zeonex (Figure 4a−h), for which the isomeric eect
barely influences the singlet 1CT state, whereas the triplet state
(both 3LE and 3CT) is significantly aected. This resulted in
very small energy ΔEST gaps, which are more than sucient to
trigger the TADF process via RISC transition. It must also be
underpinned due to the fact that dierent isomeric positions
lead to changes in electron density on asymmetric acceptors
and donors. This aects the 3LE and 3CT contributions in the
overall T1state. When it comes to 53.1 and 53.3, a greater
contribution from 3CT was observed, hinting at a potential
change in the dihedral angle formed by the donor merged at
position 3 of the NBI scaold in comparison to site 4.
Alternatively, this eect could be attributed to the mixture of
dierent conformers (Figure 4e−h, red spectra). The flexibility
of the polymer can be beneficial from the viewpoint of TADF
eciency as it can promote the formation of the more
favorable quasi-equatorial conformation, resulting in a very low
ΔEST due to the 1CT energy being close to the triplet energy of
the acceptor. Moreover, a significant observation was made
while isomers were deposited with the CBP matrix. Although
TADF-related emission was found, an unexpected shift of the
phosphorescence spectra to higher energies occurred (in
comparison to the Zeonex host). This process provided a
negative singlet−triplet gap (ΔEST) for isomers 53.1 and 53.3
Figure 4. Time-resolved PL decay profiles (intensity vs delay time) (a−d and i−l) and spectra (e−h and m−p) of compounds 53.1−53.4 in
Zeonex (a−h) and CBP (i−p). The energies correspond to the maximum emission peaks and λex = 355 nm.
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Figure 5. Time-resolved PL decay profiles (intensity vs delay time) (a−c and g−i) and spectra (d−f and j−i) of compounds 55.1−55.4 in Zeonex
(a−f) and CBP (g−l). The energies correspond to the maximum emission peaks and λex = 355 nm.
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in which the PXZ donor is substituted at position 3 (Figure
4m,o). For the remaining isomers of type, the dual
phosphorescence is observed for isomers 53.2, where the
donor is at position 4 (Figure 4n), while in this fashion, there is
no remarkable relationship between positions 10 and 11 of the
donor and photophysical outputs. Truly, the experimentally
determined inversion of the excited-state levels is not in line
with the results of the theoretical calculation, which revealed
that the lowest triplet excited-state energy should be the same
or lower than that of the singlet excited state. On the other
hand, the next triplet excited state is associated with the 3 or 4
position donor unit. We furthermore found the possibility of a
conformational change from quasi-equatorial to quasi-axial at
those positions. While it is tough to rationalize why the
emission from the triplet excited state at the acceptor moiety is
turned o, the observed phosphorescence emission from
isomers 53.1 and 53.3 originates from a triplet excited state
localized on the donor moiety at position 3. It is known that
such behavior is associated with the quasi-axial conformation,
where this particular donor unit is pushed over the acceptor
surface and locked. This specific molecular organization acts as
a steric hindrance and usually causes an increase of the energy
of the singlet excited state (1CT), which is also accompanied
by the RTP process.
42
Nevertheless, in our case, the impact is
completely dierent. While we still observe the TADF process,
this can be associated with a twisted ICT (TICT) eect,
commonly visible in multiresonance (MR) TADF emitters.
Here, the presence of a large steric hindrance and fully
decoupled HOMO−LUMO energy states do not allow for
normal CT.
43,44
We also notice a conformational impact in
isomer 53.2, where a mixture of two distinct conformers is
observed in the solid state (Figure 4n). Even though the entire
set of 53.X isomers disclosed moderate emission in the solid
state (ΦPup to 22%), an evident contrast in TADF properties
was observed among dierent regioisomers containing the
PXZ donor. First of all, isomers with the donor moiety at
position 4 have a higher TADF contribution (DF/PF) in
comparison to those in position 3 (2.36 for 53.2 and 1.33 for
53.1, respectively). Second, isomers with a donor group at
position 10 have higher TADF contribution than that of the
same group at position 11 (5.22 for 53.4 and 2.36 for 53.2,
respectively). This is associated with an increase of the
radiative rate constant on position 10, and kRISC, which is
important in order to increase the TADF contribution (Table
2). Interestingly, such distinctive dierences were also
determined in the remaining pool of IBZ, DMAc, and Cz
isomers. Accordingly, for IDB derivatives 54.X, unusual
behavior was found for the Zeonex host, in which we do not
observe delayed emission whatsoever, in contrast to the CBP
host, for which delayed emission is observed but at very long
times >5 ms (Figure S7). The unusual lack of this TADF or
RTP emission can be correlated with the singlet excited-state
energy that is similar to the localized triplet excited-state
energy of ca. 1.9−2.0 eV. This should be related to the visible
TADF emission. On the other hand, D−A derivatives based on
the IDB donor are well-known for their quasi-axial
conformation, which pushes emission to the RTP mecha-
nism.
45,46
Upon closer inspection of the behavior of isomers
54.1 and 54.4 in the CBP host, a small inversion was again
observed, which straightforwardly supports the concept of the
impact of quasi-axial conformation and TICT mechanisms. If
the presence of the quasi-equatorial conformation were the
case, the typical TADF mechanism would be observed. When
it comes to regioisomers with DMAC-based donors (55.X),
they exhibit a similar behavior as the above-mentioned 53.X
series. In a Zeonex matrix, although there is a higher ΔEST gap,
the TADF emission is still visible (Figure 5a−f). In a CBP
host, we observed ΔEST gap inversion for the same donor at
position 3 and a mixture of the phosphoresce emission for
position 4, which is again caused by the quasi-axial
conformation (Figure 5j−l). In a similar fashion to the isomers
from the 53.X series, the highest DF contribution was
Figure 6. Characteristics of the OLEDs based on emitters. Electroluminescence spectra (a,e). Current density-bias characteristics (b,f). EQE�
current density (c,g). EQE luminance characteristics (d,h).
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measured for derivatives with donors at positions 10 and 4
(55.4 DF/PF = 4.43), but in this case, not only position 10
contributed to the increase of kRISC but also position 4 (Table
2). In turn, a clear observation of DF emission with a thermally
activated process is made when the PH emission disappears
along with increasing temperature, and once again, emission
from the S1state becomes prominent. Regarding dyes 54.X
and 56.X in Zeonex, only 56.2 exhibited a delayed component
at room temperature, while the other isomers showed prompt
fluorescence (PF) exclusively. For 56.2 in Zeonex (Figure
S8d), a mixed contribution of minor TADF (500−600 nm)
and dominant RTP (600−850 nm) was observed due to higher
energy splitting compared to that of 53.X and 55.X. The
presence of PF alone in the 54.X set is attributed to the
nonemissive nature of T1at both low and high temperatures
(Figure S7a−f). While switching from a Zeonex to a CBP host,
we observed an intriguing behavior in dyes 53.1,53.3,55.1,
and 55.3, in which a negative ΔEST gap was noted (Table 2
and Figures 2m,o and 3j,k). An inversion of the ΔEST gap is
reasoned by emission from either a dierent triplet state
(above the T1state, often denoted as Tnwhere n> 1) or ES1 <
ET1. In this class of isomers, the presence of a higher triplet
energy (ET1) and lower singlet energy (ES1) results in a
substantial inversion of the ΔEST gap (>−0.20 eV).
2.5. Organic Light-Emitting Diode Analysis. A strong
correlation between distinct TADF emission behavior and the
substitution mode across the entire pool of regioisomers
prompted us to explore them as emitters in an OLED, thus
verifying their applicability as optoelectronic devices (Figure
6). Prior to device fabrication, the thermal stability of the
entire set of regioisomers was evaluated by means of
thermogravimetric analysis (TGA)/dierential scanning calo-
rimetry (DSC) techniques. In this context, we found most of
our dyes to be stable around 300 °C (for detailed results, see
Supporting Information, Figures S10−S21). To choose the
appropriate OLED structure, the HOMO and LUMO energy
levels of the compounds were determined by cyclic
voltammetry (CV) (Figure S3, Supporting Information). The
CV indicated very good electrochemical stability at both p and
n doping. The devices were fabricated using a thermal
evaporation technique.
For all compounds, the optimal configuration of the device
was obtained as follows: ITO/1,4,5,8,9,11-hexaazatriphenyle-
nehexacarbonitrile (HAT-CN) (10 nm)/N,N′(di(1-naphthyl)-
N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) (30 nm)/
10% of 5X.X in CBP (30 nm)/1,3,5-tri(m-pyridin-3-ylphenyl)-
benzene (TmPyPB) (40 nm)/lithium fluoride (LiF) (1 nm)/
Al (100 nm)] (Figure 5). The characteristics of the OLED
structures revealed a good eciency of 55.X TADF emitters in
a CBP host containing an OLED between 8 and 11% (Figure
6g,h), which exceeds the theoretical maximum of the OLED
based on only the fluorescence process (ca. 5%). The devices
based on isomers 53.X also exhibit electroluminescence based
on a TADF process; nevertheless, the low photoluminescence
quantum yield (PLQY) of the sole material itself explained the
lower device EQE (Figure 6c,d). OLEDs based on isomers
54.X and 56.X had emission mostly from the classical
fluorescence process. The highest luminance of the device at
around 28,000 cd/m2was observed for compound 55.4, which
also had the highest EQE (11.6%). From the “inverted”
emitters, the highest luminance and eciency were obtained
for isomer 55.1 with values of 22,000 cd/m2and 9.3%,
respectively. This suggests a rather low impact of the TICT
mechanism and conformation on the final eciency but rather
the overall emissivity of the compounds (PLQY). There was
no significant impact of the isomers on the overall stability and
roll-o of the devices; in this configuration, all of the devices
had good stability, which suggests the appropriate device
configuration.
3. CONCLUSIONS
In summary, a unique approach involving the use of higher-
order NBI-based regioisomers was employed to correlate the
impact of the host matrix on the conformational change of
emitters, leading to distinctive TADF emission mechanisms. A
better DF eciency (DF/PF ratio) was observed in isomers
where the donor is attached close to the carbonyl moiety of the
acceptor (4,10 isomers), i.e., PXZ and tBuCz, which exhibited
superior TADF photophysics compared to those of other
isomers. This phenomenon lets us clearly illustrate that the
photophysics of the compounds are influenced not only by
regioisomerism but also by the nature of the host material.
Moreover, the primary impact is observed in the T1state rather
than in the S1state, as transparently seen from the emission
profiles Analogously, S−T inversion was detected in the IDB-
linked dyes (3,11; 4,10) and tBuCbz-terminated species (3,10;
4,10) sets, although the energy inversion is not as pronounced
(<−0.20), unlike the previous dye sets. The best-performing
regioisomers (4,10) in the series, possessing electron-donating
DMAc groups, show a very high eciency of 11.6% with a
pronounced luminance of 28,000 cd/m2. The performed
studies delineate a new path for a better fundamental
understanding of the interaction of TADF emitters vs host
matrixes and its consequences, but it also can lead to the
revival of the NBI scaold, which postmodification can permit
access to highly ecient OLED emitters, which is now under
investigation in our group.
4. EXPERIMENTAL SECTION
4.1. Synthesis of Regioisomers. The synthetic procedures and
spectroscopic identification of the obtained regioisomers 53.1-4;
54.1,4;55.1,3-4; and 56.2-4 are given in Sections SI−8 of the
Supporting Information.
4.2. General Remarks. All of the reagents and solvents utilized in
the experiments were obtained commercially and used without further
purification. Reaction-grade solvents such as CH2Cl2, ethyl acetate,
and hexane were distilled before application. For reactions sensitive to
water, solvents underwent drying using the Swift solvent purification
system by MBraun. Meanwhile, reactions susceptible to moisture and
oxygen were conducted under an inert argon atmosphere. The
progression of each reaction was monitored using thin-layer
chromatography (TLC) on silica gel-coated (60 F254 Merck)
aluminum foil plates. Purification of intermediates and final products
was accomplished through column chromatography using a Merck
Kieselgel 60 Merck. Characterization of all intermediates and target
compounds was carried out using 1H NMR, 13C, and 2D NMR
spectroscopies and HRMS spectrometry (via EI-MS). NMR spectra
were recorded using Bruker AM 500 MHz, Bruker AM 600 MHz,
Varian 600 MHz, or Varian 400 MHz instruments, with
tetramethylsilane (TMS) employed as the internal standard. Chemical
shifts for 1H NMR are reported in parts per million (ppm) relative to
TMS (δ0.00 ppm) and CDCl3(δ7.26 ppm). Chemical shifts for 13C
NMR are expressed in ppm relative to CDCl3(δ77.16 ppm). Data
are presented in the following format: chemical shift, multiplicity (s =
singlet, d = doublet, dd = doublet of doublets, t = triplet, td = triplet
of doublets, q = quartet, p = quintet, hept = septet, and m =
multiplet), coupling constant (Hz), and integration. EI mass spectra
were recorded using an AutoSpec Premier spectrometer, while IR
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K
spectra were obtained using a JASCO FT/IR-6200 spectrometer.
TGA experiments were conducted using a Mettler-Toledo TGA/DSC
3+ thermal gravimetric analyzer under a nitrogen atmosphere with a
temperature range of 50 to 500 °C and a heating rate of 5 °C/min.
The temperatures corresponding to 5 and 10 wt % of mass loss were
determined. Additionally, DSC experiments (heating/cooling at 5
°C/min) were performed using a Mettler-Toledo DSC 3 analyzer.
4.3. Photophysics. Photophysical measurements were conducted
in a similar fashion as the preceding protocol.
34
The UV−vis spectra
were obtained by using a Shimadzu UV-2550 spectrophotometer,
while steady-state emission spectra were measured with a Jobin Yvon
Horiba Fluoromax 3 spectrofluorometer. PL spectra were calibrated
for the detector eciency based on specific calibration files provided
by the instrument manufacturer. PL measurements in solution were
conducted using PL cuvettes (Aireka Cells; path length: 1 cm).
Toluene solutions of the analyzed compounds were degassed through
5 freeze/thaw/pump cycles using a custom-made degassing cell
equipped with a young tap (path length: 1 cm). Temperature-
dependent experiments were performed within a Janis Research
cryostat cooled with liquid nitrogen. PLQYs were determined using
an integrating sphere both in solution and in the solid state. Matrix-
doped films were prepared on cleaned and dried sapphire disc
substrates, with 1 wt % of the emitter in the Zeonex host. PF,
phosphorescence, and DF spectra and decays were measured using
nanosecond-gated luminescence and lifetime investigations (ranging
from 400 ps to 1 s). A Q-Spark A50-TH-RE high-energy pulsed DPSS
laser (λem = 355 nm) and a Stanford Computer Optics sensitive gated
iCCD camera with subnanosecond resolution were utilized for these
experiments. Time-resolved analysis of PF/DF was conducted by
progressively increasing gate and integration times exponentially.
Temperature-dependent experiments under vacuum were carried out
within a Janis Research cryostat cooled with helium. Time-resolved
spectra were recorded using a Stanford Computer Optics 4Picos
iCCD camera, with gate and delay times exponentially increased to
avoid overlap. Each emission spectrum collected for the respective
emitter was integrated to generate an accurate luminescence decay
profile.
4.3.1. Devices. The OLEDs were fabricated following procedures
similar to those described previously.
26,34
HAT-CN was used as a hole
injection layer, NPB was used as a hole transport layer, and TmPyPB
was introduced as an electron transport layer. LiF and aluminum were
used as the cathodes. Organic semiconductors and aluminum were
deposited at a rate of 1 Å s−1, and the LiF layer was deposited at 0.1 Å
s−1. CBP was used as the host for all emitters. All materials were
purchased from Sigma-Aldrich or Lumtec and purified by temper-
ature-gradient sublimation in vacuum. OLEDs have been fabricated
on precleaned, patterned indium−tin-oxide (ITO)-coated glass
substrates with a sheet resistance of 20 Ω/sq and an ITO thickness
of 100 nm. All small molecules and cathode layers were thermally
evaporated in a Kurt J. Lesker Spectros evaporation system under a
pressure of 10−7mbar without breaking the vacuum. The sizes of
pixels were 4, 8, and 16 mm2. Each emitting layer has been formed by
the codeposition of the dopant and host at the specific rate to obtain
the 10% content of the emitter. The characteristics of the devices were
recorded using a 6 in. integrating sphere (Labsphere) inside the
glovebox connected to a source meter unit and an Ocean Optics
USB4000 spectrometer.
4.4. Calculations. DFT calculations were conducted by using the
QChem 5.0 software package. The ωB97X-D functional was
employed for geometry optimization, while ωPBE was appropriately
adjusted for calculations of excited-state levels. Nonequilibrium PCM
models were employed to account for solvation eects. Additional
information regarding the calculations can be found in the Supporting
Information (SI).
■ASSOCIATED CONTENT
*
sı Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acsami.3c19212.
1H, 13C, and 2D NMR spectroscopies along with high-
resolution mass spectrometry; detailed photophysical
methods and spectra; and computational data and
coordinates (PDF)
■AUTHOR INFORMATION
Corresponding Authors
Adam Kubas −Institute of Physical Chemistry, Polish
Academy of Sciences, 01-224 Warsaw, Poland; orcid.org/
0000-0002-5508-0533; Email: akubas@ichf.edu.pl
Przemysław Data −Department of Molecular Physics, Faculty
of Chemistry, ŁódźUniversity of Technology, 90-543 Łódź,
Poland; orcid.org/0000-0002-1831-971X;
Email: przemyslaw.data@p.lodz.pl
Marcin Lindner −Institute of Organic Chemistry, Polish
Academy of Sciences, 01-224 Warsaw, Poland; orcid.org/
0000-0002-5514-674X; Email: marcin.lindner@
icho.edu.pl
Authors
Prasannamani Govindharaj −Department of Molecular
Physics, Faculty of Chemistry, ŁódźUniversity of Technology,
90-543 Łódź, Poland
Aleksandra J. Wierzba −Institute of Organic Chemistry,
Polish Academy of Sciences, 01-224 Warsaw, Poland
Karolina Kęska −Institute of Organic Chemistry, Polish
Academy of Sciences, 01-224 Warsaw, Poland
Michał Andrzej Kochman −Institute of Physical Chemistry,
Polish Academy of Sciences, 01-224 Warsaw, Poland
Gabriela Wiosna-Sałyga −Department of Molecular Physics,
Faculty of Chemistry, ŁódźUniversity of Technology, 90-543
Łódź, Poland; orcid.org/0000-0002-4658-7922
Complete contact information is available at:
https://pubs.acs.org/10.1021/acsami.3c19212
Author Contributions
M.L. conceived and supervised the project as well as designed
the structure of emitters; A.J.W. and K.K. synthesized, isolated,
and characterized all emitters; P.G. carried out basic
photophysical, time-resolved spectroscopic, and electrochem-
ical studies then analyzed and interpreted all the results; P.D.
also analyzed and interpreted the spectroscopic and time-
resolved results and fabricated and analyzed the OLEDs;
G.W.S. analyzed the impact of the pure CBP matrix; M.A.K.
and A.K. performed the computational studies; M.L.
conceptualized the manuscript. P.G., A.J.W., P.D., A.K., and
M.L. contributed to writing the manuscript. The manuscript
was written through contributions of all authors. All authors
have given approval to the final version of the manuscript.
Notes
The authors declare the following competing financial
interest(s): The patent call dealing with synthesis of herein
discussed compounds constitutes a subject of the patent call
(P.444060) submitted to the Polish Patent Oce.
The data presented in this manuscript also constitute the
subject of the patent call, which was previously submitted to
the Polish Patent oce (P.444060).
■ACKNOWLEDGMENTS
A.J.W., K.K., and M.L. acknowledge support from the National
Centre for Research and Development, Poland, grant no.
LIDER/21/0077/L-11/19/NCBR/2020. M.L. is a recipient of
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L
a scholarship awarded by the Polish Ministry of Education and
Science to outstanding young scientists (2/DSP/2021). This
work has been published as part of an international cofinanced
project funded from the programme of the Minister of Science
and Higher Education entitled “PMW” in the years 2020−
2024; agreement no. 5005/H2020-MSCA-COFUND/2019/2.
M.A.K. acknowledges funding from the European Union’s
Horizon 2020 research and innovation programme under the
Marie Skłodowska-Curie grant agreement no. 847413. The
simulations reported in this study were carried out with the use
of the computational resources kindly provided to us by the
Wrocław Centre for Networking and Supercomputing (WCSS,
http://wcss.pl), the Centre of Informatics of the Tricity
Academic Supercomputer and Network (CI TASK, https://
task.gda.pl), and the PoznanSupercomputing and Networking
Center aliated to the Institute of Bioorganic Chemistry of the
Polish Academy of Sciences (PCSS, https://www.pcss.pl).
A.K. acknowledges support from the National Science Centre,
Poland, grant no. 2020/39/B/ST4/01952. We gratefully
acknowledge the generous support from these agencies.
G.W.S. and P.D. acknowledge support from the National
Centre for Research and Development, Poland, grant no.
POLBER/5/63/PrintedQDD/2022. P.D. and P.G. acknowl-
edge the Polish National Science Centre funding, grant no.
2022/45/B/ST5/03712.
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