Johannes Gierschner

• PhD
• Senior Research Prof. at Madrid Institute for Advanced Studies

A series of windmill‐shape heterocyclic molecules containing three N−B←N units, TBN and its derivatives, with quasi‐planar C3 symmetric backbone, are synthesized. The parent TBN exhibits a strongly allowed, doubly degenerate lowest excited state but suffers from very low fluorescence, due to very fast nonradiative decay rate through a conical inter...

A series of windmill‐shape heterocyclic molecules containing three N─B←N units, TBN and its derivatives, with quasi‐planar C3 symmetric backbone, are synthesized. The parent TBN exhibits a strongly allowed, doubly degenerate lowest excited state but suffers from very low fluorescence, due to very fast nonradiative decay rate through a conical inter...

Flexible optoelectronics is the need of the hour as the market moves toward wearable and conformable devices. Crystalline π‐conjugated materials offer high performance as active materials compared to their amorphous counterpart, but they are typically brittle. This poses a significant challenge that needs to be overcome to unfold their potential in...

The peripherical protons of the dye molecule hypericin can undergo structural interconversion (tautomerization) between different isomers separated by a low energy barrier with rates that depends sensitively on the interaction with local chemical environment defined by the nature of host material. We investigate the deuterium (D) isotope effect of...

Current research on organic light emitters which utilize multiple resonance‐induced thermally activated delayed fluorescence (MR‐TADF) materials is gaining significant interest because of the materials’ ability to efficiently generate color‐pure blue emission. However, the underlying reasons for high color purity remain unclear. It is shown here th...

The absorption and emission spectral shapes of a flexible organic probe, the distyrylbenzene (DSB) dye, are simulated accounting for the effect of different environments of increasing complexity, ranging from a homogeneous, low‐molecular‐ weight solvent, to a long‐chain alkane, and, eventually, a channel‐forming organic matrix. Each embedding is tr...

In developing an organic light-emitting diode (OLED) panel for a foldable smartphone (specifically, a color filter on encapsulation) aimed at reducing power consumption, the use of a new optically clear adhesive (OCA) that blocks UV light was crucial. However, the incorporation of a UV-blocking agent within the OCA presented a challenge, as it rest...

The complex photokinetics of donor-acceptor-donor triads with varying flexible spacer lengths (n = 4-10 carbon atoms) are investigated in liquid and solid solution, as well as in crystals, by steady-state and transient fluorescence spectroscopy combined with computational studies. For the short spacer (n = 4) in liquid solution, dynamic charge tran...

Perylene bisimide (PBI) dyes are known as red, maroon and black pigments, whose colors depend on the close π−π stacking arrangement. However, contrary to the luminescent monomers, deep-red and black PBI pigments are commonly non- or only weakly fluorescent due to (multiple) quenching pathways. Here, we introduce N-alkoxybenzyl substituted PBIs that...

Cyanoarene-based photocatalysts (PCs) have attracted significant interest owing to their superior catalytic performance for radical anion mediated photoredox catalysis. However, the factors affecting the formation and degradation of cyanoarene-based PC radical anion (PC•‒) are still insufficiently understood. Herein, we therefore investigate the fo...

Amplified Spontaneous Emission In article number 2206723, Juan Cabanillas‐González, Johannes Gierschner, Jinyi Lin and co‐workers report on how the spontaneous and stimulated emission properties of conjugated polymer blends are promoted through exciton transport disruption. The cover illustrates two alike polymer assemblies, the right one bearing t...

A highly efficient photocatalytic hydrogen evolution system was prepared by using an octupolar molecule as a building block of self‐assembled nanoparticles. The photocatalytic system showed an enhanced hydrogen evolution reaction (HER) rate upon the addition of halide ions, which was attributed to an external heavy atom effect enhancing intersystem...

Conjugated polymer blends coupled by Förster resonance energy transfer (FRET) have been widely exploited to achieve optically pumped lasers operating at very low pumping thresholds. Among the plaid of conjugated polymers and molecules exploited for optical gain, fluorene‐based polymers are considered front‐runners, based on their high photoluminesc...

Excited-state absorption (ESA) spectra of π-conjugated compounds are frequently calculated by (quadratic response) time-dependent density functional theory, (QR) TD-DFT, often giving a reasonable representation of the experimental results despite the (known) incomplete electronic description. To investigate whether this is inherent to the method, w...

Until now, surface-deposited stilbenes have been much less studied than other photochromic systems. Here, an asymmetrically substituted styrene incorporating a redox-active ferrocene moiety and a terminal alkyne group has been synthesised to investigate its photoisomerization in solution, and upon the formation of chemisorbed self-assembled monolay...

Since the pioneering discovery of a protein bound to poly(ethylene glycol), the utility of protein-polymer conjugates (PPCs) is rapidly expanding to currently emerging applications. Photoinduced energy/electron transfer reversible addition-fragmentation chain-transfer (PET-RAFT) polymerization is a very promising method to prepare structurally well...

Boric acid (BA) has been used as a transparent glass matrix for optical materials for over 100 years. However, recently, apparent room‐temperature phosphorescence (RTP) from BA (crystalline and powder states) was reported (Zheng et al., Angew. Chem. Int. Ed. 2021, 60, 9500) when irradiated at 280 nm under ambient conditions. We suspected that RTP f...

Boric acid (BA) has been used as a transparent glass matrix for optical materials for over 100 years. However, recently, apparent room temperature phosphorescence (RTP) from BA (crystalline and powder states) was reported (Zheng et al., Angew. Chem. Int. Ed.2021, 60, 9500) when irradiated at 280 nm under ambient conditions. We suspected that RTP fr...

State-of-the-art CASSCF/CASPT2 calculations are used to investigate the role of double excitations on the ground (GSA) and excited state absorption (ESA) spectra of distyrylbenzene (DSB), an important prototype medium-sized p-conjugated organic compound for optoelectronics. The multi-reference results are compared with linear and quadratic response...

Bent-shaped molecules incorporating terminal pyrene moieties were designed and synthesized aiming at promoting a variety of luminescent self-assembled materials. The novel compounds are fluorescent both in solution and in condensed...

Hypericin tautomerization that involves the migration of the labile protons is believed to be the primary photophysical process relevant to its light-activated antiviral activity. Despite the difficulty to isolate individual tautomers, it can be directly observed in single-molecule experiments. We show that the tautomerization of single hypericin m...

There has been much interest in dual‐emission materials in the past few years for materials and life science applications; however, a systematic overview of the underlying processes is so‐far missing. We resolve this issue herein by classifying dual‐emission (DE) phenomena as relying on one emitter with two emitting states (DE1), two independent em...

Hypericin has large potential in modern medicine and exhibits fascinating structural dynamics, such as multiple conformations and tautomerization. However, it is difficult to study individual conformers/tautomers, as they cannot be isolated due to the similarity of their chemical and physical properties. An approach to overcome this difficulty is t...

Luminescent small, all‐organic molecules are of tremendous interest in materials and life science applications. Nevertheless, targeted design requires a basic understanding of the excited state deactivation pathways of the molecules themselves, and the modulations of the processes that occur in the solid state. This particularly concerns crystallin...

Tautomerization is a fundamental chemical reaction which involves the relocation of a proton in the reactants. Studying the optical properties of tautomeric species is challenging because of ensemble averaging. Many molecules, such as porphines, porphycenes, or phenanthroperylene quinones, exhibit a reorientation of the transition dipole moment (TD...

Helical Molecular Orbitals—Hel‐MOs—have been tailored theoretically through the torsion angle of diphenylbutadiynes. Experimentally, suitable conformations have been locked by the synthesis of cyclic spirobifluorenes. In addition to present distinct Hel‐MOs, the developed systems are robust and feature remarkable, photophysical and chiroptical resp...

Research on solvent-free acrylic pressure-sensitive adhesives (PSAs) has tremendously grown over the last few decades due to the stringent regulations to control volatile organic compound emissions. They are mostly prepared in the presence of photoinitiators using high-energy UV light that causes several issues such as those associated with radiati...

Tautomerization is a fast chemical reaction where structures of the reactants differ only in the position of a proton and a double bond. Tautomerization often occurs in natural substances and is a fundamental process in organic- and biochemistry. However, studying the optical properties of tautomeric species is challenging due to ensemble averaging...

Several theoretical studies have proposed strategies to generate helical molecular orbitals (Hel‐MOs) in [n]cumulenes and oligoynes. While chiral even‐[n] cumulenes feature Hel‐MOs, odd‐[n] cumulenes may also present them if the terminal groups lie in different planes. However, the proposed systems have been either experimentally unfeasible or resu...

Solid-state luminescent materials that are sensitive to external stimuli are of enormous importance due to their potential for application as smart responsive materials and devices. Here we report the changes in the photophysical properties of a novel benzimidazole-based chromophore upon the formation of an inclusion complex with DMSO molecules in...

Charge-transfer (CT) crystals show unique transport and emission properties which are substantially different from those of individual electron donor (D) and acceptor (A) molecules constituting them. While the transport properties of CT crystals are well established as to enable the interpretation and prediction of their electrical properties, thei...

Dual emittierende (DE-)Verbindungen haben in den letzten Jahren viel Interesse in den Material- and Biowissenschaften gefunden; der vorliegende systematische, didaktische Aufsatz beabsichtigt eine eindeutige Darstellung des Phänomens, weist auf Fehlinterpretationen als auch auf weiterführende Literatur hin und mag so die weitere gezielte Entwicklun...

A combined spectroscopic and TD‐DFT case study was performed, to identify a robust method to calculate the complex near UV/Vis absorption spectra of various amino‐ vs. nitro‐substituted 2,4‐diphenylquinolines, which vary strongly under neutral and successively acidic conditions. For this, different DFT functionals were tested for geometry optimizat...

Several theoretical studies have proposed strategies to reach helical molecular orbitals (Hel-MOs) in [n]cumulenes. While chiral even-[n] cumulenes feature Hel-MOs, odd-[n] cumulenes may also present them if the terminal groups lie on different planes. However, the hitherto proposed systems have been either experimentally unfeasible or resulted in...

The present work explores a rational molecular design for a multicolor switchable mechanochromic molecular system with high fluorescence quantum yield. It is demonstrated that the reversible and high-contrast tricolor luminescence switching can be induced by combining the crystal-to-amorphous transition and unique crystal-to-crystal transition of a...

Self-assembled molecules for outstanding hydrogen evolution rate and durability should promise practical water splitting due to the versatile visible light absorption, low production cost and ease of control. Here, we adapted an amphiphilic molecule as a building block for efficient small molecule based self-assembled photocatalyst for hydrogen evo...

Two polymorphs with distinctly different fluorescence emission (green and yellow; G, Y) emanating from excitonic and excimeric contributions were prepared from solution as well as by using physical vapour transport. Based on crystal structure investigations, the vibrationally‐resolved excitonic emission is found to originate from a β‐Sheet arrangem...

Absorption spectra of Cyanine⁺Br⁻ salts show a remarkable solvent dependence in non-/polar solvents, exhibiting a narrow, sharp band shapes in dichloromethane but broad features in toluene; this change was attributed to ion pair association, breaking the symmetry of the cyanine, similar to the situation in the crystals (P.-A. Bouit et al, J. Am. Ch...

In the framework of optoelectronic luminescent materials, non-radiative decay mechanisms are relevant to interpret efficiency losses. These radiationless processes are herein studied theoretically for a series of stilbenoid derivatives, including distyrylbenzene (DSB) and cyano-substituted distyrylbenzene (DCS) molecules in vacuo. Given the difficu...

Polymorphs of organic semiconductors are of great interest as they shed light to structure‐property relationships. The full X‐ray thin film structure analysis of two polymorphs (B, G) of an important n‐type semiconducting dicyano‐distyrylbenzene based small molecule (CN‐TFPA) is reported. Drastically different structures of the monotropic phases ar...

A highly efficient organic photocatalyst (OPC) for photoinduced electron/energy-transfer reversible addition–fragmentation chain-transfer (PET-RAFT) polymerization was identified through a systematic catalyst design and discovery. The devised OPC offers excellent control over PET-RAFT polymerizations of methyl methacrylate at very low catalyst load...

Synthesis, processing, and characterization are reported for a series of tetracyanoplatinate Magnus’ salt (TCN-MS) derivatives—soluble derivatives of the generally intractable Magnus’ green salt—that feature the general structure [Pt(NH2R)4][Pt(CN)4] where R is a branched alkyl group or a ω-phenylalkyl group. In solutions, these coordination compou...

Determining the molecular orientation at the single molecule level is of key importance for a wide range of applica-tions ranging from molecular electronic devices to biomedical applications. In this work Surface-Enhanced Raman Scattering (SERS) was used to probe the light emitting conjugated polymer F8-PFB at the single molecule level using nanopa...

A data survey on experimental fluorescence quantum yields of (multi)substituted dicyano-distyrylbenzenes in fluid solution evidences that non-radiative decay increases with the Franck-Condon energy (EFC), being opposite to the conventional energy gap law. Quantum-chemistry indicates that this is controlled by access to the conical intersection (CI)...

The addition of chemical additives is considered as a promising approach for obtaining high-quality perovskite films under mild conditions, which is essential for both the efficiency and the stability of organic−inorganic hybrid perovskite solar cells (PeSCs). Although such additive engineering yields high-quality films, the inherent insulating pro...

Organocatalysed photoredox-mediated atom transfer radical polymerization (O-ATRP) is a very promising polymerization method as it eliminates concerns associated with transition-metal contamination of polymer products. However, reducing the amount of catalyst and expanding the monomer scope remain major challenges in O-ATRP. Herein, we report a syst...

Water soluble, highly fluorescent host-guest chromophore-cucurbit[8]uril supramolecular polymer (SP) bundles are investigated by polarized time-resolved photoluminescence spectroscopy, structural methods and quantum chemistry to fully reveal structural organization and heterogeneity, but in particular energy transfer dynamics, being of crucial impo...

A novel system of light-harvesting supramolecular block copolymers (SBCPs) in water is demonstrated. To realize cucurbit[8]uril (CB[8])-based SBCPs generating artificial light-harvesting in water, finely color-tuned supramolecular homopolymers (SHPs) comprising CB[8] host and different cyanostilbene guests (named as B, G, Y, and R) emitting blue, g...

In article 1705141, Johannes Gierschner, Soo Young Park, and co-workers report highly luminescent and efficient light-harvesting cyanostilbene/cucurbit[8]uril (CB[8])-based supramolecular block copolymer (SBCP) nanobundles in water. Mixing a pair of different-colored (blue, green, yellow, and red) supramolecular homopolymers through a dynamic cyano...

Solution-processable all-small-molecule organic solar cells (OSC) have shown a dramatic progress in improving stability and photovoltaic efficiency. However, knowledge of photoexcitation dynamics in this novel class of materials is very limited. To fully exploit the design capacities inherent in small molecule chemistry, the elementary processes an...

Highly sensitive optical detection of oxygen including dissolved oxygen (DO) is of great interest in various applications. We devised a novel room temperature phosphorescence (RTP) based oxygen detection platform by constructing core-shell nanoparticles with water-soluble polymethyloxazoline shells and oxygen-permeable polystyrene core crosslinked...

Highly sensitive optical detection of oxygen including dissolved oxygen (DO) is of great interest in various applications. We devised a novel room temperature phosphorescence (RTP) based oxygen detection platform by constructing core-shell nanoparticles with water-soluble polymethyloxazoline shells and oxygen-permeable polystyrene core crosslinked...

In this work, plasmonic nano-gaps consisting of a silver nanoparticle coupled to an extended silver film have been fully optimized for single molecule Surface-Enhanced Raman Scattering (SERS) spectroscopy. The SERS signal was found to be strongly dependent on the particle size and the molecule orientation with respect to the field inside the nano-g...

Solid state luminescence enhancement (SLE) of conjugated organic materials has found great impact in materials science, but a deep understanding is rather limited by now. Here, we investigate a prototype example of SLE materials, cyano-substituted distyrylbenzene (DCS) with varying systematically and subtly the substitution pattern (inter alia of t...

In this work we present friction-force microscopy (FFM) lattice-resolved images acquired on the (100) facet of the semiconductor organic oligomer (2Z,2′Z)−3,3′-(1,4-phenylene)bis(2-(4-butoxyphenyl)acrylonitrile) (β-DBDCS) crystal in water at room temperature. Stick-slip contrast, lateral contact stiffness, and friction forces are found to depend st...

A new set of four different fluorescent boron-rich hybrids based on an octasilsesquioxane core (T8) are presented herein. The syntheses have been carried out starting from styrene-containing ortho- and meta-carboranes and an adequately substituted octasilsesquixane derivative (p-BrStyrenylOS) via Heck coupling reaction. The carborane clusters are a...

The occurrence of polymorphs in crystals of luminescent π-conjugated organic materials is an intriguing matter, particularly because polymorphs can give rise to widely different broadband and amplified emission properties. Here, a new, highly luminescent polymorph of cyano-substituted distyrylbenzene, being a prominent example of “twist elasticity”...

A time-dependent density functional theory study is performed to reveal the excited state absorption (ESA) features of distyrylbenzene (DSB), a prototype π-conjugated organic oligomer. Starting with a didactic insight to ESA based on simple molecular orbital and configuration considerations, the performance of various density functional theory func...

The synthesis and spectroscopic characterization of the first set of tetra(p-dodecacarborane-stilbeno)ethylenes (TDSE), substituted either with a methyl or phenyl group in the 2-position (Ccluster) of the ortho-carborane, are described. The complex absorption properties are elucidated by TD-DFT calculations, stressing the importance of through bond...

In this work, a simple but effective molecular design strategy is developed for the generation of intense blue emission in the solid state including single crystals through the multiple secondary intermolecular interactions such as CF…HC hydrogen bonding. The synthesized novel imidazole-based excited-state intramolecular proton transfer (ESIPT) mol...

A new 2:1 donor (D):acceptor (A) mixed-stacked charge-transfer (CT) cocrystal comprising isometrically structured dicyanodistyrylbenzene-based D and A molecules is designed and synthesized. Uniform 2D-type morphology is manifested by the exquisite interplay of intermolecular interactions. In addition to its appealing structural features, unique opt...

Switchable luminescent organic materials with unusual high light-sensitivity in the bulk at room temperature are described. The compounds consist of two promesogenic photoactive cyanostilbene units linked by a flexible spacer with an odd number of carbon atoms, analogous to the structural design of a liquid crystal dimer. Experimental and computati...

Fluorination is frequently used to significantly change the properties of conjugated organic materials due to fluorine's exceptional properties; well known is the impact on the electronic structure, but also on the geometry despite fluorine's small size. Less known, the changes in the electronic and geometrical properties may provoke drastic change...

Supramolecular polymers (SPs) have received great attention because of their potential for various practical applications. As part of our search for SPs that are highly fluorescent in aqueous media, we designed a system based on a cucurbit[8]uril (CB[8]) host and a newly designed cyanostilbene guest. Fluorescence quantum yields of ≈0 % in the disas...

Resonant energy transfer (RET) is a key mechanism in organic optoelectronic devices, and its efficiency depends critically on the intermolecular arrangement of the active com-pounds. Supramolecular organization promoted by nanostructured supramolecular host-guest compounds (HGCs) is an elegant way of controlling the packing of the molecules inserte...

Supramolecular polymers (SPs) have received great attention because of their potential for various practical applications. As part of our search for SPs that are highly fluorescent in aqueous media, we designed a system based on a cucurbit[8]uril (CB[8]) host and a newly designed cyanostilbene guest. Fluorescence quantum yields of ≈0 % in the disas...

Absorption spectra of regio(ir)regular naphthalenediimide (NDI)- and perylenediimide (PDI)-bithiophene (2T) donor/acceptor (D/A) copolymers are surprisingly similar despite cross-conjugation in the regioirregular structures. This result is traced back to largely localized frontier molecular orbitals (FMOs) as revealed by (time-dependent) DFT calcul...

Naphthalenediimide-based random copoly-mers (PNDI-TVTx) with different π-conjugated dithienylvinylene (TVT) versus π-nonconjugated dithienylethane (TET) unit ratios (x = 100→0%) are investigated. PNDI-TVTx transistor electron/hole mobilities are affected differently, a result rationalized by molecular orbital topologies and energies, with hole mobi...

A set of triads in which o- and m-carborane clusters are bonded to two stilbene units through Ccluster−CH2 bonds was synthesized, and their structures were confirmed by X-ray diffraction. A study on the influence of the o- and m- isomers on the absorption and photoluminescence properties of the stilbene units in solution revealed no charge-transfer...

Empirical observation and quantum chemical explanation of a likely common but “overlooked” outcome of the donor–acceptor (D–A) approach to organic electronic materials are reported. The frontier molecular orbitals (FMOs) of D–A copolymers prepared from the amidated Pechmann dye unit (APD) are dictated primarily by this “acceptor,” largely because i...

The photophysics (spectral positions, band shapes, fluorescence quantum yields and lifetimes) of a series of fluorinated ladder type quaterphenyls L4P and L4P-Fn (n = 2, 4, 6) depend strongly on the degree and position of fluorine, despite the fact that substitution is not performed in the rings but only in methylene-bridges. This is driven by subt...

Intermolecular interactions are decisive in controlling optoelectronic properties of molecular materials. Polymorphism in one and the same material gives a unique opportunity to gain a direct insight into the intermolecular contributions. Here, stimulated emission properties in two polymorphs of a dicyanodistyrylbenzene derivative with multiple tri...

Natural anthocyanin pigments/dyes and phenolic copigments/co-dyes form noncovalent complexes, which stabilize and modulate (in particular blue, violet, and red) colors in flowers, berries, and food products derived from them (including wines, jams, purees, and syrups). This noncovalent association and their electronic and optical implications const...

Organic semiconductors (OSC) are attracting much interest for (opto)electronic applications, such as photovoltaics, LEDs, sensors or solid state lasers. In particular, crystals formed by small π-conjugated molecules have shown to be suitable for constructing OSC devices. However, the (opto)electronic properties are complex since they depend strongl...

Organic single crystal lasers have attracted much interest in materials science during the last years. On page 348, J. Gierschner and co-workers systematically explore the now available materials libraries to disentangle intra- and intermolecular contributions for the non-/occurrence, type, threshold, wavelength, and polarization of the light ampli...

This study describes the synthesis and characterization of a new zinc porphyrin-fluorescein dyad, the two chromophoric units being covalently linked by a 1,2,3-triazole bridge. The latter was formed by a Cu-catalyzed Huisgen 1,3-dipolar cycloaddition. The conformational analysis of this dyad (1) was performed by NOESY experiments, suggesting intera...

Metal-free organic phosphors can be an attractive smart optical sensing materials since, in such compounds, intersystem crossing (ISC) and the phosphorescence process are placed in subtle competition with fluorescence, internal conversion (IC), and non-radiative decay pathways. Here, we report a unique environment-dependent multi-luminescence switc...

Conjugated polymers with strongly twisted backbones, such as MEHPPV with fluorinated vinylene units (F-MEHPPV), demand a redefinition of the all-important 'effective conjugation length' ECL, which we extract here by a facile graphical method. In MEHPPV (being essentially planar), the ECL coincides with the 'maximum conducive chain length' MCC and e...

Metal-free organic phosphorescent materials are attractive alternatives to the predominantly used organometallic phosphors but are generally dimmer and are relatively rare, as, without heavy-metal atoms, spin-orbit coupling is less efficient and phosphorescence usually cannot compete with radiationless relaxation processes. Here we present a genera...

Supplementary Figures 1-7, Supplementary Tables 1-4, Supplementary Methods and Supplementary References

Materials design has become a vigorous aspect for organic solid-state lasing, which often lacks a fundamental understanding of structure–property relationships. The development of such an understanding is undertaken in this progress report, which systematically explores the now-available libraries of organic single crystals exhibiting light amplifi...

We report on a molecularly tailored 1:1 donor-acceptor (D-A) charge-transfer (CT) cocrystal that manifests strongly red-shifted CT luminescence characteristics, as well as noteworthy reconfigurable self-assembling behaviors. A loosely packed molecular organization is obtained as a consequence of the noncentrosymmetric chemical structure of molecule...