Juan Sancho Garcia

• PhD
• Professor at University of Alicante

Here, the key role played by theoretical calculations for molecules presenting an inverted singlet‐triplet excited state (e.g. S1 and T1) energy difference, or ΔEST < 0, whose interest has steadily raised in recent years fostered by experimental advances showing negative ΔEST values for a collection of real‐world systems is reviewed. The evolution...

We thoroughly assess here the recently developed PBE-DH-INVEST expression and its SOS1-PBE-DH-INVEST variant, both belonging to the family of Double-Hybrid (DH) density functionals, against the NAH159 dataset of organic molecules...

The discovery of triangular‐shaped molecules displaying an inverted singlet–triplet (INVEST) energy gap between their lowest singlet (S1) and triplet (T1) states opened the way for a new strategy to increase the internal quantum efficiency (IQE) of organic light‐emitting diodes (OLEDs), enhancing the reverse intersystem crossing (RISC) thanks to a...

Inverted singlet-triplet gap materials (INVEST) have emerged as an intriguing class of materials with potential applications as emitters in Organic Light Emitting Diodes (OLEDs). Indeed, this type of material exhibits a negative singlet-triplet energy gap (ΔEST), i.e., an inversion of the lowest singlet (S1) and triplet (T1) excited states, that go...

We theoretically study here the homolytic dissociation reactions of sterically crowded alkanes of increasing size, carrying three different (bulky) substituents such as tert‐butyl, adamantyl, and [1.1.1]propellanyl, employing a family of parameter‐free functionals ranging from semi‐local, to hybrid and double‐hybrid models. The study is complemente...

The theoretically disclosed, and experimentally confirmed, energy inversion of the lowest singlet (S1) and triplet (T1) excited states of organic molecules (i.e., Hund’s rule violation) is investigated herein with the aid of modern and nonempirically derived double-hybrid (DH) density functionals, in the search of the best trade-off between accurac...

The discovery of triangular-shaped organic molecules bearing an inverted singlet-triplet (INVEST) energy gap opened the way for a new strategy to increase the internal quantum efficiency of organic light-emitting diodes by enhancing the Reverse Intersystem Crossing (RISC) process thanks to a downhill process. However, all the molecular systems show...

El desarrollo y uso de la inteligencia artificial (IA) ha crecido exponencialmente en los últimos años, formando parte de numerosos campos relevantes y diversos, y por tanto irrumpiendo en la sociedad y en los comportamientos colectivos de su ciudadanía. Sin embargo, su importante papel no parece aún ser del todo apreciado por las personas, incluso...

The optical and mechanical properties of 2D semiconductors make them excellent candidates for the active components of plastic optoelectronic devices. Here, the integration of single‐layer WSe2 (1L‐WSe2) into a polystyrene (PS) film containing dispersed perylene orange (PDI‐O) molecules is investigated. The findings reveal a notable enhancement in...

In Chemistry, complexity is not necessarily associated to large systems, as illustrated by the textbook example of axial-equatorial equilibrium in mono-substituted cyclohexanes. The difficulty in modelling such a simple isomerization...

The effective calculation of static nonlinear optical properties requires a considerably high accuracy at a reasonable computational cost, to tackle challenging organic and inorganic systems acting as precursors and/or active layers of materials in (nano‐)devices. That trade‐off implies to obtain very accurate electronic energies in the presence of...

We develop and validate the SOS1-RSX-QIDH density functional, a one-parameter spin-opposite-scaled variant of the range-separated-exchange quadratic-integrand double-hybrid (RSX-QIDH) model. By entering into the family of spin-biased double hybrids, this new density functional benefits from an improved computational scaling that rivals with the one...

A computational design of linearly extended multiple resonance (MR)-type BN molecules based on DABNA-1 is proposed herein in the quest to find potential candidates that exhibit a negative singlet–triplet gap (ΔEST) and a large oscillator strength value. The impact of a proper account of the electron correlation in the lowest singlet and triplet exc...

We update the Quadratic Integrand Double-Hybrid (QIDH) model [J. Chem. Phys. 141, 031101 (2014)] by incorporating the nonempirical restored-regularized Strongly Constrained and Appropriately Normed (r2SCAN) meta-generalized gradient approximation exchange-correlation functional, thus devising a robust density functional approximation free of any em...

The accurate computation of static nonlinear optical properties (SNLOPs) in large polymers requires accounting for electronic correlation effects with a reasonable computational cost. The Random Phase Approximation (RPA) used in the adiabatic connection fluctuation theorem is known to be a reliable and cost-effective method to render electronic cor...

A computational design of linearly extended multiple resonance (MR)-type BN molecules based on DABNA-1 is proposed herein in the quest to find potential candidates that exhibit a negative singlet-triplet gap (ΔEST) and a large oscillator strength. The impact of a proper account of electron correlation in the lowest singlet and triplet excited state...

New heterocyclic diradicaloids based on boron and nitrogen‐doped polycyclic systems with open‐shell ground‐states are obtained via concomitant structural and quinoidal extensions, thus allowing to merge the best of both design strategies. A combination of experimental characterization and theoretical calculations have helped disclose their electron...

In this work, we focus on the understanding of the driving force behind the S1-T1 excited-state energy inversion (which would thus violate Hund's rule, making the S1 state lower in energy than the T1 state) of two non-benzenoid non-alternant hydrocarbons, composed of odd-membered rings. The molecules considered here have identical chemical composit...

New heterocyclic diradicaloids based on boron and nitrogen‐doped polycyclic systems with open‐shell ground‐states are obtained via concomitant structural and quinoidal extensions, thus allowing to merge the best of both design strategies. A combination of experimental characterization and theoretical calculations have helped disclose their electron...

The accurate computation of non-linear optical properties (NLOPs) in large polymers requires accounting for electronic correlation effects with a reasonable computational cost. The Random Phase Approximation (RPA) used in the adiabatic connection fluctuation theorem is known to be a reliable and cost-effective method to render electronic correlatio...

The importance of intermediate triplet states and the nature of excited states has gained interest in recent years for the thermally activated delayed fluorescence (TADF) mechanism. It is widely accepted that simple conversion between charge transfer (CT) triplet and singlet excited states is too crude, and a more complex route involving higher-lyi...

We theoretically study and characterize a set of rhombus-shaped nanographenes of increasing size, or n-rhombenes, where n = 2-6, displaying zigzag edges leading to an enhancement of the (poly)radicaloid nature and the appearance of intrinsic magnetism as a function of n. Due to that system-dependent radicaloid nature, we employ spin-flip methods ab...

Linear and cyclic acenes are polycyclic aromatic hydrocarbons that can be viewed as building blocks of graphene nanoribbons and carbon nanotubes, respectively. While short linear acenes demonstrated remarkable efficiency in several optoelectronic applications, the longer members are unstable and difficult to synthesize as their cyclic counterparts....

A family of non-empirical double-hybrid (DH) density functionals, such as Perdew–Burke–Ernzerhof (PBE)0-DH, PBE-QIDH, and their range-separated exchange (RSX) versions RSX-0DH and RSX-QIDH, all using Perdew-Burke-Ernzerhof(PBE) exchange and correlationfunctionals, is applied here to calculate the excitation energies for increasingly longer linear a...

The importance of intermediate triplet states and the nature of excited states has gained interest in recent years for the thermally activated delayed fluorescence (TADF) mechanism. It is widely accepted that simple conversion between charge transfer (CT) triplet and singlet excited states is too crude, and a more complex route involving higher-lyi...

The development of universal and accurate approximations for electronic structure calculations lies at the central core of (past and modern) research in theoretical and computational chemistry. For that purpose, any reliable method needs to treat in a balanced way exchange and correlation effects arising from the intrincate structure of matter at th...

El desarrollo progresivo y constante de nuevas tecnologías ha impactado en la sociedad de forma importante y, en ocasiones, de manera desapercibida. Se trata, sin duda, de un importante agente y motor para cualquier cambio social como constatamos al analizar su incidencia en aspectos tan variados como la productividad en la empresa e industria, o e...

The process by which pixels fluoresce in electronic displays uses energy highly inefficiently. The identification of fluorescent molecules with an unusual order of excited states opens up a fresh approach to tackling this issue. An unusual order of excited states for fluorescent molecules.

With the surge of interest in multiresonant thermally activated delayed fluorescent (MR-TADF) materials, it is important that there exist computational methods to accurately model their excited states. Here, building on our previous work, we demonstrate how the spin-component scaling second-order approximate coupled-cluster (SCS-CC2), a wavefunctio...

In this study, a set of 10 positional indolocarbazole (ICz) isomers substituted with dicyanomethylene groups connected via para or meta positions are computationally investigated with the aim of exploring the efficiency of structural isomerism and substitution position in controlling their optical and electronic properties. Unrestricted density fun...

The inversion of the lowest singlet and triplet excited state energy gap, in fully organic triangle-based compounds, can give rise to a new exergonic pathway to enhance the Organic Light Emitting Diodes (OLEDs) performance, going beyond the novel yet promising Thermally Activated Delayed Fluorescence (TADF) mechanism. If, on one hand, the origin of...

In this communication, we assess a panel of 18 double-hybrid (DH) density functionals for the modeling of the thermochemistry and kinetics properties of an extended dataset of 449 organic chemistry reactions belonging to the BH9 database. We show that most of DHs provide a statistically robust performance to model barrier height and reaction energi...

We calculate the relative energy between the cumulene and polyyne structures of a set of C4k+2 (k = 4-7) rings (C18, C22, C26, and C30 prompted by the recent synthesis of the cyclo[18]carbon (or simply C18) compounds. Reference results were obtained by a costly Quantum Monte-Carlo (QMC) approach, providing thus very accurate values allowing to syst...

We study the emergence of magnetism and its interplay with structural properties in a two-dimensional molecular crystal of cyclacenes, using density functional theory (DFT). Isolated cyclacenes with an even number of fused benzenes host two unpaired electrons in two topological protected zero modes, at the top and bottom carbon rings that form the...

Abstract: The lowest-energy singlet (S 1 ) and triplet (T 1 ) excited states of organic conjugated chro- mophores are known to be accurately calculated by modern wavefunction and Time-Dependent Density Functional Theory (TD-DFT) methods, with the accuracy of the latter heavily relying on the exchange-correlation functional employed. However, there...

The inversion of the lowest singlet and triplet excited state energy gap, in fully organic triangle-based compounds, can give rise to a new exergonic pathway to enhance the Organic Light...

The energy difference (ΔEST) between the lowest singlet (S1) and triplet (T1) excited state of a set of azaphenalene compounds, which is theoretically and experimentally known to violate Hund's rule giving rise to the inversion of the order of those states, is calculated here with a family of double-hybrid density functionals. That excited-state in...

The energy difference between singlet and triplet excitons, or ΔEST, is a key parameter for novel light-emission mechanisms (i.e., TADF or thermally activated delayed fluorescence) or other photoactivated processes. We have studied a set of conjugated molecules (peri-acenoacenes and their heteroatom-doped analogues) to observe the evolution of thei...

With the surge of interest in multi-resonant thermally activated delayed fluorescent (MR-TADF) materials it is important that there exist computational methods to accurately model their excited states. Here, building on our previous work, we demonstrate how the Spin-Component Scaling second-order approximate Coupled-Cluster (SCS-CC2), a wavefunctio...

With the surge of interest in multi-resonant thermally activated delayed fluorescent (MR-TADF) materials it is important that there exist computational methods to accurately model their excited states. Here, building on our previous work, we demonstrate how the Spin-Component Scaling second-order approximate Coupled-Cluster (SCS-CC2), a wavefunctio...

A collection of five challenging datasets, including noncovalent interactions, reaction barriers and electronic rearrangements of medium-sized hydrocarbons, has been selected to verify the robustness of double-hybrid functionals used in conjunction with the small DH-SVPD basis set, especially developed for noncovalent interactions. The analysis is...

We study the emergence of magnetism and its interplay with structural properties in a two dimensional molecular crystal of cyclacenes, using density functional theory (DFT). Isolated cyclacenes with an even number of fused benzenes host two unpaired electrons in two topological protected zero modes, at the top and bottom carbon rings that form the...

The search of compounds emitting in the near‐infrared (NIR) has been accelerated owing to their use in biomedical and telecommunications applications. In this regard, nanographenes (NGs) are attractive materials adequate for integration with other technologies, which have recently demonstrated amplified spontaneous emission (ASE) and lasing across...

Nanographenes with zigzag edges are predicted to manifest non-trivial π-magnetism resulting from the interplay of concurrent electronic effects, such as hybridization of localized frontier states and Coulomb repulsion between valence electrons. This provides a chemically tunable platform to explore quantum magnetism at the nanoscale and opens avenu...

The cover image is based on the Full Paper Assessing challenging intra‐ and inter‐molecular charge‐transfer excitations energies with double‐hybrid density functionals by Eric Bremond et al., https://doi.org/10.1002/jcc.26517

The so-called protobranching phenomenon, that is the greater stability of branched alkanes with respect to their linear isomers, represents an interesting challenge for approaches based on density functional theory (DFT), since it requires a balanced description of several electronic effects, including (intramolecular) dispersion forces. Here, we i...

We investigate the performance of a set of recently introduced range‐separated double‐hybrid functionals, namely ωB2‐PLYP, ωB2GP‐PLYP, RSX‐0DH, and RSX‐QIDH models for hard‐to‐calculate excitation energies. We compare with the parent (B2‐PLYP, B2GP‐PLYP, PBE0‐DH, and PBE‐QIDH) and other (DSD‐PBEP86) double‐hybrid models as well as with some of the...

This work describes the synthesis and properties of a dicyanomethylene‐substituted indolo[3,2‐b]carbazole diradical ICz‐CN. This quinoidal system dimerises almost completely to (ICz‐CN)2, which contains two long C(sp³)−C(sp³) σ‐bonds between the dicyanomethylene units. The minor open‐shell ICz‐CN component in the solid‐state mixture was identified...

We have investigated the origin of the S1‐T1 energy levels inversion for heptazine, and other N‐doped π‐conjugated hydrocarbons, leading thus to an unusually negative singlet‐triplet energy gap (ΔEST<0 ). Since this inversion might rely on substantial doubly‐excited configurations to the S1 and/or T1 wavefunctions, we have systematically applied mu...

The full harvesting of both singlet and triplet excitons can pave the way toward more efficient molecular light-emission mechanisms (i.e., TADF or thermally activated delayed fluorescence) beyond the spin statistics limit. This TADF mechanism benefits from low (but typically positive) singlet-triplet energy gaps or ΔEST. Recent research has suggest...

The synthesis of new carbon nanoforms with remarkable and fine‐tuned bulk properties still represents a formidable challenge, with cyclic organic nanorings emerging in recent years for the template‐driven design of this kind of systems. The design and engineering of these materials can be first controlled at the molecular scale, to further induce t...

We recently derived a new and simple route to the determination of the range-separation parameter in range-separated exchange hybrid and double-hybrid density functionals by imposing an additional constraint to the exchange-correlation energy to recover the total energy of the hydrogen atom [Brémond et al., J. Chem. Phys. 15, 201102 (2019)]. Here,...

DH‐SVPD is a tailored atomic basis set originally developed to enhance the domain of applicability of double‐hybrid density functionals to large molecular systems in weak interactions. In combination with any density functional belonging to this approximation, it provides an accurate estimate of noncovalent interaction energies at the cost of a dou...

We theoretically investigate here by means of DFT methods how the selective substitution in cyclic organic nanorings composed of pyrene units may promote semiconducting properties, analyzing the energy needed for a hole- or electron-transfer accommodation as a function of the substitution pattern and the system size (i.e. number of pyrene units). W...

Recent advances in the synthesis of stable organic (open-shell) polyrad-icaloids have opened their application as active compounds for emerg-ing technologies. These systems typically exhibit small energy differ-ences between states with different spin multiplicities, which are in-trinsically difficult to calculate by theoretical methods. We thus apply...

We investigate here the lowest‐energy (spin‐conserving) excitation energies for the set of He‐Ne atoms, with the family of nonempirical PBE, PBE0, PBE0‐1/3, PBE0‐DH, PBE‐CIDH, PBE‐QIDH, and PBE0‐2 functionals, after employing a wide variety of basis sets systematically approaching the basis set limit: def2‐nVP(D), cc‐pVnZ, aug‐cc‐pVnZ, and d‐aug‐cc...

Nanographenes with zigzag edges are predicted to manifest non-trivial pi-magnetism resulting from the interplay of hybridization of localized frontier states and Coulomb repulsion between valence electrons. This provides a chemically tunable platform to explore quantum magnetism at the nanoscale and opens avenues toward organic spintronics. The mag...

In this paper we describe the mechanism of light emission through thermally activated delayed fluorescence (TADF)—a process able to ideally achieve 100% quantum efficiencies upon fully harvesting the energy of triplet excitons, and thus minimizing the energy loss of common (i.e., fluorescence and phosphorescence) luminescence processes. If successf...

The recent synthesis of a C18 monocyclic ring constitutes a major breakthrough as a new all-carbon disclosed form. However, modern density functional theory approaches do not lead to the correct experimental polyynic structure and favor the cumulenic one instead. We demonstrate here that this serious drawback can be solved by recently developed ran...

We briefly present some of the most modern and outstanding non-conventional density-functional theory (DFT) methods, which have largely broadened the field of applications with respect to more traditional calculations. The results of these ongoing efforts reveal that a DFT-inspired solution always exists even for pathological cases. Among the set o...

The scalable production of homogeneous, uniform carbon nanomaterials represents a key synthetic challenge for contemporary organic synthesis as nearly all current fabrication methods provide heterogeneous mixtures of various carbonized products. For carbon nanotubes (CNTs) in particular, the inability to access structures with specific diameters or...

A computational protocol making use of Double Hybrid functionals in conjunction with a recently developed basis set tailored to reproduce non covalent interactions (hereafter named DH-SVPD) is here applied and tested for the evaluation of properties C60 fullerenes namely intermolecular interactions in the weakly bound C60 dimer and relative stabili...

A variety of planar π-conjugated hydrocarbons such as heptauthrene, Clar’s goblet and, recently synthesized, triangulene have two electrons occupying two degenerate molecular orbitals. The resulting spin of the interacting ground state is often correctly anticipated as S = 1, extending the application of Hund’s rules to these systems, but this is n...

While organic and inorganic semiconductors and metals films have been extensively studied, little attention has been devoted to the deposition of organic radicals on a substrate because these materials are considered not stable enough for evaporation. It was recently demonstrated that it is possible to evaporate and deposit organic radicals onto we...

A variety of planar {\pi}-conjugated hydrocarbons such as heptauthrene, Clar's goblet and, recently synthesized, triangulene have two electrons occupying two degenerate molecular orbitals. The resulting spin of the interacting ground state is often correctly anticipated as S = 1, extending the application of Hund's rules to these systems, but this...

In this communication, we present a new and simple route to derive range-separated exchange (RSX) hybrid and double hybrid density functionals in a nonempirical fashion. In line with our previous developments [Brémond et al., J. Chem. Theory Comput. 14, 4052 (2018)], we show that by imposing an additional physical constraint to the exchange-correla...

The scalable production of homogenous, uniform carbon nanomaterials represents a key synthetic challenge for contemporary organic synthesis as nearly all current fabrication methods provide heterogenous mixtures of various carbonized products. For carbon nanotubes (CNTs) in particular, the inability to access structures with specific diameters or c...

In this work, 1,3,5-tristyrylbenzene (1) and 1,3,5-tristyryl-s-triazine (2) derivatives decorated with carbazole moieties have been synthetized for the first time. Their photophysical properties and the nature of their low-lying electronic excited state were investigated combining steady-state and time-resolved fluorescence spectroscopy, along with...

Cyclic oligophenylenes possess remarkable electronic properties and are considered as viable templates for the hierarchical synthesis of well‐defined single‐walled carbon nanotubes. In article number 1801948, Andrés Pérez‐Guardiola, Ángel José Pérez‐Jiménez, Luca Muccioli, and Juan Carlos Sancho‐García demonstrate how these molecules can self‐assem...

We have recently demonstrated that carbazole-based biradicaloids are promising building blocks in dynamic covalent chemistry. To elucidate their intriguing dynamic covalent chemical properties, it is necessary to understand the physical origin of their biradical nature. To this end, here we focus on two quinoid carbazole systems substituted with di...

The nanoscale organization of cycloparaphenylene molecules when physisorbed on a graphite surface is theoretically investigated by means of atomistic molecular dynamics simulations employing a tailored and benchmarked force field. The landing of a single molecule is first considered, to progressively deposit more molecules to finally reach the full...

Unlike conventional thermally activated delayed fluorescence chromophores, boron-centered azatriangulene-like molecules combine a small excited-state singlet-triplet energy gap with high oscillator strengths and minor reorganization energies. Here, using highly correlated quantum-chemical calculations, we report this is driven by short-range reorga...

We systematically investigate the relationships between structural and electronic effects of finite size zigzag or armchair carbon nanotubes of various diameters and lengths, starting from a molecular template of varying shape and diameter, i.e. cyclic oligoacene or oligophenacene molecules, and disclosing how adding layers and/or end-caps (i.e. he...

The role of donor-acceptor (D-A) moieties on magnitudes such as reorganization energies and electronic couplings in CycloParaPhenylenes (CPP) carbon based nanohoops (i.e. conjugated organic molecules with cyclic topology) is highlighted via model computations and analysis of the available crystalline structure of N,N-dimethylaza[8]CPP. For the sake...

pre>We theoretically investigate, by means of atomistic molecular dynamics simulations employing a tailored and benchmarked force field, the nanoscale organization of cycloparaphenylene molecules when physisorbed on a graphite surface. The landing of a single molecule is first considered, to progressively deposit more molecules to finally reach the...

We systematically investigate the relationships between structural and electronic effects of finite size zigzag or armchair carbon nanotubes of various diameters and lengths, starting from a molecular template of varying shape and diameter, i.e. cyclic oligoacene or oligophenacene molecules, and disclosing how adding layers and/or end-caps (i.e. he...

Thermally Activated Delayed Fluorescence (TADF) offers the premise for all-organic light emitting diodes with quantum efficiencies competing those of transition metal-based phosphorescent devices. While computational efforts have so far largely focused on gas-phase calculations of singlet and triplet excitation energies, the design of TADF material...

A series of four novel deep blue to sky blue thermally activated delayed fluorescence (TADF) emitters (2CzdOXDMe, 2CzdOXD4MeOPh, 2CzdOXDPh and 2CzdOXD4CF3Ph) have been synthesized and characterized. These oxadiazole-based emitters demonstrated bluer emission compared with reference emitter 2CzPN thanks to the weaker acceptor strength of oxadiazole...

We apply a recently developed parameter-free double-hybrid density functional belonging to the quadratic-integrand double-hybrid model to calculate association energies (ΔE) and three-body effects (Δ³E) arising from intermolecular interactions in weakly bound supramolecular complexes (i.e., the dataset 3B-69). The model behaves very accurately for...

On the basis of our previous developments in the field of nonempirical double hybrids, we present here a new exchange-correlation functional based on a range-separated model for the exchange part and integrating a nonlocal perturbative correction to the electron correlation contribution. Named RSX-QIDH, the functional is free from any kind of empir...

We discuss the nature of electron-correlation effects in carbon nanorings and nanobelts by the analysis tool known as fractional occupation number weighted electron density (ρFOD) and the RAS-SF method, revealing for the first time significant differences in static correlation effects depending on how the rings (i.e. chemical units) are fused and/o...

We perform a theoretical study on a set of carbon nanorings (CycloParaPhenylenes or CPP) envisioned as molecular templates for the selective synthesis of carbon nanotubes. The shape of these precursors, originating from bending n phenylene units in para position until forming the corresponding nanoring [n]CPP, may drive the growth of armchair singl...

Understanding how molecular systems self-assemble to form well-organized superstructures governed by noncovalent interactions is essential in the field of supramolecular chemistry. In the nanoscience context, the self-assembly of different carbon-based nanoforms (fullerenes, carbon nanotubes and graphene) with, in general, electron-donor molecular...

Despite all the efforts, a complete mechanistic understanding of Thermally Activated Delayed Fluorescence (TADF) materials has not been fully uncovered yet. Part of the complexity arises from the apparent dichotomy between the need for close energy resonance and for a significant spin-orbit coupling between alike charge-transfer singlet and triplet...

We theoretically characterize a series of substituted cycloparaphenylene nanohoops to study the effect of incorporating an electron-withdrawing group into their cyclic structure. We systematically vary the nature, position, and number of nitrogen-containing acceptor groups in both neutral (pyridine) and charged forms (pyridinium and methylpyridiniu...