Self-Consistent Quantum Mechanics/Embedded Charge Study on Aggregation-Enhanced Delayed Fluorescence of Cu(I) Complexes: Luminescence Mechanism and Molecular Design Strategy.

To elucidate the luminescence mechanism of highly efficient blue Cu(N^N)(POP)+-type thermally activated delayed fluorescence (TADF) materials, we have selected Cu(pytfmpz)(POP)+ (1) and Cu(pympz)(POP)+ (2) as targets to investigate the photophysical properties in both solution and solid phases. The self-consistent electrostatic potential (ESP) embedded charge within the quantum mechanics/molecular mechanics (QM/MM) method demonstrates a greater advantage over the charge equilibrium (QEQ) in accurately calculating atomic charges and reasonably describing the polarization effect, ultimately resulting in a favorable consistency between simulation and experimental measurements. After systematic and quantitative simulation, it has been found that complex 2, with an electron-donating group of -CH3, exhibits a much more blue-shifted spectrum and a significantly enhanced efficiency in comparison to complex 1 with -CF3. This is due to the widened HOMO-LUMO gap as well as the narrowed energy gap between the lowest singlet and triplet excited states (ΔEST), respectively. Then, the designed complex 3 is introduced with a stronger electron donor and larger tert-butyl group, which plays a key role in simultaneously suppressing the structural distortion and reducing the ΔEST. This leads to a faster reverse intersystem crossing process than that of the two experimental complexes in solution, turning out to be a new deep-blue-emitting material with excellent TADF performance.

Theoretical Studies and Design Strategies of Highly Efficient Two-Photon Excited Fluorescent Probes for Hydrogen Sulfide Detection through Simulation of Excited-State Dynamics.

Hydrogen sulfide (H2S) plays a critical role in numerous physiological and pathological processes, but an abnormal level of H2S in living systems can cause various diseases. To detect the level of endogenous H2S in a complicated biological system, the luminous mechanism of "turn-on" probe for H2S monitoring has been deeply explored through the simulation of excited-state dynamic processes, and the effect of different geometric modifications on optical properties has been minutely investigated based on molecular modeling. TD-DFT calculations demonstrate that line-type π-expanding in the molecular skeleton is beneficial for improving two-photon absorption (TPA) ability, but it can give rise to extremely large geometric relaxation, going against fluorescence emission. It is an effective way to suppress molecular skeleton scissoring vibration by introducing strong electron-withdrawing substituent groups (F, Cl, Br, CN) in benzopyran, and these compounds also have superior TPA properties in NIR. One of the potential materials in the application of biological imaging and H2S detection has been obtained, which simultaneously possesses easily distinguished spectra (with a Stokes shift as large as 77 nm), high luminous efficiency (with a quantum yield up to 20.07%), and large TPA cross section (952 GM at 950 nm).

Molecular Design of Highly Efficient Heavy-Atom-free NpImidazole Derivatives for Two-Photon Photodynamic Therapy and ClO- Detection.

Two-photon photodynamic therapy (TP-PDT), as a treatment technology with deep penetration and less damage, provides a broad prospect for cancer treatment. Nowadays, the development of TP-PDT suffers from the low two-photon absorption (TPA) intensity and short triplet state lifetime of photosensitizers (PSs) used in TP-PDT. Herein, we propose some novel modification strategies based on the thionated NpImidazole (the combination of naphthalimide and imidazole) derivatives to make efforts on those issues and obtain corresponding fluorescent probes for detecting ClO- and excellent PSs for TP-PDT. Density functional theory (DFT) and time-dependent DFT (TD-DFT) are used to help us characterize the photophysical properties and TP-PDT process of the newly designed compounds. Our results show that the introduction of different electron-donating groups at the position 4 of NpImidazole can effectively improve their TPA and emission properties. Specifically, 3s with a N,N-dimethylamino group has a large triplet state lifetime (τ = 699 µs) and TPA cross section value (δTPA = 314 GM), which can effectively achieve TP-PDT; additionally, 4s (with electron-donating group 2-oxa-6-azaspiro[3.3]heptane in NpImidazole) effectively realizes the dual-function of a PS for TP-PDT (τ = 25,122 µs, δTPA = 351 GM) and a fluorescent probe for detecting ClO- (Φf = 29% of the product 4o). Moreover, an important problem is clarified from a microscopic perspective, that is, why the transition property of 3s and 4s (1π-π*) from S1 to S0 is different from that of 1s and 2s (1n-π*). It is hoped that our work can provides valuable theoretical clues for the design and synthesis of heavy-atom-free NpImidazole-based PSs and fluorescent probes for the detection of hypochlorite.

Theoretical study of the tuning role of ß-methylthio or ß-methylselenyl on the charge-transport properties of acenedithiophenes derivatives.

To date, the manipulation of intermolecular nonconjugation interactions in organic crystals is still a great challenge due to the complexity of weak intermolecular interactions. Here we designed molecules substituted by ß-methylselenyl on naphtho[1,2-b:5,6-b']dithiophene and anthra[2,3-b:6,7-b']dithiophene, respectively (anti-ß-MS-NDT, anti-ß-MS-ADT), which together with anti-ß-MS-BDT synthesized experimentally all exhibited 2D brickwork π-stacking. Moreover, their maximum molecular carrier mobilities reached 3.30 and 16.46 cm2 V-1 s-1. These results indicated that the substitution of ß-methylselenyl could be a strategy to directionally adjust the parent herringbone stacking into 2D brickwork π-stacking. Hirshfeld surface analysis and symmetry-adapted perturbation theory (SAPT) were used to investigate the nonconjugated interactions in the pitched π-stacking formed by the ß-methylthio-substituted acenedithiophene derivatives and the 2D brickwork π-stacking of the ß-methylselenyl-substituted ones; wherein, the steric hindrance caused by the introduction of the substituents promoted Csp2-Csp2⋯π interactions to replace Csp2-H⋯π to stabilize the face-to-face stacking. Moreover, by calculating the decomposition energy of the intermediate state model of the molecular stacking mode that may exist in the replacement conversion process, it was found that the energy of this intermediate state was larger than that of the actual ones, finally confirming the inevitability of the actual existence in this stacking. In addition, because of the reduction in intensity of the special vibration modes, it could be found that the ß-methylselenyl substitution showed better phonon assistance than ß-methylthio substitution in terms of dynamic disorder. This study is a further step toward fully understanding the relationship between intermolecular interactions and regulation of the molecular stacking.

Theoretical Research and Photodynamic Simulation of Aggregation-Induced Thermally Activated Delayed Fluorescence Materials for Organic Light-Emitting Diodes.

The discovery and utilization of pure organic thermally activated delayed fluorescence (TADF) materials provide a major breakthrough in obtaining high-performance and low-cost organic light-emitting diodes (OLEDs). In spite of recent research progress in TADF emitters, highly efficient and stable TADF emitters in high-concentration solutions and in the solid state have been rarely reported, and most of them suffer from aggregation-induced quenching (ACQ). To resolve this issue, the aggregation-induced delayed fluorescence (AIDF) mechanism was studied in depth by the simulation of excited-state dynamic processes, and the effect of geometric modifications on optical properties was minutely investigated based on molecular modeling. TD-DFT calculations demonstrate that it is the key point for the transformation between prompt fluorescence and TADF to effectively regulate singlet-triplet energy difference and electron-vibration coupling by the aggregation effect. Then, excellent green and red TADF materials with very small singlet-triplet energy differences of 0.05 and 0.06 eV, high TADF quantum yields up to 57.53% and 39.19%, and suitable fluorescence lifetimes of 0.99 and 1.67 us, respectively, were designed and obtained, which demonstrate the potential application of these two TADF materials in OLEDs.

Theoretical Study on the Formation and Decomposition Mechanisms of Coelenterazine Dioxetanone.

Bioluminescence has been drawing broad attention due to its high signal-to-noise ratio and high bioluminescence quantum yields, which has been widely applied in the fields of biomedicine, bioanalysis, and so on. Among numerous bioluminescent substrates, coelenterazine is famous for its wide distribution. However, the oxygenation reaction mechanism of coelenterazine is far from being completely understood. In this paper, the formation and decomposition mechanisms of coelenterazine dioxetanone were investigated via density functional theory (DFT) and time-dependent (TD) DFT approaches. The results showed that the oxygenation reaction first occurred along the triplet-state potential energy surface (PES), after the intersystem crossing (ISC), second jumped to the diradical-state PES, and ultimately formed coelenterazine dioxetanone. For the decomposition mechanism of dioxetanone, the computational results showed that the chemiexcitation of neutral dioxetanone was more efficient than that of other dioxetanone species. Moreover, the diradical properties and the degree of ionic character are modified by the counter ions.

Theoretical insight on the charge transport properties: The formation of "head-to-tail" and "head-to-head" stacking of asymmetric aryl anthracene derivatives.

Organic semiconductors (OSCs) are widely used in flexible display, renewable energy, and biosensors, owing to their unique solid-state physical and optoelectronic properties. Among the abundant crystal library of OSCs, asymmetric aryl anthracene derivatives have irreplaceable advantages due to the interplay between their distinct π-conjugated geometry and molecular stacking as well as efficient light emission and charge transport properties that can be simultaneously utilized. However, the poor crystal stacking patterns of most asymmetric molecules limit their utility as excellent OSCs. Thus, it is crucial to clarify the structural features that enable the extremely ordered stacking and favorable electronic structure of asymmetric anthracene derivatives to become high-performance OSCs. This contribution investigates the charge transport properties of a series of asymmetric aryl anthracene derivatives to reveal the modulation factors of the molecular stacking modes and to explore the structural factors, which are beneficial to charge transport. The analysis demonstrated that the vinyl-linker facilitated the injection of hole carriers, and the alkynyl-linker effectively reduces the reorganization energy. Importantly, the linear polarizability and permanent dipole moment of a single molecule play a vital regulation to molecular stacking modes and the transfer integral of the dimer. The "head-to-head stacking" motif shows a compact stacking pattern and the maximum 2D anisotropic mobility more than 10 cm2 V-1 s-1. These findings sharpen our understanding of the charge transport properties in asymmetric organic semiconductors and are essential for developing a diverse range of high-performance OSC materials.

Photophysical Exploration of Alectinib and Rilpivirine: Insights from Theory and Experiment.

Due to the excellent characteristics of fluorescence-based imaging, such as non-invasive detection of biomarkers in vitro and in vivo with high sensitivity, good spatio-temporal resolution and fast response times, it has shown significant prospects in various applications. Compounds with both biological activities and fluorescent properties have the potential for integrated diagnosis and treatment application. Alectinib and Rilpivirine are two excellent drugs on sale that represent a clinically approved targeted therapy for ALK-rearranged NSCLC and have exhibited more favorable safety and tolerance profiles in Phase III clinical trials, ECHO and THRIVE, respectively. The optical properties of these two drugs, Alectinib and Rilpivirine, were deeply explored, firstly through the simulation of molecular structures, electrostatic potential, OPA/TPA and emission spectral properties and experiments on UV-vis spectra, fluorescence and cell imaging. It was found that Alectinib exhibited 7.8% of fluorescence quantum yield at the 450 nm excited wavelength, due to a larger electronic transition dipole moment (8.41 Debye), bigger charge transition quantity (0.682 e) and smaller reorganization energy (2821.6 cm-1). The stronger UV-vis spectra of Rilpivirine were due to a larger electron-hole overlap index (Sr: 0.733) and were also seen in CDD plots. Furthermore, Alectinib possessed obvious active two-photon absorption properties (δmaxTPA* ϕ = 201.75 GM), which have potential TPA imaging applications in bio-systems. Lastly, Alectinib and Rilpivirine displayed green fluorescence in HeLa cells, suggesting the potential ability for biological imaging. Investigation using theoretical and experimental methods is certainly encouraged, given the particular significance of developing integrated diagnosis and treatment.

Reliability of computed molecular structures.

When the structures of 1342 molecules are optimized by 30 methods and 7 basis sets, there appear 289 (21.54%) problematic molecules and 112 (8.35%) failed ones. When 278 problematic molecules are compared, the best methods are BHandH and LC-wPBE, while B97D, BP86, HFS, VSXC, and HCTH are very unreliable. When 179 problematic molecules are computed with larger basis sets, the smallest mean absolute deviation (MAD) of bond angle (2.3°) is shown by QCISD(T)/cc-pVTZ, while the smallest MAD of bond length (0.021 Å), the best SUM1 (4.9 unit), and the best SUM2 (2.4 unit) are shown by DSDPBEP86(Full), DSDPBEP86, PBE1PBE-D3, MP2, and MP2(Full) in combination with aug-cc-pVQZ, cc-pVQZ, Def2QZVP, Def2TZVPP, and/or 6-311++G(3df,3pd). Very large basis sets, for example, larger than cc-pVTZ usually have to be used to obtain very good structures and the performances of many density-functional theory methods are encouraging. The best results may be the limit of modern computational chemistry.

Photophysical Exploration of Zn(II) Polypyridine Photosensitizers in Two-Photon Photodynamic Therapy: Insights from Theory.

The high incidence and difficulties of treatment of cancer have always been a challenge for mankind. Two-photon photodynamic therapy (TP-PDT) as a less invasive technique provides a new perspective for tumor treatment due to its low-energy near-infrared excitation, high targeting, and minor damage. At present, the emerging metal complexes used as the photosensitizers (PSs) in TP-PDT have aroused great interest. However, most metal complexes as PSs in TP-PDT still face some problems, such as slow clearance, unsatisfactory two-photon absorption (TPA) characteristics, high price, low reactivity, and poor solubility. In this work, density functional theory and time-dependent density functional theory were used to characterize the one/two-photon response, solvation free energy, and lipophilicity of a series of novel PSs applied in TP-PDT. The results suggest that based on complex 1, replacing Ru(II) center with Zn(II) (complex 2) can effectively prolong the triplet excited state lifetime while reducing the cost and environmental pollution, and the azetidine heterospirocycles were introduced into the ligand scaffold (complex 3), which effectively reduced the vibration relaxation of the ligand group and improved the water solubility; further, the addition of acetylenyl groups subtly enhanced the light absorption and significantly improved the two-photon response (complex 4). In addition, all complexes met the requirement of a PS and could be used as potential candidates for TP-PDT. In particular, complex 4 has the advantages of high solvation free energy, a large TPA cross-section (1413 GM), a long triplet state lifetime (671 µs), good chemical reactivity, and low cost, and it is easy to be scavenged by organisms. Overall, this contribution may provide an important clue to formulate clear design principles for type I/II PSs and rational design of PSs with high intersystem crossing rates, a long lifetime, and therapeutic excitation wavelengths.

Theoretically seeking charge transport materials with inherent mobility higher than 2,6-diphenyl anthracene: three isomers of 2,6-dipyridyl anthracene.

2,6-Diphenyl anthracene (2,6-DPA) is a well-known anthracene derivative with high hole mobility (34 cm2 V-1 s-1) among p-type organic semiconductors (OSCs). In contrast, three 2,6-dipyridyl anthracene (2,6-DPyA) molecules (ortho-, meta-, and para-pyridyl), which are isoelectronic to 2,6-DPA showed relatively low mobility in experiments. To explore the origin of different charge transport properties and gain new inspiration on the design of novel organic semiconductor materials, the intrinsic hole transport property of 2,6-DPA and three isomeric 2,6-DPyAs were theoretically investigated and compared by quantum-chemical methodology and molecular dynamics simulation. The calculated results indicate that the intrinsic mobility of 2,6-DPyA-b (meta-) is superior to that of 2,6-DPA (12.73 vs. 3.54 cm2 V-1 s-1). Furthermore, the possibility that 2,6-DPyA-b may be strongly affected by thermal fluctuations is excluded because of the strong intermolecular C-H⋯N interactions (H-bonds). In addition, the crystal growth morphology prediction is considered in depth by the attachment energy (AE) model. The prediction results demonstrate that the strong intermolecular H-bonds in 2,6-DPyA do not facilitate the formation of a large and regular crystal face but rather the production of many grains and grain boundaries, which is not conducive to the charge carrier transport. This study reflects the paradox of the H-bond in OSCs and highlights the indispensability of the mesoscopic crystal growth morphology prediction in identifying high performance OSC materials and the establishment of the relationship between microcosmic organic molecules and macroscopic device performance.

Theoretical study and application of 2-phenyl-1,3,4-thiadiazole derivatives with optical and inhibitory activity against SHP1.

Src homology-2 domain-containing protein tyrosine phosphatase 1 (SHP1) is mainly restricted to hematopoietic and epithelial cells and widely accepted as a convergent node for oncogenic cell-signaling cascades. The development of efficient methods for rapidly tracing and inhibiting the SHP1 activity in complex biological systems is of considerable significance for advancing the integration of diagnosis and treatment of the related disease. With this aim, we designed and synthesized five 2-phenyl-1,3,4-thiadiazole derivatives (PT2, PT5, PT8, PT9 and PT10) here based on the reported SHP1 inhibitors (PT1, PT3, PT4, PT6 and PT7). The photophysical properties and inhibitory activities of these 2-phenyl-1,3,4-thiadiazole derivatives (PT1-PT10) against SHP1 were thoroughly studied from the theoretical simulation and experimental application aspects. The representative compound PT10 exhibited a larger quantum yield than the other molecules because of the smaller geometric relaxation and reorganization energy of the excited state, which was consistent with the results from the fluorescence experiments in organic solvents. In addition, PT10 showed a selective fluorescence response for SHP1 activity and low cytotoxicity in HeLa cells. Lastly, it indicated the potential application in two-photon cell fluorescence imaging in the future according to the calculated excellent two-photon absorption properties. In this contribution, firstly, we offered the fluorescent and activated molecule PT10 against SHP1, which achieved the integration of visualization and inhibitory activity of SHP1 preliminarily at the enzyme molecular level.

Persistent and Efficient Multimodal Imaging for Tyrosinase Based on Two-Photon Excited Fluorescent and Room-Temperature Phosphorescent Probes.

Tyrosinase is crucial to regulate the metabolism of phenol derivatives, playing an important role in the biosynthesis of melanin pigments, whereas an abnormal level of tyrosinase would lead to severe diseases. It is rather necessary to develop a sensitive and selective imaging tool to assess the level of tyrosinase in vivo. We thoroughly researched the luminous mechanism of the existing TPTYR probe and provided design strategies to improve its two-photon excited fluorescence properties. The designed probes benza2-TPTYR and product benza2-TPTYR-coumarin have large two-photon absorption cross sections at the NIR spectral region (41 GM/706 nm, 71 GM/852 nm), while benza2-TPTYR-coumarin possesses easily distinguishable spectrum in the visible region and a high fluorescence efficiency (ΦF = 0.27). What is more, novel two-photon excited multimodal imaging based on the pure organic small molecule benza1-TPTYR-coumarin (61 GM/936 nm) is proposed first, simultaneously possessing strong instantaneous fluorescent (563.79 nm) and persistent room-temperature phosphorescent emissions (767.68 nm, 0.54 ms).

Theoretical Study of a Two-Photon Fluorescent Probe Based on Nile Red Derivatives with Controllable Fluorescence Wavelength and Water Solubility.

Hypochloric acid (HOCl) plays a vital role in the natural defense system, but abnormal levels of it can cause cell damage, accelerated human aging, and various diseases. It is of great significance to develop new probes for detecting HOCl in biosystems nondestructively and noninvasively. The purpose of this work is to explore new chemical modification strategies of two-photon excitation fluorescence (TPEF) probes to improve the poor water solubility and low efficiency in imaging applications. Nil-OH-6 has a two-photon absorption cross-section value as high as 243 GM and attains a good quantum yield of 0.49. In addition, the modification of terminal groups with different azetidine-heterospirocycles or N,N-dialkyl fused amino groups to Nile Red can effectively improve the fluorescence efficiency as well as increase the solubility to some extent. This study provides some strategies to simultaneously improve the fluorescence performance and solubility of these two-photon probes and, hence, reliable guidance and a foundation for the subsequent synthesis of TPEF probes based on Nile Red.

Theoretical investigations on the charge transport properties of anthracene derivatives with aryl substituents at the 2,6-position-thermally stable "herringbone" stacking motifs.

High-performance organic semiconductor materials based on the small aromatic anthracene-core and its derivatives develop comparatively slowly due to the lack of a profound understanding of the influence of chemical modifications on their charge-transfer properties. Herein, the electronic properties and the charge transport characteristics of several typical anthracene-based derivatives with aryl groups substituted at the 2,6-site are systematically investigated by multi-scale simulation methods including Molecular Dynamics (MD) simulation and the full quantum nuclear tunneling model in the framework of density functional theory (DFT). To elucidate the origin of different charge transport properties of these anthracene-based materials, analysis of the molecular stacking and noncovalent intermolecular interaction caused by different substituents was carried out. The results indicate that the electron and hole injection capabilities and the air oxidation stability of the anthracene derivatives are greatly improved when the size of the aryl substituent increases. In addition, the incorporation of 2,6-site aryl substituents can inhibit the stretching vibration of the anthracene-core during charge transport, and allow molecular packing along the long axis (a-axis of DPA and BDBFAnt, and c-axis of dNaAnt) with almost no slippage, and the main transport channels remain unchanged, exhibiting more isotropic 2D transport properties. It should be emphasized that the edge-to-face dimers with smallest dihedral angles are closest to the thermally stable dimer model, with relatively larger π-orbital distributions in transmission channels (dimer 1, 2) and the largest spatial overlap, resulting in the largest hole transfer integral in DPA (Vh1/h2 = 57 meV). Although the analysis of the thermal disorder effect shows a phonon scattering effect, the maximum hole mobility of the DPA molecule is still as high as 1.5 cm2 V-1 s-1.

From luminescence quenching to high-efficiency phosphorescence: a theoretical study on the monomeric and dimeric forms of platinum(II) complexes with both 2-pyridylimidazol-2-ylidene and bipyrazolate chelates.

To develop solid-state light-emitting materials with high luminescence efficiency, determining the potential photophysics and luminescence mechanisms of the aggregation state remains a challenge and a priority. Here, we apply density functional theory to study the photophysical properties of a series of square planar Pt(ii) complexes in both monomeric and dimeric forms. We reveal that four monomeric Pt(ii) complexes are dominated by triplet ligand-to-ligand charge-transfer, and the lack of the triplet metal-to-ligand charge-transfer feature results in weak spin-orbit coupling (SOC), which leads to limited radiative rates; moreover, calculated nonradiative transition rates are one or two orders of magnitude higher than those radiative rates because a large amount of reorganization energy caused by the vibration of the bipyrazolate (bipz) ligand cannot be readily suppressed in the monomeric form. Therefore, four monomers exhibit photoluminescence quenching in CH2Cl2 solution in both theoretical calculations and experiments. However, in the solid state, the intense luminescence phenomenon indicates obviously distinct properties between the monomer and aggregation. We carried out a dimer model to interpret that the interaction of PtPt induces a metal-metal-to-ligand charge-transfer excimeric state, which leads more metal components to participate in the charge transfer and enhance the SOC effect. At the same time, the ligand vibration can be significantly reduced by the shortened distance, and there is a strong π-π packing interaction in the dimer; thus, an excellent quantum yield can be achieved in aggregation. In addition, we disclose that introducing bulky substituents bearing electron-donating groups at R' and R'' positions have little effect on the properties of the monomers; however, there is a benefit of restricting the internal reorganization energy through the intermolecular interaction when packing in the solid state. Therefore, substitutions can be tuned to improve the properties of monomers (such as emission energy and reorganization energy). We hope that our work will shine some light on Pt(ii) emitters in the fabrication of efficient OLEDs.

Molecular-Level Insight of Cu(I) Complexes with the 7,8-Bis(diphenylphosphino)-7,8-dicarba-nido-undecaborate Ligand as a Thermally Activated Delayed Fluorescence Emitter: Luminescent Mechanism and Design Strategy.

Investigation of the clear structure-property relationship and microscopic mechanism of thermally activated delayed fluorescence (TADF) emitters with high emission quantum yield is a direction worthy of continuous efforts. The instructive theoretical principle of TADF material design is critical and challenging. Here, we carried out theoretical calculation on two experimental Cu(I) complexes with the same 7,8-bis(diphenylphosphino)-7,8-dicarba-nido-undecaborate (dppnc) but different N^N ligands [dmbpy = 6,6'-dimethyl-2,2'-bipyridine (1) or dmp = 2,9-dimethyl-1,10-phenanthroline (2)] to briefly elaborate the structure-TADF performance relationship and luminescence mechanism. It was found that enhanced rigidity by the fused benzene ring between two pyridyl units in complex 2 leads to (i) higher allowedness of S1 → S0, (ii) more effective reverse intersystem crossing (RISC), and (iii) better relative stability of the T1 state, which could be responsible for its excellent TADF behavior. Thus, a strategy of extending π conjugation in the N^N ligand could be deduced to further enhance the quantum yield. We validated it and have succeeded in designing analogue complex 4 by extending π conjugation with an electron-withdrawing pyrazinyl. Benefiting from the smaller energy gap (ΔEST) and plunged reorganization energy between the S1 and T1 states, the rate of RISC in complex 4 (1.05 × 108 s-1) increased 2 orders of magnitude relative to that of 2 (5.80 × 106 s-1), showing more superiority of the TADF behavior through a better balance of RISC, fluorescence, and phosphorescence decay. Meanwhile, the thermally activated temperature of 4 is only 165 K, implying that there is a low-energy barrier. All of these indicate that the designed complex 4 may be a potential TADF candidate.

Crystal Engineering of Biphenylene-Containing Acenes for High-Mobility Organic Semiconductors.

Herein we report the synthesis, crystal structures, and semiconductor properties of new derivatives of bisnaphtho[2',3':3,4]cyclobut[1,2- b:1',2'- i]anthracene (BNCBA). It is found that the π-π stacking of BNCBA in single crystals can be largely modified by alkyl substituting groups of different lengths. In particular, the tetrahexyl derivative exhibits π-π stacking with an unusual zigzag arrangement. The variation of molecular packing also leads to a change in charge transport characteristics as found from the theoretical calculation of mobility on the basis of single-crystal structures. All of these BNCBA derivatives function as p-type semiconductors in solution-processed thin film transistors, and the tetrahexyl derivative exhibits a field effect mobility as high as 2.9 cm2/(V s).

Theoretical study on the charge transport properties of three series of dicyanomethylene quinoidal thiophene derivatives.

It is very important to analyse the most advantageous connection style for quinoidal thiophene derivatives, which are used in n-type organic semiconductor transport materials. In the present work, the charge transport properties of three series of quinoidal thiophene derivatives, oligothiophene (series A), thienothiophene (series B) and benzothiophene (series C), are systematically investigated by employing full quantum charge transfer theory combined with kinetic Monte-Carlo simulation. The single crystal structures of the molecules we had constructed were predicted using the USPEX program combined with density functional theory (DFT) and considering the dispersion corrected. Our theoretical results expounded how the different connection styles, including oligo-, thieno-, and benzo-thiophene in the quinoidal thiophenes derivatives, effectively tune their electronic structures, and revealed how their intermolecular interactions affect the molecular packing patterns and hence their charge transport properties by symmetry-adapted perturbation theory (SAPT). In the meantime we also elucidated the role of end-cyano groups in noncovalent interactions. Furthermore, it is clarified that quinoidal thiophene derivatives show excellent carrier transport properties due to their optimal molecular stacking motifs and larger electronic couplings besides their low energy gap. In addition, our theoretical results demonstrate that quinoidal oligothiophene derivatives (n = 3-5) with more thiophene rings will have ambipolar transport properties, so quinoidal thienothiophene and benzothiophene derivatives should be promising alternatives as n-type OSCs. When we focused only on the electronic transport properties in the three series of molecules, quinoidal benzothiophene derivatives were slightly better than quinoidal oligothiophene or thienothiophene derivatives.

Theoretical Investigations into the Electron and Ambipolar Transport Properties of Anthracene-Based Derivatives.

To obtain anthracene-based derivatives with electron transport behavior, two series of anthracene-based derivatives modified by trifluoromethyl groups (-CF3) and cyano groups (-CN) at the 9,10-positions of the anthracene core were studied. Their electronic structures and crystal packings were also analyzed and compared. The charge-carrier mobilities were evaluated by quantum nuclear tunneling theory based on the incoherent charge-hopping model. Our results suggest that introducing -CN groups at 9,10-positions of the anthracene core is more favorable than introducing -CF3 to maintain great planar rigidity of the anthracene skeleton, decreasing more lowest unoccupied molecular orbital energy levels (0.45-0.55 eV), reducing reorganization energies, and especially forming a tight packing motif. Eventually, the excellent electron transport materials could be obtained. The molecule 1-B in Series 1 containing -CF3 groups is an ambipolar organic semiconductor (OSC) material with a 2D transport network, and its value of µh-max/µe-max is 1.75/0.47 cm2 V-1 s-1 along different directions; 2-A and 2-C in Series 2 with -CN groups are excellent n-type OSC candidates with the maximum intrinsic mobilities of 3.74 and 2.69 cm2 V-1 s-1 along the π-π stacking direction, respectively. Besides, the Hirshfeld surface and quantum theory of atoms in molecules analyses were applied to reveal the relationship between noncovalent interactions and crystal stacking.