The precise control of molecular packing patterns in solid-state materials is crucial for determining their charge transport properties. This study systematically investigates the molecular packing patterns and charge transport properties of triisopropylsilylacetylene (TIPS)-benzobenzene molecules functionalized with different molecular lengths using benzocyclobutadiene (BCBD) as a linker to connect polycyclic aromatic hydrocarbons. In the solid state, these molecules exhibited both herringbone stacking and 1D/2D π-stacking. We discovered an intrinsic relationship between the stacking motifs and the position of the TIPS in the investigated systems. Depending on the ratio (R) of skeleton lengths at both ends of the main chain with TIPS as the split point in the different ranges of ∼2.0, 2.0∼3.0, and 3.0∼, these crystals exhibited different packing patterns. Meanwhile, the R value is closely related to the anisotropy of mobility of these organic semiconductors. Multi-scale calculations, including density functional theory (DFT) and molecular dynamics (MD) simulations, were employed to examine the impact of incorporating the BCBD structural moiety on charge transport properties. The results demonstrate that BCBD effectively extends the LUMO orbitals and maintains a balance between hole and electron transport properties. This work aims to elucidate the experimental phenomena and establish a theoretical foundation for the development of high-mobility semiconductor materials.

Three anthracene derivatives with a 2,6-diphenylanthracene core and C-, O-, and S-bridged alkyl chain substituents (BEPAnt, BOPAnt, and BSPAn) exhibit relatively balanced high luminescence and mobility properties, and can be candidates for organic light-emitting transistor device materials. The optoelectronic properties including charge transport and fluorescent properties of three anthracene derivatives were investigated via quantum chemistry calculations. The results show that BEPAnt and BOPAnt exhibit high hole mobility (3.60 and 1.35 cm(2) V-1 s(-1)) and blue emission fluorescence quantum yield (>60%). In addition, the growth morphology of crystals/films can affect their properties, especially charge transport behavior but is often overlooked in theoretical evaluation. Hence, the morphological evolution of their organic thin-film is characterized by the attachment energy (AE) model. The predicted morphologies for BEPAnt and BOPAnt are consistent with the shape of their single-crystal films using the physical vapor transport (PVT) technique. The phenomenon of in-plane growth ratios for BEPAnt and BOPAnt crystal facets is reproduced well using the AE model. Notably, symmetrical hydrogen bond interactions within and between crystal layers facilitate the formation of a large flat film such as BOPAnt, which is conducive to better performance of charge transport properties in the experiment. We hope that this study can clearly provide details on the driving forces that affect the crystal surface growth rate, and then provide valuable guidance for the design and regulation of organic semiconductor molecules with ideal crystal morphology.

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 β-methylselenyl on naphtho[1,2-b:5,6-b']dithiophene and anthra[2,3-b:6,7-b']dithiophene, respectively (anti-β-MS-NDT, anti-β-MS-ADT), which together with anti-β-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 β-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 β-methylthio-substituted acenedithiophene derivatives and the 2D brickwork π-stacking of the β-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 β-methylselenyl substitution showed better phonon assistance than β-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.

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.

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.

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.

The impacts of intermolecular interactions on packing motifs and substitution positions on charge transport properties are elaborately delineated based on four crystal structures of dinaphtho-thieno-thiophene (DNTT) derivatives predicted by USPEX.

Molecular stacking motifs in solid play a pivotal role on the charge transport properties of materials. The relationship between molecular structure and packing motifs in solid remains challenging. In the present work, the single crystal structures of PEN-O, PEN-N, PEN-CF3 and TPDO were predicted by evolutionary algorithm using the USPEX program. The stacking motifs, the electronic structures and the stabilities of pentacene (PEN) derivatives are systematically investigated by employing density functional theory. Our study expounded how the introduction of heteroatoms (oxygen-atom and nitrogen-atom) and substituent (trifluoromethyl) adjust their electronic structure effectively to improve the capability of carrier injection. Hirshfeld surface analysis was performed for the intermolecular close contact points to rationalize the molecular stacking patterns in solid. In addition, electrostatic potential and energy decomposition by symmetry adapted perturbation theory are analyzed to reveal the effects of heteroatoms and substituents on charge distribution and noncovalent interactions. Through introducing heteroatoms and substituents into PEN, the charge redistribution leads to non-uniform electrostatic potentials of conjugated molecular skeleton, which results in the change of the stacking patterns from herringbone to π-stacking. Furthermore, incorporating oxygen-atom or nitrogen-atom into PEN decreases dispersion energies, while modifying PEN with trifluoromethyl increases the dispersion energy. However, both of them lead to the decrease of the electrostatic and exchange-repulsion energy.

Combining quantum-tunneling-effect-enabled hopping theory with kinetic Monte Carlo simulation and dynamic disorder effects, the charge transport properties of a series of N-hetero 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-PEN) derivatives with halogen substitutions were studied.

Hypochlorous acid (HOCL) plays a critical role in the natural defense system, but excessive production of HOCL leads to many diseases. It is very essential to monitor the distribution and level of endogenous HOCL. However, the applicable two-photon-excited fluorescent (TPEF) and phosphorescent probes for biological imaging and quantitative detection is rare due to low efficiency and vague mechanism. Therefore, we thoroughly researched the electron structures and luminous mechanisms of turn-on and ratiometric TPEF probe compounds and provide design strategies for high-efficient ratiometric TPEF probes. The designed ratiometric TPEF probe benzal-COCL and product benzal-CO have quite large two photon absorption (TPA) cross sections (143 GM/898 nm, 168 GM/988 nm), high fluorescence efficiencies (0.15, 0.28), and spectral resolution, contributing to the real-time monitoring level of HOCL in vivo. Besides, a long-lived two-photon-excited room-temperature phosphorescent probe benza2-COCL is provided first, which possesses a large TPA cross section (144 GM/838 nm) and time-resolved biological imaging (1.09 ms).

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.

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.

The charge transport properties of a series of rubrene derivatives were systematically investigated by density functional theory and molecular dynamics (MD) simulations. It was found that functionalizing electron-withdrawing groups (-CN, -CF3, or fluorination) on the peripheral phenyls not only enhance the chemical stability of materials but also favor electron injection by lowering the energy levels of frontier molecular orbitals and increasing the electron affinities. Derivatives 2-5 and 9, exhibiting packing motifs similar to rubrene but closer pi-stacking distances, possess large hole and electron-transfer integrals, significant bandwidths, and small effective masses, suggesting excellent ambipolar semiconductor behavior. The maximum hole(electron) mobilities in the Marcus hopping mechanism based on kinetic Monte Carlo simulation can reach 14.0-16.5(1.6-3.5) cm(2) V-1 s(-1). Interestingly, the antiparallel 2-D brick stacking and twisted backbones of fluorinated derivatives 11 and 12 result in nearly 1-D percolation network but balanced hole and electron transport property. In contrast, the parallel 2-D brick stacking of 14 leads to 2-D percolation network. Their maximum hole and electron mobilities fall in the range of 0.5-3.6 and 2.0-4.8 cm(2) V-1 s(-1). Furthermore, MD simulations show that dynamic disorder is strongly detrimental to the hole transfer but has a little influence on the electron transfer for 1-5. Moreover, severe twist of backbones of 9 leads to almost 1 order of magnitude lowered mobility. In addition, the influences of different substituents on the molecular structure, packing motif, and intermolecular reorganization energy are discussed.