Theoretical Investigations On Molecular Packing Motifs And Charge Transport Properties Of A Family Of Trialkylsilylethynyl Modified Pentacenes And Anthradithiophenes

Due to the light-weight,flexible,large-area,easy-processing and low-cost characteristics,organic semiconductor materials have been widely used into the fields of organic field-effect transistors,organic thin-film transistors,organic solar cells,organic light-emitting diodes and other organic optoelectronic devices.The macroscopic properties of these electronic devices are closely related to the microscopic charge transport properties of organic semiconductor materials.In general,high carrier mobility of organic semiconductor material is required for excellent performance of optoelectronic devices.So far,researchers have synthesized lots of organic semiconductor transport materials.Among these materials,pentacene is the most typical p-type transport material.However,the low stability and solubility,and the imperfect molecular packing motif limit its applications and developments.Trialkylsilylethynyl(TAS)functionalized materials would increase the solubility and might change the molecular packing motif into the desired 2-dimensional brick-like arrangement,which are beneficial for charge transport.In molecular crystals,the molecules combine together through intermolecular weak interactions.Owing to the complexities of intramolecular and intermolecular forces,crystal structure prediction is still difficult and time-consuming.In addition,different intermolecular interactions lead to different molecular packing motifs.The charge transport properties of organic semiconductors depend highly on the relative positions of the nearest-neighboring dimers.Therefore,it is important to construct the relationships between electronic structure,molecular packing motif and material properties in theory in order to explain the experimental phenomena and provide the design ideas and theoretical support for experiment.We choose six representative TAS-modified molecules,TAS-pentacene(TAS-PEN)and TAS-anthradithiophene(TAS-ADT),to detailedly study the effects of different TAS-substitutions and different backbones on the intermolecular interactions,crystal packing motifs and charge transport properties.Hirshfeld surface analyses and SAPT energy decomposition analysis were carried out to study the intermolecular interactions.Quantum nuclear enable hopping model combined with molecular dynamics simulations were performed to investigate the charge transport properties.The results show that all these molecules are more suitable for hole transport.Furthermore,molecules with ADT skeleton and smaller TAS groups possess larger hole reorganization energies.A regular phenomenon exists that the smaller the TAS group is,the shorter the long-axis displacement and the longer the short-axis displacement are between the nearest-neighboring ?-stacking dimers.It can be explained by the balance relationship between repulsion interaction and attractive dispersion interaction.Furthermore,thiophene-substitution would introduce additional electrostatic interactions and lots of weak C-H?S hydrogen bonds.These additional electrostatic interaction introduced by S-atoms accounts for the very different molecular packing motifs between TAS-PENs and TAS-ADTs.The calculated disorder-free hole mobilities indicate that TAS-ADTs possess better intrinsic hole transport properties.The thermal disorder plays significant role on the transfer integral fluctuations for TAS-PENs,while for TAS-ADTs systems,the thermal disorder has relatively smaller effect on the transfer integral fluctuation and thus the hole mobilities.Furthermore,the syn-TAS-ADTs show more serious non-local electron-phonon interactions than the anti-TAS-ADTs.We speculate that the substantially additional C-H?S weak hydrogen bonds in TAS-ADTs stabilize the molecules in crystal environments and result in the slighter transfer integral fluctuations,and the larger S?S overlap in the syn-TAS-ADTs between neighboring molecules accounts for the more serious non-local electron-phonon interactions.