Theoretical Study On The Effect Of Methylthio/Methylselenyl Substitution On The Charge Transport Properties Of Acenedithiophenes

Exploring the relationship between the molecular and electronic structure of small organic molecules and the charge transport properties of bulk materials has always been the focus of organic field-effect transistors（OFET）.Wherein,molecular stacking pattern in solid has a profound influence on the charge transport properties of organic semiconductors.Moreover,molecular stacking is controlled by complex weak intermolecular interaction.Therefore,regulating molecular stacking patterns by manipulating weak intermolecular interactions of organic semiconductor molecules to achieve the goal of improving charge transport properties in bulk materials still faces enormous challenges.Here we designed and predicted the molecules substituted byβ-methylselenyl on naphtho[1,2-b:5,6-b′]dithiopheneandanthra[2,3-b:6,7-b′]dithiophene（anti-β-MS-NDT,anti-β-MS-ADT）respectively,which together withβ-methylselenyl onbenzeno[1,2-b:4,5-b’]dithiophene（anti-β-MS-BDT）andβ-methylthio acenedithiophene derivatives（anti-β-MT-BDT,anti-β-MT-NDT,anti-β-MT-ADT）synthesized experimentally were systematically studied through multiscale theoretical calculation,including density functional theory（DFT）,Marcus charge transfer theory,Mont Caro simulation and the symmetry-adapted perturbation theory（SAPT）.The focus is put on the effect ofβ-methylthio andβ-methylselenyl group on intermolecular stacking of acenedithiophene derivatives in solid and charge transfer integrals.The results not only revealed the essential reasons whyβ-methylthio substitution converted molecular stacking from herringbone to pitchedπ-stacking,andβ-methylselenyl substitution transformed molecular stacking into 2D brickworkπ-stacking,but also found that the maximum carrier mobility of anti-β-MS-NDT and anti-β-MS-ADT crystal molecules could reach 3.30 cm²V^-1s^-1and 16.46 cm²V^-1s^-1,respectively.Hirshfeld surface analysis and SAPT were used to investigate the nonconjugated interaction of the molecules substituted byβ-methylthio andβ-methylselenyl substitutions.Wherein,the steric hindrance caused by the introduction of substituents promoted Csp₂-Csp₂···πinteraction to replace Csp₂-H···πto 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 replace conversion process,it is found that the energy of this intermediate state is larger than that of the actual ones.So the possibility of another dimer of molecules substituted byβ-methylthio exist in the form of face-to-face and molecules substituted byβ-methylselenyl exist in the form of end-to-face could be excluded.In addition,it is found that the molecules substituted byβ-methylselenyl exhibit phonon assistance that is conducive to charge transport during dynamic disorder,while the molecules substituted byβ-methylthio exhibit phonon scattering that is not conducive to charge transport during dynamic disorder.Through the study of intermolecular vibration modes that has a decisive effect on dynamic disorder,it showed that the molecules substituted byβ-methylselenyl had a weaker special intermolecular vibration mode than the molecules substituted byβ-methylthio,which would restrain the strong disordered vibration among molecules and reduce the amplitude of thermally induced vibration fluctuations,finally produce the higher charge transfer integrals.