Theoretical investigations on electronic and charge transport properties of novel organic semiconductors – Triisopropylsilylethynyl(TIPS)-functionalized anthradifuran and anthradithiophene derivatives

Triisopropylsilylethynyl(TIPS)-functionalized polyacenes, a new family of novel organic semiconductors, have attracted extensive interests due to their high solubility, good air stability, and high performance in organic field effect transistors (OFETs). In present study, the electronic and charge transport properties of a series of chalcogen-doped TIPS-pentacene (PENT) derivatives have been studied by density functional theory (DFT). Their electronic structures, ionization energies, electron affinities, reorganization energies, transfer integrals of possible hopping pathways, hole and electron mobilities, and anisotropic mobilities have be calculated to discuss the role of various factors affecting the charge transport properties of these novel organic semiconductors. Fluorination and chlorination effects on the electronic properties and reorganization energies of the studied molecules have also been studied. The calculated results show that the fluorination and chlorination are efficient strategies for tuning the molecular orbital level to decrease the charge injection barrier from metal electrode and improve their oxidative stabilities. Though the fluorination indeed lowers the lowest unoccupied molecular orbital (LUMO) levels of TIPS-PENT derivatives, it also leads to much larger reorganization energies and smaller electron transfer integrals. Thus, it may be not an effective way for TIPS-PENT derivatives to convert a p-type semiconductor to an n-type one. Our calculated hole mobilities for available experiment crystal structures are in good agreement with the experimental observation. The computed hole mobilities for TIPS-anthradithiophene (ADT) and TIPS-teracenothiophene (TT) are 0.622 and 1.186 cm2 V−1 s−1, respectively, which are in good agreement with the corresponding experimental values of 0.6 and 1.25 cm2 V−1 s−1, respectively. Their relative calculated electron mobilities are 0.607 and 0.637 cm2 V−1 s−1, respectively. The results show that they have high balanced hole and electron mobilities and may be promising candidates for ambipolar organic semiconductors. The studies on anisotropic mobilities of the selected derivatives show that they exhibit remarkable anisotropic behaviors and the hole and electron transfers along the parallel hopping pathway make the dominant contribution on their charge carrier mobilities.