The substituent effect on charge transport property of triisopropylsilylethynyl anthracene derivatives

Abstract

The charge transport property of two triisopropylsilylethynyl anthracene (TIPSAnt) derivatives TIPSAntBt and TIPSAntNa (bithiophene and naphthalene are introduced at the 2, 6-positions of the TIPSAnt core) were explored through quantum chemical method. To gain a better understanding of the substituent effect on the charge transport property, the results of the parent molecule TIPSAnt was also provided here for comparison. The substituent effect on the molecular geometry, reorganization energy, frontier orbitals, ionization potential (IP) and electronic affinity (EA), crystal property, transfer integrals and charge mobility, band structure and effective mass of the two compounds were investigated to establish the relationship between structures and properties. The introduced bulky TIPS groups made the two compounds adopt two-dimensional, face-to-face, π-stacking structures. The efficient overlaps of π-orbital and smaller π-stacking distance are proved to be the main reason for the high charge mobility of TIPSAntBt and TIPSAntNa. The hole mobilities of TIPSAntBt and TIPSAntNa are 0.88 and 3.60cm2V−1s−1, respectively, which is well consistent with experiment values (0.2 and 3.7cm2V−1s−1, respectively). For TIPSAntBt, the electron mobility (1.29cm2V−1s−1) is a little higher than that of hole due to the more effective transfer integrals of electron. On the contrary, the hole mobility of TIPSAntNa is 20 times larger than that of electron because of the smaller reorganization energy and larger transfer integral of hole, indicating that TIPSAntNa could be used as p-type semiconductor. For TIPSAntBt, the transfer integral is smaller than the reorganization energy, so the hopping mechanism plays a key role in the charge transport property. While the bandwidths and effective mass of TIPSAntNa agreed well with the calculated transfer integrals and charge mobility results. The introduced small substituents to TIPSAnt core contributed to the dramatically different charge transport property from an n-type semiconductor of TIPSAntBt to p-type semiconductor of TIPSAntNa, which shed light on molecular design for an n-type semiconductor through simple chemical structural modification.