Theoretical study of charge-transport and optical properties of organic crystals: 4,5,9,10-pyrenedi-imides.

Abstract

This work presents a systematic study of the conducting and optical properties of a family of aromatic di-imides reported recently and discusses the influences of side-chain substitution on the reorganization energies, crystal packing, electronic couplings and charge injection barrier of 4,5,9,10-pyrenedi-imide (PyDI). Quantum-chemical calculations combined with the Marcus-Hush electron transfer theory revealed that the introduction of a side chain into 4,5,9,10-pyrenedi-imide increases intermolecular steric interactions and hinders close intermolecular π-π stacking, which results in weak electronic couplings and finally causes lower intrinsic hole and electron mobility in t-C5-PyDI (μh = 0.004 cm2 V-1 s-1 and μe = 0.00003 cm2 V-1 s-1) than in the C5-PyDI crystal (μh = 0.16 cm2 V-1 s-1 and μe = 0.08 cm2 V-1 s-1). Furthermore, electronic spectra of C5-PyDI were simulated and time-dependent density functional theory calculation results showed that the predicted fluorescence maximum of t-C5-PyDI, corresponding to an S 1→S 0 transition process, is located at 485 nm, which is close to the experimental value (480 nm).