Hopping Transport in Conductive Heterocyclic Oligomers:  Reorganization Energies and Substituent Effects

Molecular scale charge motion in disordered organic materials at ambient temperature occurs via a hopping-type mechanism with rates dictated both by the charge transfer integral and by the reorganization energy due to geometric relaxation. This contribution presents a systematic theoretical analysis of cation internal reorganization energies for a broad family of organic oligoheterocyclesvariation of reorganization energy with oligomer chain length, heteroatom identity, and a range of heterocycle substituents provides key information on important structural properties governing internal reorganization energies. At room temperature, the range in reorganization energies induced by substituent variations corresponds to a >102-fold variation in intrinsic hole transfer rate, suggesting that changes in reorganization energy dominate variations in charge-transfer rates for many semiconducting/conducting oligomers.