Torsional angle dependence and switching of inner sphere reorganisation energies for electron and hole charge transfer processes involving phenyl substituted diketopyrrolopyrroles; a density functional study

Determination of inner sphere reorganisation energies is important in the development of organic charge mediating materials and electron transfer reactions. In this study, hole and electron inner sphere reorganisation energies, lambda(h) and lambda(e) respectively, have been computed for the first time for a series of structurally related diketopyrrolopyrrole (DPP) molecular motifs. Inner sphere reorganisation energies for self-exchange electron transfer reactions are calculated as being lower than those associated hole transfer processes in model planar phenyl and thiophenyl substituted DPP systems. It is found that lambda(e) < lambda(h) for all planar ring/DPP core structures examined. The effect on lambda(h/e) of non-planarity between phenyl substituents and DPP core is explored in detail. The relative ordering of lambda(h) and lambda(e) is dependent upon the torsional angle of phenyl rings and reverses at twist angles of greater than 60 degrees such that lambda(e) > lambda(h).