Is charge-transfer excitation through a polyalkane single-bond chain an intramolecular charge-transfer?: EOM-CCSD and LC-BOP study

Abstract

We performed intra- and intermolecular charge-transfer (CT) excitation calculations of (a) H2N–(CH2–CH2)n–NO2 and (b) its equidistant H2N-H……H-NO2 using EOM-CCSD (n = 1 ∼ 5) and time-dependent long-range corrected density functional theory (n = 1 ∼ 10). The calculation results show that polyalkane [polyethylene oligomer] chain has almost no effect on CT excitation energy between donor and acceptor. That is, CT excitation energy through the polyalkane chain behaves closely to intermolecular CT excitation. Decomposition of the optical excitation energies of (a) and (b) into HOMO-LUMO gap and excitonic binding energy revealed that alkane chain does not affect HOMO-LUMO gaps, while conjugated polyene [polyethylene oligomer] chain medium reduces HOMO-LUMO gaps by delocalization.