Substituent effect on electronic transition energy of dichlorobenzyl radicals

Highlights: We study the substituent effect on the electronic transition energy. We analyze the red-shifts of the origin bands of dichlorobenzyl radicals. We propose a model for delocalized Ͽ electronic structure. The model describes well the observed red-shifts of dichlorobenzyl radicals. Ring-substituted benzyl radicals exhibit electronic energies of the D₁ - D₀ transition being shifted to red region with respect to the benzyl radical. The red-shifts of disubstituted benzyl radicals are highly dependent on the substitution positions irrespective of substituents. By analyzing the red-shifts of dichlorobenzyl radicals observed, we found that the substituent effect on electronic transition energy is attributed to the molecular plane shape of delocalized Ͽ electrons. We will discuss the influences of locations of Cl substituents on the D₁ - D₀ transition energies of dichlorobenzyl radicals using Hückel's molecular orbital theory.