Quantum Chemical Study on the Effect of Halogen Substitution on Photosensitization of Perylenequinonoid Photosensitizer

Taking hypomycin B（HMB）as the model compound，HF / 6-31G and TD-B3LYP / 6-31G methods have been employed to explore the effect of chlorine，bromine and iodine substitutions on molecular properties and photosensitization of perylenequinonoid photosensitizer（PQP）. It was found firstly that，the halogen substitutions lowered the EHOMO and ELUMO，and the ΔE. From chlorine，bromine to iodine substitutes，the EHOMO and ELUMO increased，while the corresponding ΔE decreased. Secondly，the halogen substitutions increased the molecular triplet-generating quantum yields and lowered the molecular lowest lying triplet energies，which resulted in the substitutes’similar 1O2 yields with their parent compounds. After halogen substitutions，the molecular adiabatic electron affinities increased，which made the substitutes possess lower O2· - -generating abilities than their parent compounds. Finally，the halogen substitutions lowered the intramolecular hydrogen bond energies，while enhancing the intramolecular proton transfer（IPT）barriers of cis isomers and lowering those of trans isomers on the ground state.