LAUSR

Abstract Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations based on B3LYP functional were carried out to understand the experimentally observed photophysical processes in the porphyrin-perylene bisimide ( HTPP - PDI ) dyad that exhibited long-lived triplet states. The results indicate that breaking the rigidity of PDI in HTPP - PDI is responsible to the generation of long-lived triplet states. Furthermore, six porphyrin derivatives were designed by introducing a 4,4′-dicarboxybutadienyl functional group to the porphyrin moiety and studied to investigate the substituent effects on the non-coplanarity, molecular orbital, and excitation wavelength of the porphyrin donor. This work showed that the functional group at β2-pyrrole- or meso-substitution tends to reduce the HOMO, LUMO, and the HOMO-LUMO gap of porphyrins. The results indicate that five of the six proposed porphyrin derivatives are promising donors in the HTPP-PDI dyad to replace HTPP for its potential use in photodynamic therapy.