A theoretical study on physicochemical properties of elsinochrome A in ground state

Elsinochromes and hypocrellins are naturally occurring perylenequinonoid photosensitizers and have been given much attention in recent years. Elsinochromes contain a six-membered side ring, while hypocrellins have a seven-membered side ring. The rigidity of the six-membered ring leads elsinochromes to be less twisted than hypocrellins. To investigate the effect of the planarity of the aromatic system on the physicochemical properties of elsinochromes, we calculated structural, energetic and electronic properties of elsinochrome A by a combined ab initio method RHF/6-31G(d,p)//AM1 and compared the results with those of hypocrellin A and their active center, 4,9-dihydroxyl-3,10-perylenequinone. It was found that the skewedness of the perylene ring has slight effect on the physicochemical properties of perylenequinonoid photosensitizers, such as the isomerization barrier, the charge distribution, the dipole moment and the highest occupied molecular orbital energy level, which is helpful to understand the similar photosensitizing activities of EA and HA.