Theoretical study of intramolecular proton transfer of perylenequinone

AM1 method is employed to calculate the barriers against intramolecular proton transfer (IPT) of perylenequinone (PQ). The results obtained are as follows: (i) Barriers against the IPT reaction of ground state, singlet excited state and triplet excited state of PQ are 89.75, 55.40 and 83.97 kJ/mol, respectively. (ii) Barriers against the IPT process of anion of PQ in ground state and singlet excited state are 80.12 and 79.91 kJ/mol, respectively. (iii) Barriers against the IPT of cation and anion radical of PQ (PQ ·+ and PQ ·- ) are 65.94 and 59.29 kJ/mol. (iv) The barrier against double proton transfer of PQ is 172.13 kJ/mol. (v) Two barriers against IPT of a type of perylenequinonoid photosensitizer (PQP), hypocrellin A (HA), are 89.24 and 88.07 kJ/mol. From these data conclusions can be drawn as follows: (i) IPT processes in ground state and excited state of PQ exist, but the transfer rate of excited state is much higher than that of ground state. (ii) It is almost impossible for PQ to transfer two protons simultaneously. (iii) IPT processes in anion, anion radical and cation radical of PQ still exist. (iv) The seven membered side ring of HA has no marked influence on its barrier against IPT.