| The quality of photosensitizer is a key factor for the efficiency of photodynamic therapy (PDT). In recent years, much research attention has been focused on a novel type of photosensitizer, perylenequinonoid derivatives (PQD). Experimental evidences have suggested that PQD have the potential to replace Photofrin II as the latest photodynamic medicine.PQD are complex molecules with large conjugated system. There are many hydrogen atoms that are liable to transfer in their molecules; moreover, these hydrogen atoms transfer with extremely high speed. So it is an arduous task to analyze their experimental results. So far, the essence of the intramolecular hydrogen transfer (IHT) reaction of PQD has not been confirmed according to the experiments. Also the origin of the different IHT modes of HA and HYP remains unclear.Petrich and co-workers have estimated that excited-state intramolecular hydrogen transfer (ESIHT) present in PQD is critical for them to reserve their photosensitive activity. Different types of experimental techniques have been applied in order to illuminate this hypothesis, however, it is difficult to reveal the intrinsical relationship between the ESIHT process and the photosensitive activity of PQD by experiments.The molecular structures of PQD have also been modified in order to enhance their photosensitization. But there are no rules that may guide these modifications. They only depend on experience and experimental tests.In this thesis, the B3LYP/6-31G method has been applied to the IHT reaction of perylenequinonoid photosensitizer hypocrellin A (HA) and its model compounds. In order to ascertain the essence of its IHT reaction, the results have been analyzed with the linear fitting method.To elucidate the intrinsical relationship between the ESIHT reaction and the photosensitive activity of PQD, the coarse potential energy surface (PES) of PQ (the active center of HA) is constructed by the CIS/6-31G method. In the meantime, the potential energy profiles for the ESIHT reaction of PQ and some similar modelcompounds are constructed with the minimum energy path (MEP) method.We also applied naphthazarin as a model molecule of PQD to illuminate the effect of different types of side chains.To clarify the origin of difference between HA and HYP, we employed the density functional and CIS method to the ground state and excited state of eight isomers of HA respectively. The vertical excitation energies of these isomers have been calculated with the TD-B3LYP/6-31G* //CIS/6-31G method.The most notable points in this thesis are as follows:1. HA executes a quick IHT reaction in the ground state at room temperature. There is little difference between IHT barrier and charge distribution of HA and the model compounds, which indicates that side chain has little effect on IHT reaction of HA. As for HA series compounds, IHT barrier is linear to the change of H-bond length or O-H bond length. There is a charge separation process coupled with the IHT reaction. The Coulombic interaction dominates the IHT process, which indicates that the IHT reaction of HA is a proton transfer process in nature.2. A schematic excited-state PES of PQ is obtained. The PES crossing between the singlet and the triplet excited state is found. The intersystem crossing (ISC) is apt to take place at the isoenergy points in the excited state so that the high triplet quantum yield can be gained. A pronounced charge transfer executes in the H-chelate ring during the process of IHT of PQ. The dramatic charge transfer in the H-chelate ring is liable to induce magnetic field, which is essential to reverse electron spin during the ISC process.Conjugated structure has a vital effect on the IHT reaction of PQ and its similar molecules. As for the molecules with smaller conjugated structures, the singlet and triplet excited state potential energy profiles of IHT reaction separate from each other. The bigger the conjugated structure is, the closer these two potential energy profiles are. Considering PQ, there is an intersect... |
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