卤代对苝醌类光敏剂光敏活性影响的量子化学研究

Quantum Chemical Study on the Effect of HalogenSubstitution on Photosensitization of Perylenequinonoid Photosensitizer*

以一种新型的醌类光敏剂—菌生素 (HMB)为模型化合物 ,利用量子化学从头算HF/ 6 31G和含时密度泛函TD B3LYP/ 6 31G方法计算研究了卤代作用对醌类光敏剂分子性质和光敏活性的影响 .结果发现 ,卤代作用降低了HMB母体的HOMO和LUMO能级 (EHOMO和ELUMO)及其差值△E ,随卤族元素从上到下 ,EHOMO和ELUMO呈增大趋势 ,而△E呈减小趋势 ,使得分子激发光谱有不同程度的红移 ,在增加PQP三重态量子产率的同时降低了分子最低三重激发态的能量 ,两种作用相互抵消 ,使得卤代物的 1O2 量子产率与母体相似 ;增加了分子的绝热电子亲合势 ,使分子产生O2 -的能力下降 ;卤原子的引入 ,降低了HMB母体分子内氢键的强度 ,同时使顺式构型的分子内质子传递势垒增大 ,而使反式构型势垒减小 .

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 E_ HOMO and E_ LUMO, and the △E. From chlorine, bromine to iodine substitutes, the E_ HOMO and E_ LUMO increased, while the corresponding △E 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 1O_2 yields with their parent compounds. After halogen substitutions, the molecular adiabatic electron affinities increased, which made the substitutes possess lower O_2 --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.