三氟乙酸对无金属卟啉-苝酰亚胺分子阵列激发态衰变过程的影响

Effect of CF_3COOH on Decay Mechanism of the Excited State of a Free-base-Porphyrin-Perylene-Diimide Array

用紫外 -可见吸收光谱和荧光光谱研究了 CF3COOH浓度变化对 CHCl3溶液中 N -[p-5′-( m-1 0′,1 5′,2 0′-三苯基卟啉 )基 ]-N′-正十二烷基 -3 ,4∶ 9,1 0 -四羧基二酰亚胺分子阵列 ( Tr PP-MDPTCDI)的光致激发态衰变机理的影响 ,发现无论激发无金属卟啉还是酰亚胺基元 ,分子阵列均表现出质子化无金属卟啉生色团的特征荧光发射 .对电子结构的分析说明质子化使 [H2 + 2 Tr PP* -MDPTCDI]成为各种激发态中相对稳定的物种 ,因此 ,未质子化前占主导的从卟啉到酰亚胺基元的光致电子转移衰变途径在质子化后受到有效抑制 ,激发卟啉生色团 (λ=43 9nm)直接得到 [H2 + 2 Tr PP* -MDPTCDI],并以辐射衰变方式回到基态 ;激发酰亚胺生色团 ( λ=491 nm)得到的 [H2 + 2 Tr PP-MDPTCDI* ]通过电荷分离态迅速弛豫到 [H2 + 2 Tr PP* -MDPTCDI],并辐射荧光 ,同时伴随少量的从酰亚胺到质子化无金属卟啉生色团的能量转移 .

The effects of CF 3COOH concentration on the decay mechanism of a photo-excited free-base-porphyrin-perylene-diimide molecular array(TrPP-MDPTCDI) were investigated with UV-visible absorption spectroscopy and fluorescence spectroscopy. The data revealed that, the molecular array gave off a characteristic emission from the protonated free-base porphyrin upon the photo-excitation of both porpyrin and perylene-diimide subuntits. Based on the electronic structure, the protonation allowed the [H 2+ 2TrPP*-MDPTCDI] to be relatively stable in all the photo-excited species. As a result, the electron transfer from free-base-porpyrin to perylene-diimide, a predominate decay channel in the absence of CF 3COOH was effectively inhibited, and the [H 2+ 2TrPP*-MDPTCDI] formed upon the excitation of protonated free-base porphyrin (λ=438 nm) relaxed directly to the ground state with fluorescence; while the [H 2+ 2TrPP-MDPTCDI*] formed upon the excitation of perylene-diimide subunit (λ=491 nm) relaxed via a charge-separation mediate species to [H 2+ 2TrPP*-MDPTCDI], which decayed with radiation of protonated free-base porpyrin; the latter course was accompanied with a low efficiency energy transfer from perylene-diimide to the protonated free-base porphyrin subunit.