Fukuzumi Shunichi, Ohkubo Kei, Ortiz Javier, Gutiérrez Ana M, Fernández-Lázaro Fernando, Sastre-Santos Angela
Department of Material and Life Science, Graduate School of Engineering, Osaka University, SORST, Japan Science and Technology Agency (JST), Suita, Osaka 565-0871, Japan.
J Phys Chem A. 2008 Oct 30;112(43):10744-52. doi: 10.1021/jp805464e. Epub 2008 Oct 4.
Photoexcitation of a zinc phthalocyanine-perylenediimide (ZnPc-PDI) dyad and a bis(zinc phthalocyanine)-perylenediimide [(ZnPc) 2-PDI] triad results in formation of the triplet excited state of the PDI moiety without the fluorescence emission, whereas addition of Mg (2+) ions to the dyad and triad results in formation of long-lived charge-separated (CS) states (ZnPc (+)-PDI (-)/Mg (2+) and (ZnPc) 2 (+)-PDI (-)/Mg (2+)) in which PDI (-) forms a complex with Mg (2+). Formation of the CS states in the presence of Mg (2+) was confirmed by appearance of the absorption bands due to ZnPc (+) and PDI (-)/Mg (2+) complex in the time-resolved transient absorption spectra of the dyad and triad. The one-electron reduction potential ( E red) of the PDI moiety in the presence of a metal ion is shifted to a positive direction due to the binding of Mg (2+) to PDI (-), whereas the one-electron oxidation potential of the ZnPc moiety remains the same. The binding of Mg (2+) to PDI (-) was confirmed by the ESR spectrum, which is different from that of PDI (-) without Mg (2+). The energy of the CS state (ZnPc (+)-PDI (-)/Mg (2+)) is determined to be 0.79 eV, which becomes lower that of the triplet excited state (ZnPc- (3)PDI*: 1.07 eV). This is the reason why the long-lived CS states were attained in the presence of Mg (2+) instead of the triplet excited state of the PDI moiety.
锌酞菁 - 苝二酰亚胺（ZnPc - PDI）二元体系和双（锌酞菁） - 苝二酰亚胺[（ZnPc）₂ - PDI]三元体系的光激发会导致苝二酰亚胺（PDI）部分形成三重激发态且无荧光发射，而向二元体系和三元体系中添加Mg²⁺离子会导致形成长寿命的电荷分离（CS）态（ZnPc（⁺） - PDI（⁻）/Mg²⁺和（ZnPc）₂（⁺） - PDI（⁻）/Mg²⁺），其中PDI（⁻）与Mg²⁺形成络合物。在二元体系和三元体系的时间分辨瞬态吸收光谱中，由于ZnPc（⁺）和PDI（⁻）/Mg²⁺络合物出现吸收带，从而证实了在Mg²⁺存在下CS态的形成。由于Mg²⁺与PDI（⁻）结合，金属离子存在下PDI部分的单电子还原电位（Ered）向正方向移动，而ZnPc部分的单电子氧化电位保持不变。Mg²⁺与PDI（⁻）的结合通过电子顺磁共振（ESR）光谱得到证实，该光谱与不含Mg²⁺的PDI（⁻）的光谱不同。CS态（ZnPc（⁺） - PDI（⁻）/Mg²⁺）的能量测定为0.79 eV，低于三重激发态（ZnPc - ³PDI*：1.07 eV）的能量。这就是为什么在Mg²⁺存在下获得了长寿命的CS态而非PDI部分的三重激发态的原因。
