Nastasi Francesco, La Ganga Giuseppina, Campagna Sebastiano, Syrgiannis Zois, Rigodanza Francesco, Vitale Stefania, Licciardello Antonino, Prato Maurizio
Dipartimento di Scienze Chimiche, Biologiche, Farmaceutiche ed Ambientali, Università di Messina, e Centro di ricerca Interuniversitario per la Conversione Chimica dell'Energia Solare (SOLAR-CHEM), 98166 Messina, Italy.
Phys Chem Chem Phys. 2017 May 31;19(21):14055-14065. doi: 10.1039/c7cp01597f.
Herein, the synthesis and the photophysical and redox properties of a new perylene bisimide (PBI) species (L), bearing two 1,10-phenanthroline (phen) ligands at the two imide positions of the PBI, and its dinuclear Ru(ii) and Os(ii) complexes, (bpy)Ru(μ-L)Ru(bpy) (Ru2; bpy = 2,2'-bipyridine) and (Me-bpy)Os(μ-L)Os(Me-bpy) (Os2; Me-bpy = (4,4'-dimethyl)-2,2'-bipyridine), are reported. The absorption spectra of the compounds are dominated by the structured bands of the PBI subunit due to the lowest-energy spin-allowed π-π* transition. The spin-allowed MLCT transitions in Ru2 and Os2 are inferred by the absorption at 350-470 nm, where the PBI absorption is negligible. The absorption band extends towards the red region for Os2 due to the spin-forbidden MLCT transitions, intensified by the heavy osmium center. The reduction processes of the compounds are dominated by two successive mono-electronic PBI-based processes, which in the metal complexes are slightly shifted compared to the free ligand. On oxidation, both metal complexes undergo an apparent bi-electronic process (at 1.31 V vs. SCE for Ru2 and 0.77 V for Os2), attributed to the simultaneous one-electron oxidation of the two weakly-interacting metal centers. In Ru2 and Os2, the intense fluorescence of L subunit (λ, 535 nm; τ, 4.3 ns; Φ, 0.91) is fully quenched, mainly by photoinduced electron transfer from the metal centers, on the ps timescale (time constant, 11 ps in Ru2 and 3 ps in Os2). Such photoinduced electron transfer leads to the formation of a charge-separated state, which directly decays to the ground state in about 70 ps in Os2, but produces the triplet π-π* state of the PBI subunit in 35 ps in Ru2. The results provide information on the excited-state processes of the hybrid species combining two dominant classes of chromophore/luminophore species, the PBI and the metal polypyridine complexes, and can be used for future design on new hybrid species with made-to-order properties.
本文报道了一种新型苝二酰亚胺（PBI）化合物（L）及其双核钌（II）和锇（II）配合物（bpy）Ru（μ-L）Ru（bpy）（Ru2；bpy = 2,2'-联吡啶）和（Me-bpy）Os（μ-L）Os（Me-bpy）（Os2；Me-bpy = （4,4'-二甲基）-2,2'-联吡啶）的合成、光物理和氧化还原性质。由于最低能量的自旋允许π-π跃迁，化合物的吸收光谱主要由PBI亚基的结构化谱带主导。Ru2和Os2中自旋允许的MLCT跃迁可通过350 - 470 nm处的吸收推断，此处PBI的吸收可忽略不计。由于自旋禁阻的MLCT跃迁，Os2的吸收带向红色区域延伸，重原子锇中心使其增强。化合物的还原过程由两个连续的基于PBI的单电子过程主导，在金属配合物中与游离配体相比略有位移。氧化时，两种金属配合物都经历一个明显的双电子过程（Ru2相对于饱和甘汞电极（SCE）为1.31 V，Os2为0.77 V），这归因于两个弱相互作用金属中心同时进行的单电子氧化。在Ru2和Os2中，L亚基强烈的荧光（λ，535 nm；τ，4.3 ns；Φ，0.91）在皮秒时间尺度上（Ru2的时间常数为11 ps，Os2为3 ps）主要通过从金属中心的光诱导电子转移而完全猝灭。这种光诱导电子转移导致形成电荷分离态，在Os2中约70 ps直接衰减到基态，但在Ru2中35 ps产生PBI亚基的三重态π-π态。这些结果提供了关于结合两种主要发色团/发光团物种（PBI和金属多吡啶配合物）的杂化物种激发态过程的信息，可用于未来定制性质的新型杂化物种的设计。
