We have used action photofragmentation spectroscopy in the visible spectral range (410 to 650 nm) to investigate the optical properties of different monomeric and dimeric M^(II)-meso-tetra-(4-sulfonatophenyl)-porphyrin (with M = Pd(II), Cu(II), Zn(II)) multianions isolated in the gas phase without solvent. In particular, we report the position of the Q-bands (S₀ → S₁ transitions) as a function of charge state, counterions, oligomerization, and dimer structure type. The results for the monomers (charge states = 4– and 3–, sodiated and protonated) are in good agreement with TDDFT calculations and condensed-phase spectra. For both homo and heterometallic dimers, photofragmentation spectra were recorded for two charge states, 5– and 3–, corresponding to coplanar and cofacial structure types, respectively. The fragmentation patterns observed for the dimers depend significantly on charge state, with fragmentation into monomers being dominant for the 5– species, while the 3– charge state predominantly fragments by SO₂ loss. The monomer → dimer Q-band spectral shifts observed in the gas phase were compared with the optical properties of porphyrin aggregates in solution.

中文翻译：

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游离金属卟啉二聚体多阴离子的光解离

我们已经使用可见光光谱范围（410至650 nm）中的作用光碎裂光谱技术研究了不同的单体和二聚体M ^（II） -meso-tetra-（4-sulfonatophenyl）-porphyrin（其中M = Pd（II ），Cu（II），Zn（II））多阴离子在没有溶剂的情况下在气相中分离。特别是，我们报告了Q波段的位置（S ₀ →S ₁过渡）作为电荷状态，抗衡离子，低聚和二聚体结构类型的函数。单体的结果（电荷态分别为4–和3–，已磺化和质子化）与TDDFT计算和凝聚相光谱非常吻合。对于均质和异金属二聚体，记录了两种电荷状态5–和3–的光碎裂光谱，分别对应于共面和共面结构类型。观察到的二聚体的碎裂模式在很大程度上取决于电荷状态，其中以5–种为主体的碎裂为单体，而以3–电荷状态为主的SO ₂损失碎裂。将气相中观察到的单体→二聚体Q带光谱位移与溶液中卟啉聚集体的光学性质进行了比较。