Excited States of Porphyrin Macrocycles

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• 作者：Laura Moroni ; Cristina Gellini ; Pier Remigio Salvi Agnese MarcelliPaolo Foggi
• 刊名：Journal of Physical Chemistry A
• 出版年：2008
• 出版时间：November 6, 2008
• 年：2008
• 卷：112
• 期：44
• 页码：11044-11051
• 全文大小：255K
• 年卷期：v.112,no.44(November 6, 2008)
• ISSN：1520-5215

文摘

S₁ → S_n spectra of porphyrin, diprotonated porphyrin, and tetraoxaporphyrin dication have been measured in the energy range 2−3 eV above S₁ at room temperature in solution by means of transient absorption spectroscopy exciting with femtosecond pulses. Highly excited ππ* states not active in the conventional S₀ → S_n spectrum have been observed. The experimental data are discussed on the basis of the time dependent density functional theory taking advantage of large scale calculations of configuration interaction between singly excited configurations (DF/SCI). The DF/SCI calculation on porphyrin has allowed to assign g states active in the S₁ → S_n spectrum. Applying the same calculation method to tetraoxaporphyrin dication the S₀ → S_n spectrum is reproduced relatively to the Q and B (Soret) bands as well as to the weaker E_u bands at higher energy. According to our calculation the S₁ → S_n transient spectrum is related to states of g symmetry mainly arising from excitations between doubly degenerate π and π* orbitals such as 2e_g → 4e_g. In the case of diprotonated porphyrin it is shown that the complex of the macrocycle with two trifluoroacetate anions plays a significant role for absorption. Charge transfer excitations from the anions to the macrocycle contribute to absorption above the Soret band, justifying the intensity enhancement of the S₀ → S_n spectrum with respect to the other two macrocyclic systems.