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Thermodynamics and Photodynamics of a Monoprotonated Porphyrin Directly Stabilized by Hydrogen Bonding with Polar Protic Solvents
Author(s) -
Suzuki Wataru,
Kotani Hiroaki,
Ishizuka Tomoya,
Ohkubo Kei,
Shiota Yoshihito,
Yoshizawa Kazunari,
Fukuzumi Shunichi,
Kojima Takahiko
Publication year - 2017
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201606012
Subject(s) - chemistry , flash photolysis , photochemistry , hydrogen bond , acetonitrile , photoinduced electron transfer , electron transfer , protonation , porphyrin , molecule , reaction rate constant , kinetics , organic chemistry , ion , physics , quantum mechanics
Addition of 1 equiv of TFA to an acetone solution containing dodecaphenylporphyrin (H 2 DPP) in the presence of 10 % MeOH (v/v) resulted in selective formation of a monoprotonated form (H 3 DPP + ), in sharp contrast to protonation of H 2 DPP directly affording a diprotonated form (H 4 DPP 2+ ) in acetone in the absence of MeOH. The crucial role of MeOH for selective H 3 DPP + formation was interpreted as hydrogen‐bonding stabilization of H 3 DPP + , since a MeOH molecule was found to form hydrogen bonds with an NH proton of H 3 DPP + in the crystal. The selectivity of H 3 DPP + formation was evaluated by the formation yield of H 3 DPP + , which increased when elevating the portion of MeOH (0–10 %) in acetone with saturation behavior, suggesting that H 3 DPP + is stabilized by hydrogen bonding with MeOH even in solution, together with the thermodynamic parameters determined from a van't Hoff plot based on the spectroscopic titration. Femto‐ and nanosecond laser flash photolysis allowed us to elucidate the photodynamics of H 3 DPP + in intermolecular photoinduced electron transfer (ET) from ferrocene derivatives as one‐electron donors to the triplet excited state of H 3 DPP + as an electron acceptor. The second‐order rate constants of the ET reactions were evaluated in light of the Marcus theory of ET. The reorganization energy of ET was determined to be 1.87 eV, which is slightly larger than that of H 4 DPP 2+ in acetonitrile (1.69 eV), due to larger structural change upon ET than that of H 4 DPP 2+ .