Photophysics of Self-Assembled Zinc Porphyrin−Bidentate Diamine Ligand Complexes

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 114; no. 41; pp. 10960 - 10968
• Main Authors: Danger, Brook R, Bedient, Krysta, Maiti, Manisankar, Burgess, Ian J, Steer, Ronald P
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 21.10.2010
• Subjects: A: Kinetics, Spectroscopy
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp106809j

The effects of complexationby bidentate nitrogen-containing ligands such as pyrazine and 4,4′-bipyridine commonly used for porphyrin self-assemblyon the photophysics of the model metalloporphyrin, ZnTPP, are reported. Ligation to form the 5-coordinate species introduces an intramolecular charge transfer (ITC) state that, depending on the oxidation and reduction potentials of the electron donor and acceptor, can become involved in the excited state relaxation processes. For ZnTPP, ligation with pyridine has little effect on excited state relaxation following either Q-band or Soret band excitation. However, coordination of ZnTPP with pyrazine and bipyridine causes the S2 (Soret) state of the ligated species to decay almost exclusively via an S2−ICT−S1 pathway, while affecting the S1 decay route only slightly. In these 5-coordinate species the S2−ICT−S1 decay route is ultrafast and nearly quantitative. Literature redox data for other bidentate ligands such as DABCO and multidentate ligands commonly used for pophyrin assembly suggest that the ITC states introduced by them could also modify the excited state relaxation dynamics of a wide variety of multiporphyrin arrays.