The developments in porphyrin chemistry over the last decades give great advantages for the practical use of porphyrin-based compounds. The properties of these compounds can be systematically tuned by rational utilization of substituents on meso- and/or β-positions as well as by using different metal atoms in the center of the tetrapyrrole macrocycle. Recently we prepared novel mono- and bis-functionalized cycloketo-porphyrins (CKPors). In this work the results of detailed spectroscopic investigations of these compounds are presented. It was found that a seven-membered ketone exocycle remarkably influences the photophysical properties of the CKPor systems. For mono-functionalized CKPors it results in strongly enhanced probability of intersystem crossing S₁ → T₁ with an ISC quantum yield up to 90%. Moreover, the absorption of all CKPors undergoes a bathochromic shift and the Q-bands extinction is above two times higher compared to that of H₂TPP, what makes these compounds promising candidates for use as photosensitizers in photodynamic therapy of tumors. For the first time two NH-tautomers of nonsymmetrical CKPors were experimentally resolved at room temperature using optical spectroscopic methods. It was found that the concentration of tautomer A with a lower frequency of the S_0,0 → S_1,0 transition is higher than that one of tautomer B at room temperature, and becomes dominant with cooling down. In contrast - and as it is expected - only one optical active species was observed for non-symmetrical CKPor with a central Zn(II) atom as well as for symmetrical bis-CKPor.

Date Published: 2 September 2008
PDF: 11 pages
Proc. SPIE 7049, Linear and Nonlinear Optics of Organic Materials VIII, 704905 (2 September 2008); doi: 10.1117/12.793356

Published in SPIE Proceedings Vol. 7049:
Linear and Nonlinear Optics of Organic Materials VIII
Rachel Jakubiak, Editor(s)