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Updated: Nov 18, 2025

Isotopic Effect in Double Proton Transfer Process of Porphycene Investigated by Enhanced QM/MM Method
Published on: July 19, 2019
Controlling Emissive Properties by Intramolecular Hydrogen Bonds: Alkyl and Aryl meso-Substituted Porphycenes
Arkadiusz Listkowski1,2, Natalia Masiera1, Michał Kijak1
1Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224, Warsaw, Poland.
Abstract:
Porphycene, a porphyrin isomer, is an efficient fluorophore. However, four-fold meso substitution with alkyl groups decreases the fluorescence quantum yield by orders of magnitude. For aryl substituents, this effect is small. To explain this difference, we have synthesized and studied a mixed aryl-alkyl-substituted compound, 9,20-diphenyl-10,19-dimethylporphycene, as well as the 9,20-diphenyl and 9,20-dimethyl derivatives. Analysis of the structural, spectroscopic, and photophysical data of the six porphycenes, combined with quantum chemical calculations, shows a clear correlation between the strength of the intramolecular NH⋅⋅⋅N hydrogen bonds and the efficiency of the radiationless depopulation of the lowest-excited singlet state. This result led us to propose a model in which the delocalization of the inner protons in the cavity of the macrocycle is responsible for the nonradiative deactivation channel. The applicability of the model is confirmed by the literature data for other alkyl- or aryl-substituted porphycenes. The finding of a correlation between structural and emissive characteristics enables a rational design of porphycenes with desired photophysical properties.
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