The morphology and optical properties of self-assembled porphyrin aggregates are sensitively dependent on solvent and other solution components. Building on previous work on tetrasulfonatophenylporphyrin (TSPP) aggregates induced by acids and salts in aqueous solution, we further explore the role of solvent hydrogen bonding by examining aggregates formed in ethanol. We use steady state fluorescence at several temperatures between 295 and 10 K to probe the structure of excitons giving rise to the Q bands and the interaction of these states with the stronger Soret band excitons. The Q band is found to consist of two major components (JQ and HQ) corresponding respectively to the J and H band components of the Soret region of the aggregate absorption spectrum (JB and HB). For the JQ component, fluorescence intensity increases as the temperature is decreased, as does the ratio of 0-0 to 0-1 vibronic components. The HQ component displays less pronounced trends with temperature. These results agree qualitatively with theoretical predictions for J- and H- aggregate luminescence in the literature (Spano, F.C.; Yamagata, H. J. Phys. Chem. B, 2011, 115, 5133). We connect these results to morphological properties observed by scanning probe microscopy. Additionally, dependence of these observations on solution acidity is related to differences in the excitonic structure of the Soret band region indicated by absorption and resonance Raman spectroscopy.

Excitonic structure and environment effects in porphyrin aggregates probed with low-temperature fluorescence

251st National Meeting (2016)

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