Photophysics of “Porphyrin Cages”: Absorption and Emission Spectroscopy

This study explores the optical properties of porous porphyrin cages through the use of spectroscopic techniques. The findings reveal that cages featuring electron-donating nitrogen functional groups display distinct alterations in their absorption spectra, including a red-shift and broadening of Soret bands, and a decrease in the Soret:Q-band ratio. The extent of conjugation within the cages significantly impacts their molar absorptivity, demonstrating a linear correlation with the number of saturated cage linkages and a superlinear increase for highly conjugated cages. The emission spectra of the cages largely mirror that of the monomer, barring fully conjugated cages. The relative fluorescence quantum yields differ among the cages, with some showing enhancements and others reductions, likely due to variations in cage rigidity. Time-resolved emission measurements indicate that the number of porphyrins in the cages affects the emission lifetime, with increased conjugation resulting in a shorter lifetime due to exciton delocalization. These insights underscore the potential of highly conjugated cages in optoelectronic devices, photosensitizers, and photocatalysts, given their effective light absorption and energy distribution capabilities.