Photophysics of\n“Porphyrin Cages”: Absorption\nand Emission Spectroscopy

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