The addition of arylethynyl groups to the porphyrin macrocycle represents an effective strategy with which to enhance the light-harvesting properties of porphyrins. We recently showed that enhanced substituent effects on porphyrin absorption spectra are observed in arylethynyl porphyrins relative to meso-tetraphenylporphyrin (H2TPP) derivatives owing to the presence of ethynyl spacers. We now extend this work to arylethynyl porphyrins with two or four p-hydroxyphenyl substituents. Upon deprotonation of the peripheral hydroxyphenyl substituents, spectral features are substantially red-shifted and oscillator strengths in the Q-band region increase dramatically. Such spectral features have been previously characterized as “hyperporphyrin spectra” and are indicative of excited state charge-transfer character. When the hydroxyphenyl groups are appended to the porphyrin macrocylce via the ethynyl spacers, the spectral shifts observed upon deprotonation are significantly enhanced relative to those observed for substituted H2TPP derivatives, highlighting the role of expanded conjugation in altering porphyrin photophysics.

Spectroscopic characterization of free-base bis(arylethynyl)porphyrins bearing p-hydroxyphenyl substituents

249th National Meeting (2015)

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Spectroscopic characterization of free-base bis(arylethynyl)porphyrins bearing p-hydroxyphenyl substituents<br />