Effect of Solvent Polarity on the Spectral Characteristics of 5,10,15,20-Tetrakis(p-hydroxyphenyl)porphyrin

The electronic absorption and vibrational spectra of deprotonated 5,10,15,20-tetrakis(p-hydroxyphenyl)porphyrin (THPP) are studied as a function of solvent polarity in H2O-DMF, H2O-acetone, H2O-methanol, and DMF-acetone mixtures. The maximum absorption wavelength (& lambda;(max)) of the lowest energy electronic absorption band of deprotonated THPP shows an unusual solvatochromism-a bathochromic followed by a hypsochromic shift with reduced polarity. According to the correlation analysis, both specific interactions (H-bonds) and nonspecific interactions affect the spectral changes of this porphyrin. Furthermore, the solvent polarity scale E-T(30) can explain both shifts very well. At higher polarity (E-T(30) > 48), THPP exists as a hyperporphyrin. The E-T(30) is linear with & lambda;(max) and a decrease in solvent polarity is accompanied by a bathochromic shift of & lambda;(max). These results can be rationalized in terms of the cooperative effects of H-bonds and nonspecific interactions on the spectra of hyperporphyrin. At relatively low polarity (45.5 < E-T(30) < 48), hyperporphyrin gradually becomes Na2P as E-T(30) reaches the critical value of 45.5. The spectrum of the hyperporphyrin turns into the three-band spectrum of the metalloporphyrin, which is accompanied by a hypsochromic shift of & lambda;(max).

Automated summary

The electronic absorption and vibrational spectra of deprotonated 5,10,15,20-tetrakis(p-hydroxyphenyl)porphyrin (THPP) were studied as a function of solvent polarity in various solvent mixtures. The absorption spectrum of deprotonated THPP showed an unusual solvatochromism, with a bathochromic shift followed by a hypsochromic shift with reduced solvent polarity. The shifts in spectrum could be explained by the cooperative effects of specific interactions (H-bonds) and nonspecific interactions, as well as the solvent polarity scale E-T(30).