Photochemical hole burning in higher excited states (Soret absorption bands) of tetrabenzo- and tetraphenylporphins

Abstract

We report first results on photochemical spectral hole burning in the Soret absorption bands of zinc-tetratolyltet-rabenzoporphin (ZnTTBP), free-base and zinc-tetraphenylporphins (H 2TPP and ZnTPP) in poly(methylmethacrylate) and poly(chloromethylstyrene). In case of ZnTTBP narrow zero-phonon holes are formed throughout the whole Soret band, proving inhomogeneous broadening of the band. Electron-phonon coupling in both first S 1 and second S 2 excited singlet states is shown to be equal; the Huang-Rhys factor is 0.15. Zero-phonon hole width yields the second excited state lifetime of 1.7 ps at 20 K. Strong correlation between S 0-S 1 and S 0-S 2 transitions was observed with the correlation coefficient p = 0.981. In case of H 2TPP and ZnTPP only broad holes are observed whose widths are comparable to the absorption bandwidths. The corresponding electronic relaxation times at 20 K are in the sub-picosecond region.