Near-infrared transient-absorption spectroscopy of zinc tetraphenylporphyrin and related compounds. Observation of bands that selectively probe the S-1 excited state

作者：Moravec Davis B; Lovaasen Benjamin M; Hopkins Michael D^*

来源：Journal of Photochemistry and Photobiology A: Chemistry , 2013, 254: 20-24.

DOI：10.1016/j.jphotochem.2012.12.025

• Pump-probe
• Near infrared
• Porphyrin
• Dark state
• Photophysics

Picosecond transient-absorption spectra are reported for the Si excited state of zinc tetraphenylporphyrin (ZnTPP) and related compounds in the near-infrared region (lambda <= 1400 nm). The spectra exhibit a prominent absorption band (epsilon congruent to 4400 M-1 cm(-1) for ZnTPP) between 1200 and 1300 nm whose position is sensitive to solvent (toluene and THF), zinc coordination number (ZnTPP(py-4-CCPh)), the metal center (GaTPP(Cl)), and the positions of the porphyrin substituents (zinc octaethylporphyrin, ZnOEP). The transient-absorption profile between 850 and 1200 nm is also sensitive to these variations. The near-infrared bands for the TPP compounds are assigned to transitions from the S-1 state to gerade-symmetry dark states based on their correspondence to relative energies predicted by previously reported time-dependent density functional theory calculations and their constant energy gap relative to the S-2 state. The characteristics of the prominent near-infrared transient-absorption band make it well suited for selectively probing photophysical and photoredox processes of the Si state because it does not overlap with absorption bands of the T-1 excited state or of [ZnTPP](+) or [ZnTPP](-), in contrast to the features in the typically probed visible-wavelength region.

• 出版日期2013-2-15