Photophysical consequences of porphyrin tautomerization. Steady-state and time-resolved spectral investigations of a zinc isoporphyrin
- Washington Univ., St. Louis, MO (United States)
- Univ. of California, Davis, CA (United States)
- Brookhaven National Lab., Upton, NY (United States)
Isoporphyrins are porphyrin tautomers with a saturated meso carbon and thus an interrupted {pi} system. We report here steady-state optical absorption, fluorescence, and fluorescence polarization data as well as time-resolved results that detail the significant effects of porphyrine tautomerization on the photophysical properties of a metallo-isoporphyrin, zinc 2,3,5,5{prime},7,8,12,18-octamethyl-13,17-bis(3-methoxy-3-oxop ropyl) isoporphyrin perchlorate (2). Besides the red-shifted, low-energy absorption bands diagnostic of metallo-isoporphyrins, 2 exhibits a large Stokes shift of its fluorescence emission (approximately 600 cm{sup {minus}1}) and an unusually short singlet excited-state lifetime at room temperature (130 {+-} 15 ps), photophysical properties distinctly different from those of the canonical prophyrin tautomers. The only porphyrins to exhibit marginally similar perturbations of their photophysical properties are those with severely nonplanar macrocyles whose {pi} systems are significantly destabilized by the conformational distortions and thus approach the interrupted {pi} systems of isoporphyrins. In addition to providing the first insights into the photophysical consequences of porphyrin tautomerization, the results for the isoporphyrin further document the sensitivity of the fundamental electronic and excited-state properties of porphyrinic chromophores to modulation of their {pi} systems in vitro and, by extrapolation, in vivo as well. 28 refs., 4 figs.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States)
- DOE Contract Number:
- AC02-76CH00016
- OSTI ID:
- 35454
- Journal Information:
- Journal of Physical Chemistry, Vol. 99, Issue 12; Other Information: PBD: 23 Mar 1995
- Country of Publication:
- United States
- Language:
- English
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