Actinometry in Monochromatic Flash Photolysis: The Extinction Coefficient of Triplet Benzophenone and Quantum Yield of Triplet Zinc Tetraphenyl Porphyrin

摘要

The extinction coefficient epsilon/sub T/, of triplet benzophenone in benzene has been directly determined by absolute measurements of absorbed energy and triplet absorbance, delta D exp 0 /sub T/, under demonstrably linear conditions where incident excitation energy, E sub 0 , and ground state absorbance, A sub 0 , are both extrapolated to zero. The result, 7220 +- 320 M exp -1 cm exp -1 at 530 nm, validates and corrects many measurements of triplet and radical extinctions and yields, using the energy-transfer method. As E sub 0 and A sub 0 both decrease, delta D exp 0 /sub T/ becomes proportional to their product. In this situation, the ratio R = (1/A sub 0 ) (d delta D exp 0 /sub T//dE sub 0 ) = (epsilon/sub T/ exp - epsilon/sub G/)phi/sub T/. Measurements of R, referred to benzophenone, give (epsilon/sub T/ - epsilon/sub G/)phi/sub T/ for any substance, without necessity for absolute energy calibration. Both absolute and relative laser flash measurements on zinc tetraphenyl porphyrin (epsilon/sub T/ - epsilon/sub G/ at 470 nm = 7.3 x 10 exp 4 M exp -1 cm exp -1 ) give phi/sub T/ = 0.83 +- 0.04. 6 figures, 2 tables. (ERA citation 08:018360)