Nanosecond laser photolysis studies of chloropyridinato-and chloroaquachromium(III) tetraphenylporphyrin, ClCr III TPP(Py) and ClCr III TPP(H 2 O), dissolved in polystyrene films have been carried out in the temperature range 77-300 K. The transient observed for ClCr III TPP(Py) after laser pulsing is solely the excited states (the tripquartet, 4 T 1 , and tripsextet, 6 T 1 , states). The emission from the tripquartet state, 4 T 1, is detected upon laser excitation of ClCr III TPP(Py). No photodissociation of axial pyridine is detected in the temperature range studied. The laser photolysis of ClCr III TPP(H 2 O) in polystyrene films gives two transients; the excited states ( 4 T 1 and 6 T 1 ) of ClCr III TPP(H 2 O) and the five coordinate ClCr III TPP yielded by the photodissociation of axial H 2 O from ClCr III TPP(H 2 O). The yields of the excited states ( 4 T 1 and 6 T 1 ) for both ClCr III TPP(Py) and ClCr III TPP(H 2 O) were found to increase with a decrease in temperature. The lifetimes and the relative yields of the excited states and the relative yields of the photodissociation of the axial ligands were measured in the temperature range 77-300 K. These results lead to the conclusions that (1) the energy gaps between the 4 T 1 and 6 T 1 states are 1.5 and 1.1 kcal mol -1 for ClCr III TPP(Py) and ClCr III TPP(H 2 O), respectively, (2) the full photodissociation of axial H 2 O from ClCr III TPP(H 2 O) occurs from the singquartet state, 4 S 1 , and (3) the photodissociation of the axial ligand is the major pathway for excitation energy dissipation at the 4 S 1 state of six-coordinate chromium(III) porphyrin.

N,N′-Disalicylideneethylenediaminato)cobalt(II), Co II salen, and (N,N′-bis(1-methyl-3-oxobutylidene)ethylenediaminato)cobalt(II), Co II acacen, in both ethanol and toluene react with nitric oxide to give the nitric oxide adducts, (NO)Co II salen and (NO)Co II acacen. The laser photolysis studies revealed that (NO)Co II salen photodissociates NO to yield Co II salen with the quantum yields 1.0 ( 0.1 in ethanol and 0.6 ( 0.1 in toluene at 300 K. The transient product, Co II salen, undergoes the recombination reaction with NO to regenerate (NO)Co II salen with the rate constant 1.1 × 10 9 M -1 s -1 . The quantum yields, φ, for photodissociation of NO from (NO)Co II acacen are obtained as φ ) 1.0 ( 0.1 and φ < 0.01 in toluene and ethanol, respectively. The quantum yields φ for both (NO)Co II salen and (NO)Co II acacen are found to be markedly dependent on temperature: the yield decreases with a decrease in temperature. The photodissociation mechanism of NO from (NO)Co II salen and (NO)Co II acacen is discussed on the basis of the laser photolysis studies carried out in the temperature range 160-300 K. Bunsen absorption coefficients of NO in ethanol and toluene at 300 K were determined from kinetic analysis of the recombination reaction between NO and cobalt(II) Schiff bases.