Macrocyclic complexes of the type trans-[Cr(N-4)(CN)(2)](+), where N-4 = cyclam, 1,11 -C-3-cyclam, and 1,4-C-2-cyclam\ demonstrate significant variation in their room-temperature excited-state behavior; namely, the lifetimes of the E-2(g) (O-h) excited states are 335, 23, and 0.24 mu s, respectively. The lifetimes of these complexes have been measured in acidified H2O/dimethyl sulfoxide over the temperature range between -30 and +95 degrees C. Arrhenius activation parameters were calculated from these data. There was very little variation in the values of the Arrhenius preexponential factor between these three complexes, whereas the value of E-a is 40.6 kJ/mol for the cyclam complex, 35.5 kJ/mol for the 1,11-C-3-cyclam complex, and 22.3 kJ/mol for the 1,4-C-2-cyclam complex. Thus, differences in the room-temperature excited-state lifetimes can be rationalized based on the competition between thermally independent nonradiative relaxation and a thermally activated channel. To test whether a photodissociation mechanism involving Cr-macrocyclic N bond cleavage is a plausible explanation for the thermally activated relaxation pathway, samples of the cyclam complex were photolyzed in acidified D2O. A marked increase in the lifetime after photolysis demonstrated the occurrence of photodeuteration and thus a likely photodissociation of a macrocyclic N.