THE APPLICATION OF THE ENERGY-GAP LAW TO THE S-1 ENERGIES AND DYNAMICS OF CAROTENOIDS

The energy gap law for radiationless transitions set forth by Englman and Jortner (Mel. Phys. 18 (1970) 145) has been evaluated for use in deducing the S-1 energies of carotenoids. A simultaneous knowledge of the dynamics and energies of the S-1 states of carotenoids are available for only a few of these molecules owing to the lack of detectable S-1 state fluorescence in many cases. All the available data where the S-1 dynamics and energetics of carotenoids are simultaneously known were fit by the energy gap law expression in its full exponential form. The parameters derived from the computer optimization suggest that the weak coupling limit form of the energy gap law is valid for describing the relationship between the dynamics and energetics of carotenoid molecules. The optimal fitting parameters were then used in conjunction with the energy gap law expression to calculate the S-1 energies of several biologically important carotenoids from the lifetimes of their S-1 states. Particularly important is the S-1 energy of beta-carotene determined in this analysis to be 14100 cm(-1).