On the Theory of 3-Methyl Lumiflavin in Solution

Abstract

The absorption spectrum of 3-methyl lumiflavin in solution is reexamined by our previous formulation for π-electron systems, improving the previous estimation of the ratio of oscillator strength of the second to the first absorption band. It is found that the following two screenings are necessary to reproduce the absorption spectrum in benzene: (1) the screening of two-center Coulomb repulsion integrals for all the pairs of atoms except bonded ones; (2) that of the effective nuclear charges Z′ determined by Julg’s method for Slater-type 2p_z-orbitals. It is also found that the absorption spectrum in ethanol or water can be explained by the model of 3-methyl lumiflavin interacting with two point-dipoles. The angle between the transition moments of the first and second bands is found to be at most 44.4° in benzene, 44.3° in ethanol and 45.8° in water.