Theory of the 3-Methyl Lumiflavin in Solution

The optical absorption of 3-methyl lumiflavin in solution is examined within the framework of π-electron approximation, according to our previous formulation of LCAO-ASMO-SCF-CI calculation. It is thus found that the absorption spectrum of 3-methyl lumiflavin observed in benzene can be reproduced only when the screening of two-center Coulomb repulsion integrals is taken into account for all the pairs of atoms except bonded ones. It is also found that the absorption spectra observed in ethanol or water can be explained by the model interacting with (i) two point-dipoles or (ii) a point-dipole and a point-charge, although the model (ii) is higher in ground-state energy than the model (i) by amount of 3.64 or 5.24 eV in the case of ethanol or water, respectively.