Spectral shifts of the n → π* and π → π* transitions of uracil based on a modified form of solvent reorganization energy.

According to our recent studies on the nonequilibrium solvation, the solvent reorganization energy is found to be the cost of maintaining the residual polarization P', which equilibrates with the extra electric field E(ex). On the basis of this solvent reorganization energy and the well-established equilibrium solvation energy, a novel and reasonable expression for the spectral shift of the electronic absorption spectra is proposed in this work. Furthermore, the two lowest transitions of uracil in aqueous solution are investigated as test cases with the TDDFT/6-311++G** method. The obtained spectral shift is 0.48 eV for n → π* transition and -0.14 eV for π → π* transition, agreeing well with available experimental results. The contributions to the shift are discussed and the electrostatic plus polarization components are found to be crucial for the electronic absorption spectra of uracil in aqueous solution.