The role of the internal rotation on the 5-benzyluracil excited states

The structure and barrier to internal rotation of 5-benzyluracil along the CH₂ bridge between the benzol and uracil molecular fragments in the ground state has been examined. The electronically excited S₁- and S₂-state has been calculated by time-dependent density functional level of theory using the B3LYP exchange-correlation functional with aug-cc-pVTZ basis set. The result shows significant energy level and oscillator strength shifts due to the internal rotation compared with the similar data in the equilibrium position. It was also found that there are several relative internally rotated geometry configurations where we obtain higher absortion probability of the excitation wavelength.