Untangling the excited states of DR1 in solution: an experimental and theoretical study.

We report the experimental observations and the theoretical predictions of the fully separated n-pi* and pi-pi* bands of Disperse Red One in acidified methanol solution. The analysis of the linear and two-photon absorption spectra is presented in four specific solvents. We demonstrate the possibility to establish the position of the first two excited states combining linear and nonlinear spectroscopy. Calculations using density functional theory at TD-B3LYP/6-31G*//HF/6-31G* level accurately predict the spectral region of the n-pi* and pi-pi* transitions of DR1 in all solvents.