Vibronic spectroscopy of the H-bonded aminophenol–water complex

Abstract

In this work, the vibronic spectroscopy of the p-aminophenol–water 1:1 complex is presented. The S1 vibrational energy levels of the complex were characterized by REMPI spectroscopy up to 2500 cm−1 above the band origin. The dispersed fluorescence spectra were recorded for the B.O., 6a01 and I02 excitations to characterize the vibrational levels in the S0 state of the complex. Stimulated ion depletion spectroscopy was carried out to determine the higher vibrational levels of the ground state all the way up to ∼3075 cm−1. The structure and the vibrational levels of the AP–W1 complex were calculated ab initio at the HF level and DFT with B3LYP functional for S0, and CIS level for S1 using 6-31G** basis set. The structure of the AP–W1 complex compared well with the earlier calculations for this case as well as the other ROH–water (R=aromatic group) complexes reported in the literature. However, the redshift in the electronic band origin was almost half of that observed in other cases. A good correlation was shown to exist between the electronic red shifts and the respective pKa* values (the pKa in the excited state).