Electronic structure, spectra and excited state properties of N, N-dimethylaminoguanine

Abstract

An experimental and ab initio theoretical study has been performed on the electronic spectra and structure of N, N-dimethylaminoguanine (DMAG). The experimental work included study of absorption and fluorescence spectra at different pH in aqueous solution while the theoretical study included SCF-CIS ab initio gas phase computations of ground and excited state geometries and electronic transitions of the molecule. Vertical transitions from the optimised ground state of the molecule were also studied theoretically under solvation in water using the polarized continuum model (PCM). It has been shown that at the neutral and acidic pH (∼3), the molecule would exist in the ground state in the keto-N 9H form while at alkaline pH (∼11), it would mainly occur in the anionic form deprotonated at the N 9 site. Further, the molecule seems to get deprotonated in the lowest singlet π– π* excited state even at the neutral pH. Molecular electrostatic potential mapping was performed in the ground and lowest two singlet excited states of the keto-N 9H form of the molecule in order to study the mechanism of its phototautomerism to the keto-N 7H form which appears to be important from the point of view of fluorescence.