Substituent effect on the intramolecular hydrogen bond and the proton transfer process in pyrimidine azo dye : A computional study

This study provides a complete analysis of the electronic and photophysical properties of, the derivative of uracil, IsoOrotic (IOA) azo dyes. The ability of the dye to work as an excited state intramolecular proton transfer (ESIPT) was investigated by using Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TDDFT) methods. The effect of electron-donating substituents (CH3 and NMe2) and an electron-withdrawing one (NO2) was examined. In addition, the effect of the solvent polarity on the ESIPT process is studied. All the geometrical structures in the singlet ground (S0) and excited (S1) states, were optimized using B3LYP/6-311 + G** level of theory. The intramolecular hydrogen bond parameters (IHBs), and the Infra-Red vibrational analysis of the O-H bond show that the IHBs are enhanced in the S1 state. Furthermore, the absorption and emission spectra were simulated and the values of stokes shifts were observed. The PAIOA derivative with an electron withdrawing group shows large stokes shift compared with those having electron-donating ones. Therefore, we can safely conclude that the substituent groups and the different solvents are extremely impactful on the ESIPT process.