Spectroscopic characterization of α- and γ-pyrones and their substituted 4-hydroxy and 4-methoxy derivatives: an integrated infrared, photophysical and theoretical study

Abstract

The simple α- and γ-pyrones and the substituted 6-methyl, 4-hydroxy and 4-methoxy α-pyrones were investigated in relation to their spectroscopic properties. The characterization involves vibrational and electronic spectroscopy. IR spectra for the ground electronic state of the studied compounds at room temperature were obtained and interpreted taking into consideration the simulated ab initio (6-31G∗) data. The most important canonical structures accounting for the properties of the ground state were determined for each compound and several photophysical properties were evaluated: electronic spectra, oscillator strengths and the emission properties (both fluorescence and phosphorescence) in media of different polarity. The origin of the first singlet and triplet excited states is also discussed. In addition, the energies of the electronic transitions were estimated using semi-empirical molecular orbital calculations, the calculated results showing an excellent agreement with the experimental data.