Comparative sensibility of S1 ←S0 and S2 ←S0 indole electronic transitions to environment perturbations. The positions of the 0—0 bands in polar media

The modifications under environmental perturbations of the well separated two first electronic systems of carbazole are used to demonstrate the possibility of including solute-ether complexes in polyethylene films. The application of this technique to indole allows to differentiate the overlapping ¹L_a and ¹L_b transitions in the spectrum of hydrogen bonded indole. The ground state interactions of indole, 5-methoxyindole and 3-methylindole in several well defined environment conditions (hydrogen bond in a polar cage, hydrogen bond in a nonpolar cage) are investigated through UV absorption spectroscopy between 293 and 88 K. A strong red shift of the ¹L_a bands under the hydrogen bonding occurs with all the indoles investigated. The comparative analysis of the spectra in three types of environment, allows to give the accurate location of the first bands for the two overlapping vibronic systems of these molecules in polar media. Particularly, it is unambiguously shown that the first ¹L_a band and the first ¹L_b band of indole in alcohols are superposed at 288 nm. These results offer reliable new bases for the study of the emission properties of indole and its derivatives.