Comparative study of stimulated proton-transfer luminescence of three chromones

Abstract

References 6 and 15.Reference 23. "This work.laser-induced fluorescence was very relaxed and the vibrational bands were not clear.No vibrational information_was seen in the resolved fluorescencespectrum. Excitation of B-X or C-X bands produced strong Á-X emission, probably through collisions and nonradiative decay processes.This type of strong relaxation to lowest excited state has been seen for metal monoalkylamides.23An attempt was made to record the laser excitation spectra by using the monochromator as a band-pass filter to detect the vibronic bands.These experiments gave identical spectra to those which were recorded with the red-pass filters.The M-S stretching frequencies for SrSH and CaSH are given in Table V.The frequencies in all four electronic states are almost the same.Table VI compares the ground-state vibrational frequencies of M-SH with M-OH and M-NH2.The M-S stretching frequencies are less than the corresponding M-0 and M-N (even when the heavier S mass is taken into account), indicating that the force constants are smaller in metal hydro- sulfides.This suggests that dissociation energies are smaller than the corresponding M-OR and M-NHR dissociation energies. ConclusionThe calcium and strontium thiolates were produced in the gas phase by the reaction of the metal vapor with the appropriate thiol.The laser excitation spectra of three electronic transitions C2A'-X2A', B2A"-X2A', and A2A'-X2A' were recorded.By implication, the M-S-C angle in the thiolate derivatives is also not 180°.The observation of a bent CaSH is in contrast to a linear CaOH and suggests considerable covalent character in the Ca-SH bond.The experimental results are in excellent agreement with the theoretical calculations of Ortiz.19These calculations were very helpful in our interpretation of the electronic structure of the alkaline earth thiolates.The ab initio electron propagator calculations seem to have captured the simple one-electron character of the observed electronic transitions.