Donor-Functionalized Polydentate Pyrylium Salts and Phosphinines: Synthesis, Structural Characterization, and Photophysical Properties

A series of donor-functionalized pyrylium salts have been prepared by classical condensation reactions which were further converted into the corresponding thienyl- and pyridyl-substituted polydentate λ3-phosphinines by reaction with P(SiMe3)3. Further chemical modification of these phosphorus heterocycles with Hg(OAc)2 in the presence of methanol resulted in the formation of λ5-phosphinines. The photophysical properties of a selected series of thienyl- and pyridyl-functionalized pyrylium salts, λ3- and λ5-phosphinines, were investigated and the results compared and supported by theoretical calculations on the DFT level. Significant fluorescence was observed for the pyrylium salts and λ5-phosphinines. In contrast, the heteroaromatic substituted λ3-phosphinines show very little emission which is consistent with the low oscillator strength predicted by DFT calculations for this π ->π * transition. Furthermore, all three classes of compounds show readily observable phosphorescence in solution, which was determined by time-gated detection at low temperature.