Synthesis, experimental and theoretical photophysical study of proton transfer based oxazoline fluorophores. Potential tailor made optical sensors for enantiomeric detection in solution

Abstract

A series of oxazoline based compounds was obtained via amidation formation from salicylic acid derivatives and benzyl-protected l-threonine with good yields (50–90%). These compounds present absorption in the UV region (∼300 nm) and fluorescence emission spectra show large Stokes shift emission (∼10000 cm−1) in the blue-green region attributed to the ESIPT process. TD-DFT calculations were carried out to investigate the process of proton transfer of the structure of both tautomers (keto and enol) and corroborating the UV region absorption and large Stokes shift. The oxazolines derivatives were investigated as optical sensor for enantiomeric identification in solution. Preliminary results indicate sensing for arabinose and tartaric acid, but not specificity. However, to the pair R-(−)-Mandelic and S-(+)-Mandelic acid, the oxazoline 4c showed a enantiomeric selectivity identification, allowing to envisage these compounds as potential photoactive building blocks to propose innovative optical sensors in solution.