Exploring a new class of efficient boranil-like fluorescent benzoxazaborinines engendered from amino acid counterparts: A synthetic and spectral investigation

Abstract

A series of new benzoxazaborinines was prepared from the salicylaldehyde Schiff bases derived from amino acid esters by a simple complexation reaction between the Schiff bases and boron trifluoride with up to 85 % yield. Single crystal X-ray diffraction studies on 4b further threw light on the three-dimensional structure of the compound. The absorption and emission maxima for all the compounds were observed in the range of 330–353 nm and 435–517 nm, respectively. Compounds 4f and 4l with a tryptophan moiety displayed significantly higher Stokes shifts of 187 and 151 nm respectively, compared with the other derivatives which were in the range of 86–94 nm. Most of the compounds displayed significant quantum yields of up to 80.8 %. The band gaps of the compounds were also calculated by DFT calculations and were found to complement the same calculated by the UV–Vis spectra and were in the range of 2.46–3.93 eV. The tryptophan derivatives, 4f and 4l were found to possess the lowest band gap.