New fluorescent probes based on 3-(2-benzoxazol-5-yl)alanine skeleton—Synthesis and photophysical properties

N-(tert-butoxycarbonyl)-3-(benzoxazol-5-yl)alanine methyl ester derivatives substituted in position 2 by heterocyclic group were synthesized and their photophysical properties in methanol, acetonitrile and methylcyclohexane were studied by means of absorption and fluorescence spectroscopies. The positions of their emission bands depend on the solvent polarity and are shifted to longer wavelengths in more polar solvents as a result of a charge transfer from a substituent to the benzoxazole moiety. High molar absorption coefficient values and fluorescence quantum yields are characteristic for most of the compounds studied making them efficient fluorescent probes. Moreover, the presence of additional heteroatom in the substituent enables those compounds to act as chemosensors for metal ions or protons.