Substituent-regulated photophysical properties of 8a-methyl-2,3-diphenylindolizin-1(8aH)-one derivatives and their application in the detection of bilirubin in blood and urine

Abstract

8a-Methyl-2,3-diphenylindolizin-1(8aH)-one derivatives with electronically diverse substituents at the para position of the C-2 and C-3 phenyl rings were synthesized, and their photophysical properties were examined. The electronic effects exerted by the substituents on the C-2 phenyl ring caused a shift in the emission wavelength, whereas the substituents on the C-3 phenyl ring had no impact. One of the derivatives with p-nitrophenyl group as the C-2 substituent exhibited intramolecular charge transfer characteristics. The solvent-polarity-dependent emission properties facilitated its application as a sensor for detecting moisture in nonpolar solvents with a lowest detection limit of 0.009%. These compounds also responded to bilirubin with a turn-off response, allowing its detection in blood and urine at submicromolar levels. Emission quenching in the presence of bilirubin was attributed to the primary inner filter effect.