Spectroscopic and mechanistic insights into solvent mediated excited-state proton transfer and aggregation-induced emission: introduction of methyl group onto 2-(o-hydroxyphenyl)benzoxazole

Excited-state intramolecular proton transfer (ESIPT) reaction plays an important role in biology, materials, and other related fields. The ESIPT-based compounds has been proved to improve effectively fluorescence quantum yield, red-shifted emission, and wide separation between absorption and emission wavelengths (large Stokes shift, LSS). A solvatochromic benzoxazole-based probe, 2-(2-hydroxy-5-methylphenyl)benzoxazole(HBO-pCH(3)), exhibited a typical dual fluorescence phenomenon via the ESIPT reaction in non-polar and weakly polar solvents. The emission bands of normal* (similar to 370 nm) and tautomer* (similar to 500 nm) forms were identified and assigned, based on fluorescence spectroscopy and quantum chemical theoretical calculations. Solvatochromism confirmed ESIPT reaction inhibition by solvent polarity and intermolecular hydrogen bonding. The intramolecular reversal in combination with time-dependent density functional theoretical calculations revealed an emission-strengthening mechanism of ESIPT, coupled with aggregation-induced emission (AIE) (in mixed water/methanol solvents). Thus, this strategy provides an insight into designing potential ESIPT + AIE fluorescent sensors.

Automated summary

Excited-state intramolecular proton transfer (ESIPT) reaction plays a significant role in biology, materials, and related fields. A solvatochromic benzoxazole-based probe exhibited dual fluorescence phenomenon via the ESIPT reaction, and the inhibition of ESIPT reaction by solvent polarity and intermolecular hydrogen bonding was confirmed. The study provides insights into designing potential ESIPT + AIE fluorescent sensors.