Improved Solvatochromism and Quantum Yields in Acridine through Polarity-Enhanced π-Conjugation

Fluorophores exhibiting strong solvatochromism are strongly desired for applications in cellular imaging, photodevices, and fluorescence sensing. However, achieving high quantum yields in increasingly polar environments remains a significant challenge due to the complex balance required between a high transition dipole moment and a low emission energy. In this study, we present an acridine derivative of pyrene, Ad-Py, which features a donor-π-acceptor (D-π-A) scaffold. Notably, this fluorophore demonstrated a strong solvatochromic property, exhibiting a red-shift of 113 nm, along with high quantum yields (<i>Φ</i>_f = 83.5-90.6%) from the less polar solvent <i>n</i>-hexane to the highly polar solvent dimethyl sulfoxide (DMSO). The incorporation of the pyrene moiety effectively extended the π-conjugation of Ad-Py in polar solvents and finely tuned the proportion of the charge transfer (CT) state, leading to enhanced quantum yields. Moreover, due to its sensitivity to microenvironmental changes, Ad-Py facilitated the visual measurement of SO₂, achieving a detection limit of <10 ppb.