Acridine-based fluorophores with improved lightfastness properties

Abstract

9-arylated acridine-based derivatives (AUPAO &AUEA) with high visibility, fluorescence, and excellent lightfastness were synthesized in good yield. The molecules were characterized by 1H NMR, 13C NMR, HRMS and further investigated for photophysical properties. Initially, absorption and emission studies were carried out in wide-ranging polarity solvents to choose a solvent of interest for further investigations. Concentration-dependent studies were carried out in ethanol to determine an optimized concentration to study lightfastness studies. These molecules showed excellent lightfastness properties in solution form when compared to commercially available acridine orange. pH-dependent studies were also carried out to observe the behavior of cationic dyes in a wide range of pH to optimize pH for dyeing. The presence of extended conjugation at the 9th position and additional four methoxy groups resulted in highly fluorescent dyes with excellent quantum yield. The steric interactions, higher twist, and unrestricted rotation of the conjugation pathway between the aromatic ring at the 9th position and the acridine core decreased the transition probability and energy transfer that helped improve the lightfastness. The introduction of a hydroxyl group in AUEA increased the solubility and helped in controlled dispersion while dyeing. Further, they were dyed on modacrylic fabric as high visibility fluorophores, and later the color coordinates, color strengths were measured.