Trifluoroacetyl-Substituted D-π-A Fluorophores: Design Strategies for Strong Solvatochromism and Giga Stokes Shifts.

Solvatochromic fluorophores, widely employed in various analytical applications such as environmentally responsive dyes, typically feature a donor-π-acceptor (D-π-A) structure. Most recently, Klymchenko and we independently designed D-π-A fluorophores with a strong acceptor, trifluoroacetyl group, to achieve strong fluorescent solvatochromism and reported its application to membrane analysis (Klymchenko et al. Anal. Chem. 2024, 96, 13242) and molecular thermometer (Konishi et al. J. Am. Chem. Soc. 2025, 147, 9953), respectively. However, these reports have only considered a few π-electron donors including dialkylamines. There is not enough scope for solvatochromic fluorophores that take advantage of the properties of the trifluoroacetyl group. In this study, we systematically investigated the fluorescent properties of the π-conjugated aromatic skeleton of D-π-A with trifluoroacetyl groups. The relationship between dye structure and properties such as absorption, fluorescence, and quantum yield were clarified, and a molecular design strategy for fluorophores that exhibit the desired properties was established. Moreover, fluorescence quenching can occur depending on solvent selection or molecular structure. Moreover, this study provides insightful analysis of trifluoroacetyl-based fluorophores design strategy, emphasizing their prospective as strong but underused acceptor units for next fluorophore development.