Rational Design of a Solvatochromic Fluorescent Uracil Analogue with a Dual‐Band Ratiometric Response Based on 3‐Hydroxychromone

Fluorescent nucleoside analogues with strong and informative responses to their local environment are in urgent need for DNA research. In this work, the design, syn- thesis and investigation of a new solvatochromic ratiometric fluorophore compiled from 3-hydroxychromones (3HCs) and uracil fragments are reported. 3HC dyes are a class of multi- parametric, environment-sensitive fluorophores providing a ratiometric response due to the presence of two well-re- solved bands in their emission spectra. The synthesized con- jugate demonstrates not only the preservation but also the improvement of these properties. The absorption and fluo- rescence spectra are shifted to longer wavelengths together with an increase of brightness. Moreover, the two fluores- cence bands are better resolved and provide ratiometric re- sponses across a broader range of solvent polarities. To un- derstand the photophysical properties of this new fluoro- phore, a series of model compounds were synthesized and comparatively investigated. The obtained data indicate that uracil and 3HC fragments of this derivative are coupled into an electronic conjugated system, which on excitation attains strong charge-transfer character. The developed fluorophore is a prospective label for nucleic acids.