Multisensing Emissive Pyrimidine

Graphical Abstract

Versatile: The fluorescence of a pyridine-modified T-mimic responds to acidity, viscosity, and polarity (see picture).

Abstract

Fluorescent nucleoside analogs, commonly used to explore nucleic acid dynamics, recognition and damage, frequently respond to a single environmental parameter. Herein we address the development of chromophores that can simultaneously probe more than one environmental factor while having each associated with a unique spectroscopic signature. We demonstrate that an isomorphic emissive pyridine-modified 2-deoxy-uridine 1, containing multiple sensory elements, responds to changes in acidity, viscosity, and polarity. Protonation of the pyridine moiety (pK_a 4.4) leads to enhanced emission (λ_em=388 nm) and red-shifted absorption spectra (λ_abs=319 nm), suggesting the formation of an intramolecular hydrogen bond with the neighboring pyrimidine carbonyl. This “locked” conformation can also be mimicked by increasing solvent viscosity, resulting in a stark enhancement of emission quantum yield. Finally, increasing solvent polarity substantially impacts the chromophore’s Stokes shift [from 5.8×10³ cm⁻¹ at E_T(30)=36.4 kcal mol⁻¹ to 9.3 ×10³ cm⁻¹ at E_T(30)=63.1 kcal mol⁻¹]. The opposite effect is seen for the impact of solvent polarity of the protonated form. The characteristic photophysical signature induced by each parameter facilitates the exploration of these environmental factors both individually and simultaneously.