Design of 2‐Pyridone Fluorophores for Brighter Emissions at Longer Wavelengths

Abstract The recent discovery of blue fluorophores with high quantum yields based on pyridone structures inspired the development of new low‐molecular‐weight fluorophores with bright emissions at tunable wavelengths, which are highly attractive for various applications. In this study, we propose a rational design strategy for 2‐pyridone‐based fluorophores with bright emissions at long wavelengths. With a detailed understanding of the positional substitution effects on each carbon atom of the 2‐pyridone core, we developed a bright blue fluorophore (λ abs =377 nm; λ em =433 nm; ϵ=13,200 M −1 cm −1 ; ϕ F =88 %) through C 3 ‐aryl and C 4 ‐ester substitutions followed by cyclization. Furthermore, by applying the intramolecular charge transfer (ICT) principle, we invented a bright green fluorophore through C 3 ‐ and C 4 ‐diester and C 6 ‐aryl substitutions. The ICT fluorophore based on the pyridone structure shows large molar absorptivity (ϵ=20,100 M −1 cm −1 ), longer emission wavelength (λ em =539 nm), high emission quantum yield (ϕ F =74 %), and large Stokes shift (Δv=5720 cm −1 ), which are comparable to those of practical fluorescent probes.