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

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 (lambda abs=377 nm; lambda em=433 nm; epsilon=13,200 M-1 cm-1; phi F=88 %) through C3-aryl and C4-ester substitutions followed by cyclization. Furthermore, by applying the intramolecular charge transfer (ICT) principle, we invented a bright green fluorophore through C3- and C4-diester and C6-aryl substitutions. The ICT fluorophore based on the pyridone structure shows large molar absorptivity (epsilon=20,100 M-1 cm-1), longer emission wavelength (lambda em=539 nm), high emission quantum yield (phi F=74 %), and large Stokes shift (Delta v=5720 cm-1), which are comparable to those of practical fluorescent probes. TOC sentence: A rational design strategy for 2-pyridone-based fluorophores with bright emission at long wavelengths is proposed. An intramolecular charge transfer-based 2-pyridone fluorophore with large molar absorptivity (epsilon=20,100 M-1 cm-1), longer emission wavelength (lambda em=539 nm), high emission quantum yield (phi F=74 %), and large Stokes shift (Delta v=5720 cm-1) is developed by the strategy.+image