A highly efficient solution and solid state ESIPT fluorophore and its OLEDs application

We present herein the synthesis and the photophysics of 2,2’-bipyridine-3,3’-diol-5,5’-dicarboxylic acid ethyl ester (BP(OH)$_2$DCEt$_2$), an excited state intramolecular proton tranfer (ESIPT)-based fluorophore featuring two identical intramolecular hydrogen bonds. BP(OH)$_2$DCEt$_2$ emits efficiently not only in solution, including protic solvents ($\lambda _{em}$ = 521 nm, $\Phi$$_f$ = 40 to 75%), but also in crystalline state ($\lambda _{em}$ = 530 nm, $\Phi$$_f$ = 51%). In addition, its saponified form (Na2BP(OH)2DC) is highly fluorescent in water ($\lambda _{em}$ = 490 nm, $\Phi$$_f$ = 51%). Finally, the good electroluminescence performance of BP(OH)$_2$DCEt$_2$ is also demonstrated in an OLED device.