Using 7-hydroxy-1-indanone as a prototype (I), which exhibit S excited-state intramolecular proton transfer (ESIPT), chemical modification has been performed at C(2)-C(3) positions by fusing benzene (molecule II) and naphthalene rings,.(molecule III). I undergoes in ultrafast rate of ESIPT, resulting in a unique, tautomer emission (lambda(max) similar to 530 nm), whereas excited-state equilibrium is established for both II and III, as supported by the dual emission and the associated relaxation dynamics. The forward ESIPT (normal to proton-transfer tautomer species) rates for II and III are deduced to be (30 ps)(-1) and (22 ps)(-1) respectively, while the backward ESIPT rates are (11 ps)(-1) and (48, ps)(-1). The ESIPT equilibrium constants are thus calculated to be 0.37 and 2.2 for II, and III,. respectively;giving a corresponding free energy change of 0.59 and -0.47 kcal/mol between normal and tautomer species. For III, normal and tautomer emissions in solid are maximized at 435 and 580 nm, respectively, achieving a, white light generation with Commission.. Internationale de l'Eclairage (CIE) (0.30, 0.27). An organic light emitting diode based on III is also successfully fabricated with maximum brightness of 665 cd m(-2) at 20 V(885 mA cm(-2)) and the CIE coordinates of (0.26, 0.35). The results provide the proof of concept that the white light generation can be achieved in a single ESIPT system.