A new class of excited-state intramolecular proton transfer (ESIPT) dyes based on a 1, 3-bis (imino) isoindole diol motif has been prepared. These molecules exhibit orange emission (∼ 600 nm) with a large apparent Stokes shift (> 6000 cm− 1) and quantum efficiencies up to 45%. Selective modification of the substitutents can be used to shift the equilibrium between the enol and keto forms of the molecule in both the ground and excited states.
