Interplay of Dual-Proton Transfer Relay to Achieve Full-Color Panel Luminescence in Excited-State Intramolecular Proton Transfer (ESIPT) Fluorophores

A new design was applied for the
facile synthesis of pure organic
photoluminescent molecules with dual excited-state intramolecular
proton transfer (ESIPT) sites. In this novel class of emitters, full-color
panel emission from blue, green, and yellow to red, including white
light, can be achieved in different solvents as modulated by the enol–keto­(1st)–keto­(2nd)
tautomer emissions. A comprehensive transient photophysical study
verifies that keto­(1st) and keto­(2nd) have a precursor (<0.8 ps)–successor
(∼20 ps)-relayed absorbance relationship, and then a fast equilibrium
between the two is established, resulting in dual emissions in the
nanosecond scale (∼1900 ps). Through the research on copper
ions’ selective PL response, the dual-ESIPT mechanism was further
verified; in addition, the study of solid-state PL changes upon the
stimulus of organic vapor manifests the potential application sensitivity
of the molecules as dual-ESIPT sensors. Theoretical results including
reaction potential energy surface analyses manifest the fact that
dual-proton transfer goes along a sequential route with a smaller
energy barrier, firmly supporting the experimental results. An intrinsic
system that undergoes intramolecular double proton relayed transfer
is thus established for the achievement of much broadened optical
responses and full-color display, providing reference for the design
and application of advanced dual-ESIPT optical materials.