The
search for new prominent chemosensors is significantly
related
to the rationalization of possible multiple pathways of excited-state
deactivation. We have prepared and studied compound α-(2-hydroxyphenyl)-N-phenylnitrone (Nit–OH), observing that Nit–OH
is stable in acetonitrile solution under UV–vis light. The
experimentally observed 540 nm fluorescence for Nit–OH was
shown to be related to excitation at 360 nm from the highest occupied
molecular orbital to the lowest unoccupied molecular orbital (HOMO–LUMO
transition). Potential energy curves (PECs) for the S1 state
of Nit–OH did show that there are structures associated with
excited-state intramolecular proton transfer (ESIPT), and the existence
of an intramolecular H-bonding was confirmed using X-ray powder diffraction
(XRD). Twisted intramolecular charge transfer (TICT) took place following
ESIPT, and a nonradiative deactivation at the S1/S0 conical intersection occurred; aggregation-induced emission
was observed at 540 nm associated with the formation of a stacked
dimer. Anti-Kasha emission from the S2 was proposed based
on the dependence of the fluorescence excitation wavelength on Nit–OH
concentration. From the calculation of the PEC for the S2 state, we obtained radiative transitions at 379 and 432 nm, similar
to the obtained experimental values of 383 and 453 nm. We proposed
a Jablonski-like diagram that depicts all experimental and theoretical
electronic transitions for Nit–OH, summarizing the unique intricate
photophysical behavior of this nitrone derivative.
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