Correlation between Excited-State Intramolecular Proton Transfer and Electron Population on Proton Donor/Acceptor in 2-(2′-Hydroxyphenyl)oxazole Derivatives

Abstract

Modulating the excited-state intramolecular proton transfer (ESIPT) reaction to achieve anticipant performance is always fascinating for chemists. However, feasible methods and a definite mechanism for tuning the ESIPT reaction remain insufficient. In this work, we reported the feasibility of continuously modulating the ESIPT dynamics in 2-(2′-hydroxyphenyl)­oxazole (HPO) derivatives with different substitutions on the positions 5 and 5′ of the core HPO through steady-state/transient spectroscopy and theoretical calculations. We found that the main factor affecting the tendency of the ESIPT reaction is the variation of electron population on proton donor and acceptor. An index Δp dif was proposed to evaluate the overall promotion effect on proton transfer caused by the variation of electron population on proton donor and acceptor, which shows high reliability in interpreting the ESIPT tendency. This method, for its capacity to quickly estimate the tendency of ESIPT, shows great potential in ESIPT molecular design with chemical substitution of electron-donating/withdrawing moieties.

Precise Manipulation of Excited-State Intramolecular Proton Transfer via Incorporating Charge Transfer toward High-Performance Film-Based Fluorescence Sensing

“…Different from the sole CT process in the ground state, both ESIPT and excited-state ICT reactions could be involved in the processes upon photoexcitation. Typical Keto tautomer emission that peaked at 520 nm in NaCBO was clearly observed (Figure a), a result of efficient ESIPT. , Moreover, the decreased emission intensity in the polar solvent could be an indication of a dark-state existing in the Keto form. Similar observations were reported by others. − In addition to the efficient ESIPT as observed in NaCBO , the CCl 4 solution of PaCBO depicted an additional emission at much longer wavelength (∼580 nm), suggesting another stabilized excited state (bright state) related to the possible Enol form (Figure b).…”

“…Typical Keto tautomer emission that peaked at 520 nm in NaCBO was clearly observed (Figure 2a), a result of efficient ESIPT. 26,29 Moreover, the decreased emission intensity in the polar solvent could be an indication of a dark-state existing in the Keto form. Similar observations were reported by others.…”

Azaindolizine proton cranes attached to 7-hydroxyquinoline and 3-hydroxypyridine: a comparative theoretical study

“…This smaller HOMO–LUMO gap is a crude, yet useful, way of estimating the conjugation. 123 Actually, it is observed that the HOMO–LUMO gap decreases from E to K , but without different trends between A and B PCU.…”

Excited state proton transfer in the triplet state of 8-hydroxy-5-nitroquinoline: a transient absorption and time-resolved resonance Raman spectroscopic study

“…The experimental apparatus has previously been described in detail. [46][47][48] In brief, a regenerative Ti/sapphire amplifier (Astrella, Coherent) generates an 800 nm laser pulse (1 kHz, 7 mJ, 40 fs) that was split into two beams. One beam was converted into the pump pulses (320 nm) through an optical parametric amplifier (TOPAS-C, Light Conversion), while the other was used by a CaF 2 plate to produce the probe white light (370-760 nm).…”