Excited‐State Intramolecular Proton Transfer in 2‐(2′‐Hydroxyphenyl)benzoxazole Derivatives

Proton Transfer in Hydrogen-Bonded Network of Phenol Molecules: Intracluster Formation of Water

“…However, this process may be facilitated by the H + ••• PhO − ion-pair formation from one phenol. Although phenol is not a strong acid in the ground state, its acidity increases in the excited states, 33 and thus the proposed pathway may be feasible after the electron ionization, when a substantial amount of excitation energy is likely to be deposited in the cluster ion. Analogous pathways can be drawn for larger phenol cluster ions for the formation of hydrated [ (PhOH) 34 This observation suggests that the proton-transfer process and the subsequent neutral diphenyl ether evaporation from the ionized cluster start to proceed efficiently from the threshold size of the neutral precursor cluster (PhOH) t , t ≈ 4 to 5.…”

Electronic and photophysical properties of 2-(2′-hydroxyphenyl)benzoxazole and its derivatives enhancing in the excited-state intramolecular proton transfer processes: A TD-DFT study on substitution effect

“…Thus, its derivatives [14,25,31,[36][37][38] have also been increasingly investigated both in experiment and theoretical studies. The photophysical behaviors driven by ESIPT of HBO and its derivatives depend not only on solvents but also on their nature and position of various substituents on the phenol fragment as a substituent can influence the hydrogen bonding strength and consequence PT capability [8]. Recently, Ohshima et al [31] reported a comprehensive comparison of electron donating substituents of methoxy (-OCH 3 ) in 3′-, 4′-and 5′-positions of the phenol moiety.…”

“…Due to its intrinsic photophysical property showing a large Stokes shift driven by the excited state intramolecular proton transfer (ESIPT), 2-(2′-hydroxyphenyl)benzoxazole (HBO, shown in Scheme 1) comprising the hydroxyl group (O-H acting as a proton donor) and the benzoxazole group (a nitrogen atom acting as a proton acceptor) has become an interesting compound [1][2][3][4][5][6][7][8][9][10]. Typically, molecules exhibiting ESIPT thermodynamically favor enol form (S 0 enol) in the ground state (S 0 ), which is stabilized by the intramolecular hydrogen bonding, however, upon photoexcitation a fast proton transfer (PT) reaction from the excited enol (S 1 enol) triggers to give the excited keto tautomer (S 1 keto) in subpicosecond time scale [1].…”

Synthesis of New ESIPT-Fluorescein: Photophysics of pH Sensitivity and Fluorescence

“…A variety of molecules have intramolecular hydrogen bonds (H-bonds) that may be photo-induced to undergo proton transfer. ESIPT can be observed in a variety of such molecules that contain both hydrogen donor and acceptor in close proximity. − An intramolecular hydrogen bond generally formed in the ground state will migrate to the neighboring proton acceptor leading to a phototautomer. − In the general family of 2-(2′-hydroxyphenyl) benzimidazole, benzoxazole, benzthiazole, and benztriazole, − the ESIPT phototautomer gives rise to an emission with large Stokes shift. The high intensity of fluorescence emission and large Stokes shift due to intramolecular proton transfer phenomena − allow these molecules to have many interesting applications.…”