12-Hydroxy-1-azaperylene—Limiting Case of the ESIPT System: Enol–Keto Tautomerization in S₀ and S₁ States

Abstract

Absorption, fluorescence, and fluorescence excitation spectra of 12-hydroxy-1-azaperylene (HAP) and 1-azaperylene were studied in n-alkane matrices at 5 K. Two stable tautomers of HAP, each of them in n-nonane embedded in two sites, were identified and attributed to the enol and keto forms. Theoretical calculations of the energy and vibrational structure of the spectra suggest that tautomer A, with the (0, 0) transition energy at 18,980 ± 10 cm(-1) (and 19,060 ± 10 cm(-1) in the high energy site), should be identified as the keto form, whereas tautomer B, with the (0, 0) energy at 19,200 ± 20 cm(-1) (19,290 ± 20 cm(-1)), as the enol form. Observation of absorption and fluorescence of both tautomeric forms and lack of large Stokes shift of fluorescence of the keto form classify HAP as the limiting case of the excited-state intramolecular proton transfer system.

Deuterium Isotope Effects on 13C-NMR Chemical Shifts of 10-Hydroxybenzo[h]quinolines

“…HBQs seems a very good group to study some of the abovementioned phenomena and also to establish whether these compounds are tautomeric or not, considering that 12-hydroxy-1-azaperylene, a close analogue, has been found to be tautomeric [19,20,21]. …”

Excited State Intramolecular Proton Transfer in π-Expanded Phenazine-Derived Phenols

“…Excited state inter- and intramolecular proton transfer (ESIPT) − has emerged as an interesting phenomenon that can be utilized in the design of fluorescent sensors. − Compounds displaying ESIPT include benzoxazoles, − flavones, − imidazoles, − imidazo[1,2- a ]pyridines, − and anthraquinones. − The photophysical characteristics of ESIPT-capable compounds make them excellent candidates for applications in such diverse areas as laser dyes, , fluorescence recording, , ultraviolet stabilizers, probes for solvation dynamics, probes for biological environments, and recently, organic light emitting devices. , Although 10-hydroxybenzo[ h ]quinoline (HBQ) represents one of the fundamental heterocyclic systems, in which ESIPT occurs, it was only in 1992 when the fundamental studies of Martinez, Chou, and colleagues identified ESIPT as the process responsible for the strongly bathochromically shifted fluorescence of HBQ. , Detailed photophysical and theoretical studies of HBQ showed very fast and solvent-independent ESIPT, − and recently more elaborated derivatives were also investigated. − …”

Synthesis, crystal structure and DFT studies of a dual fluorescent ketamine: Structural changes in the ground and excited states

“…In the excited state the proton may be transferred from amine group (NH) to keto group (C=O) through ESIPT process leads to the existence of both KHB and EHB forms [18][19][20][21][22][23]33]. In dual emission, the low intensity peak at 410 nm arises from the normal ketamine form and the red shifted high intensity peak at 435 nm corresponds to the stable tautomeric enolimine form.…”

“…This hypothesis leads to the concept of twisted intramolecular charge transfer (TICT) process. A number of reports have shown that the degree of steric hindrance plays an important role in dual emission arises from twisted intramolecular charge transfer (TICT) or excited state intramolecular proton transfer (ESIPT) process [18][19][20][21][22][23].…”