Adiabatic deprotonation as an important competing pathway to ESIPT in photoacidic 2-phenylphenols

Abstract

ESIPT vs. ESPT: an adequate choice of the substitution pattern can take ESIPT to C-atom to another level.

Light-Driven Switching between Intramolecular Proton-Transfer and Charge-Transfer States

“…Similarly, the 550 nm emission is also blue-shifted compared to the TICT emission in a more polar protic solvent, methanol. This is consistent with the fact that with an increase in polarity the tautomer band undergoes a blue shift and the TICT band undergoes a red shift. − ,,,− The blue shift and the red shift indicate the increase and decrease in the energy gap between the ground and the excited state. This means that the excited state of the tautomer is less stabilized than its ground state in the polar environment, and it is just the opposite for the TICT state.…”

“…It is also an important photoprocess and has wide applications in various fields including photoswitches. − Highly Stokes-shifted tautomer emission is an additional advantage of ESIPT over isomerization. TICT depends on the strength of the electron-donor and -acceptor groups present in the fluorophore. − ESIPT depends on the acidity and basicity of the groups those are connected by the intramolecular hydrogen bond. − Hence, the strength of the charge transfer and intramolecular hydrogen bond determines the emission properties of the fluorophores. − It is reported that in 4-(diethylamino)-2-hydroxybenzaldehyde and 2-(4′-diethylamino-2′-hydroxyphenyl)­benz-imidazole, the ESIPT process suppresses the charge-transfer process. , However, in the cases of 4-amino-2-hydroxybenzoicacid and 4-(dimethylamino)-2-hydroxybenzoicacid, the proton-transfer process accelerates the charge-transfer process. , In 5-diethylamino-2-[(4-diethylaminobenzylidene)­hydrazonomethyl]­phenol and N , N ′-bis­(4- N , N -diethylaminosalisalidene)­hydrazine Schiff bases, Guchhait et al demonstrated that the proton-transfer process assists in the charge-transfer process . 4-(Dimethylamino)-2-hydroxybenzoate has been reported to emit triple fluorescence .…”

One-pot synthesis to prepare lignin/photoacid nanohybrids for multifunctional biosensors and photo-triggered singlet oxygen generation

“…PP is a classic example of photoacid so an acidity enhancement was observed upon photo-irradiation, resulting in a large p K a decline in the excited-state () of PP , as expected. 41,42 A solvent molecule and any basic participants can act as the proton acceptors for the photoinduced protons dissociated from the photoacid in the excited state. For some “super” photoacid compounds, reached values slightly greater than zero or even attained negative values.…”

“…This result is consistent with the previous studies on the occurrence of the ESPT process in an organic/ aqueous system in 2-phenylphenol and its derivates. [39][40][41][42] The fluorescent emission of unmodified AL has also been investigated to determine the fluorescence origin in the visible region. At F w = 0.95, AL shows very low emission intensity compared to AL-Por-PP-1 (Fig.…”

“…The nanohybrids were composed of the precursors which were derived from the lignocellulosic biomass refinery industries. Alkali lignin (AL) is a common lignin product from the pulp and paper industries; 4,34,35 2-phenylphenol (PP) is a 5-5′ linkage product [36][37][38] from lignin fractionation and a well explored photoacid [39][40][41][42] ; while 5,10,15,20-tetrakis(4-aminophenyl)-porphyrin (Por) is a photosensitizer inspired by the sophisticated structure in the plant photosynthetic system for generating the energetic triplet state under visible wavelength irradiation. 43 Instead of using the energy demanding and high temperature synthesis methods like hydrothermal, reflux or pyrolysis, the precursors of the AL-Por-PP nanohybrid were linked up rationally with the retrosynthesis concept in a one-pot azo coupling reaction at low temperature.…”