Computational Insights into Excited State Intramolecular Double Proton Transfer Behavior Associated with Atomic Electronegativity for Bis(2′-benzothiazolyl)hydroquinone

Abstract

Inspired by the distinguished regulated photochemical and photophysical properties of 2-(2′-hydroxyphenyl)benzazole derivatives, in this work, the novel bis(2′-benzothiazolyl)hydroquinone (BBTHQ) fluorophore is explored, looking at its photo-induced behaviors associated with different substituted atomic electronegativities, i.e., BBTHQ-SO, BBTHQ-SS and BBTHQ-Se compounds. From the structural changes, infrared (IR) vibrational variations and simulated core-valence bifurcation (CVB) indexes for the dual hydrogen bonds for the three BBTHQ derivatives, we see that low atomic electronegativity could be conducive to enhancing hydrogen bonding effects in the S1 state. Particularly, the O4-H5⋯N6 of BBTHQ-SO and the O1-H2⋯N3 of BBTHQ-SSe could be strengthened to be more intensive in the S1 state, respectively. Looking into the charge recombination induced by photoexcitation, we confirm a favorable ESDPT trend deriving from the charge reorganization of the dual hydrogen bonding regions. By constructing the potential energy surfaces (PESs) along with the ESDPT paths for the BBTHQ-SO, BBTHQ-SS and BBTHQ-Se compounds, we not only unveil stepwise ESDPT behaviors, but also present an atomic electronegativity-regulated ESDPT mechanism.

Dual-Channel Imine-Amine Photoisomerization in a Benzoimidazole and Benzothiazole Coupled System: Photophysics and Applications

“…The molecule HBT , when excited at 350 nm, shows a large Stokes shifted emission band at ∼520 nm. The band at ∼520 nm was ascribed to the ESIPT from the phenolic –OH to the thiazole moiety. − Similarly, the molecule BIB , when excited at 350 nm, shows an emission band at 465 nm due to ESIPT from phenolic –OH to the imidazole moiety. − The local emission band was observed at 390 and 380 nm for HBT and BIB , respectively − (Figure E,F). Thus, from the spectral comparison of BIBTB with the two control compounds HBT and BIB , we assigned the band at 555 nm to the ESIPT from the phenolic –OH to the thiazole moiety and the band at 500 nm to the ESIPT from the phenolic –OH to the imidazole moiety.…”

“…A red sided absorption band at ∼460 nm also appears when base triethylamine is added to the ACN solution of BIBTB (Figure 3B). 25,29,32 Hence, this absorption band was allocated to the anionic form of BIBTB. The higher acidity of the phenolic −OH proton of BIBTB due to the presence of electron-withdrawing benzothiazole and benzoimidazole moieties facilitates the formation of an anion in basic solvents like MeOH and DMSO with a high dielectric constant.…”

“…25−28 Ground state structural calculation and potential energy curve (PEC) along the PT coordinate in the gas phase and in different solvents have been performed at Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TDDFT) level to correlate with the experimental findings. 29,30 The ultrafast ESIPT process in the imidazole and thiazole system (∼200−300 ps) 26,31 is found to be slowed down in the substituted thiazole 2-(benzo[d]thiazol-2-yl)-4chlorophenol (BTCP) 32 and 3-(benzo[d]-thiazol-2-yl)-2-hydroxy-5-methoxybenzaldehyde (BTHMB). 24 Switching of intramolecular H-bonding was reported in 2-(1,3-benzothiazol-2-yl)-4-methoxy-6-(1,4,5-triphenyl-1H-imidazol-2-yl)phenol (BTImP) by addition of acids/bases.…”

“…The competitive photoinduced PT behavior of the BIBTB molecule has been explored by steady state absorption and emission and time-resolved emission studies. The photophysical properties of BIBTB have been compared with those of the already reported parent molecules thiazole and imidazole and with two controlled synthetic compounds BIB and HBT . − Ground state structural calculation and potential energy curve (PEC) along the PT coordinate in the gas phase and in different solvents have been performed at Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TDDFT) level to correlate with the experimental findings. , The ultrafast ESIPT process in the imidazole and thiazole system (∼200–300 ps) , is found to be slowed down in the substituted thiazole 2-(benzo­[ d ]­thiazol-2-yl)-4-chlorophenol (BTCP) and 3-(benzo­[ d ]-thiazol-2-yl)-2-hydroxy-5-methoxybenzaldehyde (BTHMB) . Switching of intramolecular H-bonding was reported in 2-(1,3-benzothiazol-2-yl)-4-methoxy-6-(1,4,5-triphenyl-1 H -imidazol-2-yl)­phenol (BTImP) by addition of acids/bases .…”

Regulated stepwise ESDPT mechanism associated with chalcogen substitutions in BDIBD derivatives

“…The ESIPT mechanism, which is a fundamental process in our daily lives and the natural world, has been extensively studied, both theoretically and experimentally, since its discovery. 6–11 The ESIPT reaction is known for its exceptional speed, and the remarkable Stokes shift resulting from the formation of tautomers in excited states. 12–16…”