Exploration and elaboration of photo-induced proton transfer dynamical mechanism for novel 2-[1,3]dithian-2-yl-6-(7aH-indol-2-yl)-phenol sensor*

Abstract

In this work, we theoretically probe into the photo-induced hydrogen bonding effects between S0 state and S1 state as well as the excited state intramolecular proton transfer (ESIPT) behavior for a novel 2-[1,3]dithian-2-yl-6-(7 aH-indol-2-yl)-phenol (DIP) probe system. We first study the ground-state hydrogen bonding O–H⋯N behavior for DIP. Then we analyze the primary geometrical parameters (i.e., bond length, bond angle, and infrared (IR) stretching vibrational mode) involved in hydrogen bond, and confirm that the O–H⋯N of DIP should be strengthened in the first excited state. It is the significant prerequisite for ESIPT reaction. Combining the frontier molecular orbitals (MOs) with vertical excitation analyses, the intramolecular charge transfer (ICT) phenomenon can be found for the DIP system, which reveals that the charge redistribution facilitates ESIPT behavior. By constructing potential energy curves for DIP along the ESIPT reactional orientation, we obtain quite a small energy barrier (3.33 kcal/mol) and affirmed that the DIP molecule undergoes ultrafast ESIPT process once it is excited to the S1 state and quickly transfers its proton, forming DIP-keto tautomer. That is why no fluorescence of DIP can be observed in experiment, which further reveals the ultrafast ESIPT mechanism proposed in this work.

Theoretical Insights into Excited‐State Stepwise Double Proton Transfer Associated with Solvent Polarity for 2‐bis(benzothia‐zolyl)naphthalene‐Diol Compound

“…[7][8][9][10] It cannot be denied ESIPT molecules with such tunable photophysical properties have been extensively reported and are widely used in various fields. [11][12][13][14][15] As is well known, ESIPT reaction along with single intramolecular hydrogen bond has been studied for nearly half a century, which is basically clear. [16] However, the excited state dynamics of organic molecular systems containing two or more intramolecular hydrogen bonds is still in the initial stage.…”

Insights into photo‐induced excited state intramolecular proton transfer behavior for the novel 2‐([1, 1′‐biphenyl]‐4‐yl)‐3‐hydroxy‐4H‐chromen‐4‐one system: Effects of solvent polarity

“…Fluorescent sensors are always known as conjugated organic molecules that could emit characteristic fluorescence in UV/Vis region. [19][20][21][22][23][24][25] Because the fluorescence wavelength and emission intensity of the fluorescence probes are obviously affected by the interaction with analyte, the fluorescence chemosensors could sensitively detect environmental molecules and biomolecules, gasses, volatile organic compounds, glucose, cysteine, and even glutathione. [26][27][28][29] Nowadays, a novel B-ring-extended flavonol-based cysteine-ratiometric fluorescent probe Bbph-fla-acr was designed and developed by Sun and Yu, 30 which could be applied to practical ratiometric sensing and non-ratiometric imaging of cysteine in vitro and in vivo.…”

Theoretical insights into photochemical ESITP process for novel DMP-HBT-py compound*

“…On account of this kind of characteristics, practical applications could be expired such as light emitting diodes, fluorescence sensors, molecular switches, cell imaging, and so forth. [31][32][33][34][35][36][37][38][39][40][41][42][43][44] To be specific, energy gap between Franck-Condon excited state and relaxed excited state furnishes the driving force for transformation of proton. In turn, the slope of these two states resolves relative kinetics.…”

“…As mentioned above, in consideration of the distinction of double fluorescence peaks, the large Stokes shift could be demonstrated. [31][32][33][34][35][36][37][38][39][40][41][42][43][44] In other words, observation of a nearly mirror symmetry between absorption and fluorescence spectra illustrates the nuclear configuration of the molecule and its surrounding medium remains close to that of S 0 state over excited state lifetime, [31][32][33][34][35][36][37][38][39][40][41][42][43][44] while the effects of ESIPT on Franck-Condon factors are enough to destroy this kind of mirror symmetry.…”

“…Even though relevant ESIPT phenomenon of DMP-HBT-py molecule could be inferred in experimental manner, [45] as far as we know, experiments could only reveal the indirect information. [31][32][33][34][35][36][37][38][39][40][41][42][43][44] Given current theoretical investigations could provide direct and detailed photo-induced behaviors and excited state dynamical process, [31][32][33][34][35][36][37][38][39][40][41][42][43][44] in this work, we use DFT and TDDFT methods to explore fundamental aspects about different electronic states and interrelated structures. As displayed in Fig.…”