DFT/TDDFT Study on the Sensing Mechanism of a Fluorescent Probe for Hydrogen Sulfide: Excited State Intramolecular Proton Transfer Coupled Twisted Intramolecular Charge Transfer

Abstract

By using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, the sensing mechanism of a fluorescent probe 2-(2-hydroxyphenyl) benzothiazole (HBT) derivative HBTPP-S for hydrogen sulfide has been thoroughly studied. The thiolysis reaction has a moderate reaction barrier of 18.40 kcal mol, which indicates that the hydrogen sulfide sensing process has a favorable response speed. Because of the nonradiative donor-excited photoinduced electron transfer (d-PET, fluorophore as the electron donor) from the excited HBTPP group to the electron-withdrawing 2,4-dinitrophenyl group, as well as the inhibition of the proton transfer (PT) and the excited state intramolecular proton transfer (ESIPT) process by 2,4-dinitrophenyl group, the probe HBTPP-S is essentially nonfluorescent. On the other hand, the added hydrogen sulfide induces the thiolysis of the 2,4-dinitrophenyl ether bond, and then the thiolysis product HBTPP comes into existence. The theoretically simulated potential energy surface demonstrates that without the electron-withdrawing 2,4-dinitrophenyl group, the thiolysis product HBTPP undergoes the excited state intramolecular proton transfer (ESIPT) coupled twisted intramolecular charge transfer (TICT) processes in the first excited state. The absence of the d-PET and the process mentioned above may explain the significant fluorescent turn-on response and large Stokes shift of the thiolysis product HBTPP.

A theoretical investigation about sensing mechanism of fluoride anion for (E)‐2‐(2‐(dimethylamino)ethyl)‐6‐(4‐hydroxystyryl)‐1H‐benzo[de]‐isoquinoline‐1,3 (2H)‐dione

“…In addition, to further reveal the effect of the fluoride‐triggered deprotonation process in the fluoride‐sensing mechanism of NIM chemosensor, we also calculate the corresponding potential energy curves as shown in Figure A. The potential energy curve of S 0 state is based on the shortening of F and H atom of hydroxy from 2.00 to 0.90 Å with fixing the step of 0.05 Å, which has been confirm to be a good manner to deal with the studies of protonated and deprotonated processes . It can be seen clearly that the potential energy curve almost keeps steady from 2.00 to 1.4 Å, while it appears a sharp decrease after closing H–F around 1.40 Å.…”

Theoretical insights into the fluoride anion response mechanism of a fluorescence chemosensor 4‐((tert‐butyldiphenylsilyl)oxy)isophthalaldehyde

“…Because environmental surroundings can affect the fluorescent probes, the emission intensity or wavelength could be affected via the interactions between environmental molecules and the probe molecules. [1][2][3][4][5] As the most electronegative and smallest anion, the fluoride anion is of great interest because it should be the key species involved in dental care, food science, and osteoporosis. [6][7][8] In the past few years, the recognition and detection of fluoride anions have been the top issue due to their dual function.…”

The excited state hydrogen bond and proton transfer mechanism of a novel dye CS‐Azine

“…Meanwhile, the most significant Stokes shift could be observed for keto* form, and this shift can be as large as 8000 to 12 000 cm ‐1 . Just due to this kind of fluorescence properties for ESIPT reaction, this process can facilitate charge redistribution, and based on which lots of applications about ESIPT molecules have been reported, such as laser dyes, LEDs, fluorescence sensors, molecular switches, and so forth …”

“…Just due to this kind of fluorescence properties for ESIPT reaction, this process can facilitate charge redistribution, and based on which lots of applications about ESIPT molecules have been reported, such as laser dyes, LEDs, fluorescence sensors, molecular switches, and so forth. [31][32][33][34][35][36][37][38][39][40][41][42][43] In fact, most of ESIPT processes refer to the single proton transfer, which occurs along with one intramolecular or intermolecular hydrogen bond in the excited state. While, as a matter of fact, most materials and biosystems contain two or multiple hydrogen bonds.…”