A theoretical study on excited state proton transfer in 2‐(2′‐dihydroxyphenyl) benzoxazole

Abstract

This research investigates the dynamic excited state process for a novel system 2-(2′-dihydroxyphenyl) benzoxazole (DHBO) for excited state proton transfer (ESPT) process based on density functional theory (DFT) and time-dependent DFT (TDDFT) methods. Because 2 intramolecular hydrogen bonds (O 1 -H 2 ···N 3 and O 4 -H 5 ···O 6 ) in DHBO molecules may trigger proton transfer process in the S 1 state, we focus on these 2 hydrogen bonds. Our results show that only the O 1 -H 2 ···N 3 bond has obvious changes in both bond length and bond angle upon photoexcitation. Charge redistribution also confirms that hydrogen bond wire (O 1 -H 2 ···N 3 ) is the best way to achieve the ESPT process in the S 1 state. Considering the ESPT mechanism, our theoretical potential energy curves of DHBO indicate that only the excited state single-proton transfer process occurs via O 1 -H 2 ···N 3 rather than O 4 -H 5 ···O 6 . We believe that our work not only clarifies the excited state dynamical behavior of DHBO but also promotes the investigations about ESPT reactions in intramolecular or intermolecular hydrogen bonded chemical systems. KEYWORDS excited state proton transfer, frontier molecular orbitals, intramolecular hydrogen bond, potential energy curves FIGURE 5 Our constructed potential energy curves based on increasing A, O 1 -H 2 and B, O 4 -H 5 bond lengths from 0.85 to 2.15 Å with steps of 0.05 Å in both the S 0 and S 1 states, respectively LI ET AL. 5 of 6

Theoretical insights into excited‐state process for the novel 2,3‐bis[(4‐diethylamino‐2‐hydroxybenzylidene)amino]but‐2‐enedinitrile system

“…Given the bond angles, δ (O1H2⋯N3) and δ (O4H5⋯N6) also increased from 149.4° to 151.2° in the S 1 state. In other words, these changes about chemical bond distances and bond angles indicate that the dual hydrogen bonds (O1H2⋯N3 and O4H5⋯N6) of BDABE should be strengthened in the S 1 state . In addition, it is well known that the excited‐state hydrogen bonding interactions could also be revealed by theoretical IR vibrational spectra .…”

Fluoride anion sensing mechanism of 2‐(quinolin‐2‐yl)‐3‐hydroxy‐4H‐chromen‐4‐one chemosensor based on inhibition of excited state intramolecular ultrafast proton transfer

“…The ESIPT process was firstly observed and reported more than half a century ago by Weller and coworkers, [ 15–17 ] and since then, more and more researchers have focused on this kind of reaction due to its optoelectronic applications, such as fluorescence sensing, ultraviolet (UV) filters, and molecular switches. [ 18–30 ] Generally, upon photo‐induced excitation, molecules could be projected onto a potential energy that can make the position of proton unstable. The energy gap between the local excited and relaxed excited states provides the driving force for transferring the proton, and in turn, the slope of the surface connecting these two points decides the relative kinetics.…”

Investigation of the intramolecular hydrogen bonding interactions and excited state proton transfer mechanism for both Br-BTN and CN-BTN systems

“…It is well known that hydrogen bonding is one of the most important weak interactions in the natural world, which plays a signicant role in various branches of natural science and engineering elds. [1][2][3][4][5][6] It is operative in the crystallization of materials, the formation of straightforward properties of associated liquids, and the determination of the three-dimensional structures adopted by biomolecules such as proteins and nucleic bases. Particularly, the hydrogen bond can result in relatively stable supramolecular structures.…”