A density functional theory‐time‐dependent density functional theory investigation of photo‐induced hydrogen bond and proton transfer for 2‐(3,5‐dichloro‐2,6‐dihydroxy‐phenyl)‐benzoxazole‐6‐carboxylicacid

Abstract

Given the paramount importance of excited-state relaxation in the photochemical process, excited-state hydrogen bonding interactions and excited-state intramolecular proton transfer (ESIPT) are always hot topics. In this work, we theoretically explore the excited-state dynamical behaviors for a novel 2-(3,5-dichloro-2,6-dihydroxy-phenyl)-benzoxazole-6-carboxylicacid (DDPBC) system. As two intramolecular hydrogen bonds (O1 H2Á Á ÁN3 and O4 H5Á Á ÁO6) exist in the DDPBC structure, we first check if the double proton transfer form cannot be formed in the S1 state. Then, we explore the changes of geometrical parameters involved in hydrogen bonds, based on which we confirm that the dual intramolecular hydrogen bonds are strengthened on photo-excitation. The O1 H2Á Á ÁN3 hydrogen bond particularly plays a more important role in excited state. When it comes to the photo-induced excitation, we find charge transfer and electronic density redistribution around O1 H2 and N3 atom moieties. We verify the ESIPT tendency arising from the O1 H2Á Á ÁN3 hydrogen bond. In the analysis of the potential energy curves, along with O1 H2Á Á ÁN3 and O4 H5Á Á ÁO6, we demonstrate that the ESIPT reaction should occur along with O1 H2Á Á ÁN3 rather than O4 H5Á Á ÁO6. This work not only clarifies the specific ESIPT mechanism for DDPBC system but also paves the way for further novel applications based on DDPBC structure in the future. K E Y W O R D Sexcited-state intramolecular proton transfer, frontier molecular orbitals, intramolecular hydrogen bond, potential energy curves

Revelation of ESIPT mechanism for the novel fluorescent system HNIBT in toluene and methanol solvents: A TDDFT study

“…Combining with the enlarged bond angle δ(O1 H2ÁÁÁN3) from 147.65 to 147.98 , we have the reasons to deem that the intramolecular hydrogen bond O1 H2ÁÁÁN3 of HNIBT-enol should be strengthened in S 1 state. [12,[53][54][55][56][57][58][59][60][61] In a similar manner, it can be found O1 H2 distance of HNIBT-MeOH-enol complex is increased in S 1 , whereas H2ÁÁÁN3 length of HNIBT-MeOH-enol complex is shortened with the enlarged bond angle δ(O1 H2ÁÁÁN3). Therefore, we can say the intramolecular hydrogen bond O1 H2ÁÁÁN3 of the HNIBT-MeOH-enol complex is also enhanced.…”

“…Therefore, we can say the intramolecular hydrogen bond O1 H2ÁÁÁN3 of the HNIBT-MeOH-enol complex is also enhanced. [12,[53][54][55][56][57][58][59][60][61] In view of the intermolecular hydrogen bonding interaction of NIBT-MeOH-enol complex, it is worth mentioning, the O1ÁÁÁH4 is elongated from S 0state 1.98657 Å to S 1 -state 2.03398 Å. Meanwhile, the H4 O5 distance shortens from 0.96809 to 0.96724 with the decrescent bond angle δ(O1ÁÁÁH4 O5) (i.e., from S0-state 175.84 to S1-state 172.71 ).…”

“…As mentioned in previous work, IR analyses should be an efficient way for exploring excitedstate hydrogen bonding dynamics. [12,[53][54][55][56][57][58][59][60][61] We display the simulated IR results about the hydroxyl O1 H2 stretching vibrations of both HNIBT-enol and HNIBT-MeOH-enol in Figure 3. It is obvious that the IR value of hydroxyl O1 H2 stretching vibrational mode of HNIBT-enol changes from S 0state 3,125 cm −1 to S 1 -state 2,984 cm −1 .…”

“…That is to say, the distinct red-shift phenomena of hydroxyl stretching vibration should be attributed to the enhanced excited-state intramolecular hydrogen bond O1 H2ÁÁÁN3 for both HNIBT-enol and HNIBT-MeOH-enol. [12,[53][54][55][56][57][58][59][60][61]…”