A theoretical investigation on the excited state intramolecular single or double proton transfer mechanism of a salicyladazine system

Abstract

Given the tremendous potential applications of excited state intramolecular proton transfer (ESIPT) systems, ESIPT molecules have received widespread attention. In this work, based on density functional theory (DFT) and time‐dependent DFT (TDDFT) methods, we theoretically study the excited state dynamical behaviors of salicyladazine (SA) molecules. Our simulated results show that the double intramolecular hydrogen bonds of SA are strengthened in the S1 state via exploring bond distances, bond angles, and infrared (IR) vibrational spectra. Exploring the frontier molecular orbitals (MOs), we confirm that charge redistributions indeed have effects on excited state dynamical behaviors. The increased electronic densities on N atoms and the decreased electronic densities on O atoms imply that charge redistribution may trigger the ESPT process. Analyzing the constructed S0‐state and S1‐state potential energy surfaces (PESs), we confirm that only the excited state single proton transfer reaction can occur although SA possesses two intramolecular hydrogen bonds. In this work, we clarify the specific ESIPT mechanism, which may facilitate developing novel applications based on the SA system in future.

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.…”

“…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]…”

“…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 ).…”