Elaboration and controlling excited state double proton transfer mechanism of 2,5-bis(benzoxazol-2-yl)thiophene-3,4-diol

Abstract

In the present work, we theoretically illuminate the excited state double proton transfer (ESDPT) process about a novel synthesized system 2,5-bis(benzoxazol-2-yl)thiophene-3,4-diol (BBTD). Minor changes of both structure and charge redistribution deriving from photoexcitation result in obviously different excited state dynamical process. Exploration about our constructed S1-state potential energy surface (PES) indicates a stepwise ESDPT mechanism for BBTD. In addition, we present a new mechanism about regulating and controlling stepwise ESDPT process via external electric field.

Theoretical insights into excited-state hydrogen bonding effects and intramolecular proton transfer (ESIPT) mechanism for BTS system

“…It indicates that the net electron densities shift from hydroxyl groups to atoms N3 and N6 upon photoexcitation of BTS from state S 0 to state S 1 . Particularly, the CDD figure reveals more obvious charge redistributions via hydrogen bond O1-H2···N3, which provides the tendency for ESIPT reaction [26][27][28][29][30][31][32][33][34][35] . Therefore, we can infer that hydrogen bond O1-H2···N3 should play a more important role during the ESIPT process of BTS.…”

“…Constructing and analyzing potential energy curves should be an efficient manner to explore the ESIPT mechanism [26][27][28][29][30][31][32][33][34][35] . For BTS system, we could firstly exclude the excited-state double proton transfer process since the BTS-PT3 structure owns the highest energy (seen in Fig.…”

“…By the light of nature, both applied and cognitive attention have been paid to ESIPT phenomenon, which becomes a demanding subject of research [19][20][21][22][23][24][25] .Generally, ESIPT means the transfer of a hydroxyl (or amino) proton to an oxygen (or nitrogen) acceptor via pre-existing hydrogen bonds. Upon photoexcitation, an unstable position of proton is resulted from the projection of the nuclear wave function of molecule on the excited-state potential energy surface (PES) [26][27][28][29][30][31][32][33][34][35] . The driving force for ESIPT is provided by the energy gap between the initial and relaxed excited states.…”

“…Demonstrating by the mirror symmetry between absorption and emission spectra, the nuclear configuration of the target molecule remains close to that of the ground state over the excited-state lifetime. The mirror symmetry should be broken up by the influence of ESIPT on the Franck-Condon factors [26][27][28][29][30][31][32][33][34][35] . The proton-transfer tautomer emits fluorescence at longer wavelength and results in larger Stokes shifts.As far as we know, single ESPT process may not be sufficient to investigate the complex hydrogen bonding behaviors in biological fields, since more and more photo-induced mutations refer to multiple protons [36][37][38][39] .…”

Exploring the possibilities of double proton transfer in hydrazides: A theoretical approach

“…Further, owing to the presence of a long-range correction scheme present in CAM-B3LYP, excited state dynamics can be predicted accurately to a greater extent than B3LYP. [39][40][41][42][43][44] The selfconsistent field (SCF) convergence thresholds pertaining to energy minimizations for both S0 and S1 state optimizations were set to 10 −6 . The effect of solvent on the energy parameters of the system was studied by using selfconsistent reaction field based on polarizable continuum model (PCM) [45] using the integral equation formalism variant (IEFPCM).…”