Exploring the excited state behavior for 2-(phenyl)imidazo[4,5-c]pyridine in methanol solvent

Abstract

In this present work, we theoretically investigate the excited state mechanism for the 2-(phenyl)imidazo[4,5-c]pyridine (PIP-C) molecule combined with methanol (MeOH) solvent molecules. Three MeOH molecules should be connected with PIP-C forming stable PIP-C-MeOH complex in the S0 state. Upon the photo-excitation, the hydrogen bonded wires are strengthened in the S1 state. Particularly the deprotonation process of PIP-C facilitates the excited state intermolecular proton transfer (ESIPT) process. In our work, we do verify that the ESIPT reaction should occur due to the low potential energy barrier 8.785 kcal/mol in the S1 state. While the intersection of potential energy curves of S0 and S1 states result in the nonradiation transition from S1 to S0 state, which successfully explain why the emission peak of the proton-transfer PIP-C-MeOH-PT form could not be reported in previous experiment. As a whole, this work not only put forward a new excited state mechanism for PIP-C system, but also compensates for the defects about mechanism in previous experiment.

A theoretical exploration and regulating about the excited state process for 2‐(4‐(diphenylamino)phenyl)‐3‐hydroxy‐4H‐chromen‐4‐one system

“…Since the theoretical IR vibrational spectra could also reflect the changes about excited‐state hydrogen bonding dynamics, herein, we also perform the simulations about the IR vibrational spectra at the stretching vibrational bond O1―H2. The corresponding results have been shown in Figure .…”

“…It means that the proton H2 shows the tendency of departure O1 atom and getting close to O3 atom in the S 1 state. That is to say, the intramolecular hydrogen bond O1―H2···O3 should be strengthened upon the photo‐excitation process . Moreover, in view of the bond angle δ (O1―H2―O3) also increases from ground‐state 118.9° to first excited‐state 123.1°, which reveals the strengthening tendency of hydrogen bond O1―H2···O3.…”

“…That is to say, when the solvent polarity increases, the ESPT rate can decrease more or less. While it is undeniable that spectroscopic techniques, such as steady‐state absorption and emission spectra, and time‐resolved fluorescence spectroscopy, could just show the indirect information about the photochemical and photo‐physical properties . In addition, even though Chou et al executed some calculations, unfortunately the theoretical part does not consider the solvent effect .…”

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

“…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] .…”