Orientation hydrogen-bonding effect on vibronic spectra of isoquinoline in water solvent: Franck-Condon simulation and interpretation

Abstract

The excited-state orientation hydrogen-bonding dynamics, and vibronic spectra of isoquinoline (IQ) and its cationic form IQc in water have been investigated at the time-dependent density functional theory quantum chemistry level plus Franck-Condon simulation and interpretation. The excited-state orientation hydrogen bond strengthening has been found in IQ:HO complex due to the charge redistribution upon excitation; this is interpreted by simulated 1:1 mixed absorption spectra of free IQ and IQ:HO complex having best agreement with experimental results. Conversely, the orientation hydrogen bond in IQc:HO complex would be strongly weakening in the S state and this is interpreted by simulated absorption spectra of free IQc having best agreement with experimental results. By performing Franck-Condon simulation, it reveals that several important vibrational normal modes with frequencies about 1250 cm involving the wagging motion of the hydrogen atoms are very sensitive to the formation of the orientation hydrogen bond for the IQ/IQc:HO complex and this is confirmed by damped Franck-Condon simulation with free IQ/IQc in water. However, the emission spectra of the IQ and IQc in water have been found differently. Upon the excitation, the simulated fluorescence of IQ in water is dominated by the IQ:HO complex; thus hydrogen bond between IQ and HO is much easier to form in the S state. While the weakened hydrogen bond in IQc:HO complex is probably cleaved upon the laser pulse because the simulated emission spectrum of the free IQc is in better agreement with the experimental results.

Theoretical Elaboration about Excited State Behaviors and Fluoride Anion Sensor Mechanism for 2-{[2-(2-Hydroxy-Phenyl)-1H-Benzoimidazo-5-yl]-Phenyl-Methylene} Malononitrile

“…Coupling with the changed feature of bond distances, we confirm that the intramolecular hydrogen bond O-H•••N should be strengthening in the S 1 state [43][44][45][46][47][48][49][50]. Moreover, to the best of our knowledge, the simulated infrared (IR) vibrational spectra involved in hydrogen bonding moieties should be also another manner to explore excited state intramolecular hydrogen bonding dynamics [51][52][53][54][55][56][57][58][59][60][61][62][63]. Thus, we also calculated the IR vibrational spectra about the O-H stretching vibration.…”

“…Therefore, we can say that our theoretical level is suitable for HBPMM system in this work. In addition, since the frontier molecular orbitals (MOs) should be a well manner to analyze the photoexcitation process [51][52][53][54][55][56][57][58][59][60][61][62][63], the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) have been shown in Figure 2. Herein, we only show these two orbitals due to the first transition (S 0 → S 1 ) mainly involved in these two orbitals.…”

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

“…Just because of its significance in natural world, hydrogen bond has drawn great attention on the relevant topics 1 – 3 . Particularly, excited state intramolecular and intermolecular hydrogen bond dynamics, elaborating properties involved in hydrogen bond in the excited state, plays important roles in many photo-physical and photochemical processes, such as photo-induced electron transfer (PET), intra- or inter- molecular charge transfer (ICT), fluorescence resonance energy transfer (FRET), and so forth 4 – 15 . As one of the fast and quite complex reactions involved in hydrogen bond, the excited state intra- or inter- molecular proton transfer (ESIPT) is considered to be one of the most fundamental and important processes in chemistry, biology and materials 16 – 22 .…”

“…As far as we know, generally speaking, molecules possessing proton donor (O-H or N-H) or acceptor (carbonyl oxygen or aromatic nitrogen) might undergo the ESIPT process upon electronic excitation 4 – 15 . That is to say, a molecule with a proton donor and an acceptor in close proximity may exist ESIPT reaction, yielding a photo-tautomer of the original molecule.…”

The sensing mechanism of fluoride anion for a novel molecule D2: Desilylation and intramolecular charge transfer

“…In order to further reveal the effect of the fluoride‐triggered Si–O bond cleavage reaction in the fluoride‐sensing mechanism of the D2 chemosensor, we calculated the desilylation process, as shown in Figure . The construction of the potential energy curve of the S 0 state is based on the shortening of the F–Si bond length from 5.00 to 1.40 Å in steps of 0.05 Å, which is a good way to deal with the studies of the fluorescence sensor . It can be seen clearly that the formation of the intermediate (i.e., the complex between D2 and the fluoride anion) is endergonic with ~8.157 kcal/mol in the ground state.…”