Dynamic Excited-State Intramolecular Proton Transfer Mechanisms of Two Novel 3-Hydroxyflavone-Based Chromophores in Two Different Surroundings

Abstract

The dynamic excited-state intramolecular proton transfer (ESIPT) mechanisms of two novel 3-hydroxyflavone-based chromophores (1 and 2) in different surroundings (nonpolar cyclohexane and polar acetonitrile solvents), which are reported in the recent work (Chou et al. J. Phys. Chem. A. 2010, 114, 10412), are explored in terms of the density functional theory (DFT) and time-dependent DFT theoretical methods. The computational absorption and emission spectra for the work rendered here were in reasonable agreement with the relevant experiment. In order to present the molecular-level exposition of the ESIPT reactions for these compounds in two different solvents, we calculated the hydrogen bond (HB) parameters, corresponding infrared vibrational frequencies, frontier molecular orbitals, and maps of electron density difference between the S 0 and S 1 states, and the HB strengthening tendency in S 1 states was verified, giving the probability of ESIPT reactions. In addition, to definitely expose the ESIPT mechanisms of compounds 1 and 2, we built the potential energy curves and potential energy surfaces in the S 0 and S 1 states. Calculated results exhibited that the ESIPT reaction of compound 1 in nonpolar cyclohexane solvent was more susceptible than that in polar acetonitrile solvent. For the asymmetric compound 2, only single-ESIPT processes could occur in both the solvents, and double-ESIPT processes were prohibitive due to high potential energy barriers. Moreover, the single-ESIPT processes [I (6.26 kcal/mol) and II (6.62 kcal/mol)] in cyclohexane were more susceptible than that [I′ (6.91 kcal/mol) and II′ (6.90 kcal/mol)] in acetonitrile. Furthermore, the single-ESIPT process I had a little advantage over the process II in cyclohexane, while the probabilities of processes I′ and II′ were roughly the same in acetonitrile.

Efficient excited‐state intramolecular proton transfer in acridone derivatives—A case study of Paratrimerin C

“…In water, we detect a constant red-shift of 160 cm À1 for ν O11 H from N to N*, while more significant red-shift energy of 200-214 cm À1 is found for benzene, which is equal to lower energy of about 0.45-0.57 kcal/mol. This result agrees with previous studies for various OH-containing molecules, such as 4-dimethylaminoflavonol [84] or 3-hydroxy flavone-based chromophores [34].…”

“…The spectroscopic research of the same groups revealed that the emissions of MFOH are easily modulated in hydrocarbon solvents [28], alcoholic solvents [29], weakly aprotic [30,31], and binary mixture solvents [32]. Recently, many authors employed theoretical tools to study the solvent-dependent ESIPT and reported that non-polar solvent is a supportive medium for the ESIPT mechanism because of no solvent perturbation [33,34]. In addition, Peng et al showed that the ESIPT mechanism is inhibited for 1,2-dihydroxyanthraquinone derivatives by the protic solvent (water/methanol); in that medium, only the enol emission is observed [35].…”

Ultraviolet resistance modification of poly(1,3,4‐oxadiazole) fibers by dihydroxyterephthalic acid

“…It is noteworthy that the fluorescence spectral characteristic of DHPOD fibers with double fluorescence emission has also appeared in many excited-state intramolecular proton transfer (ESIPT) molecules whose molecular structures contain intramolecular hydrogen bonds between heterocycles and phenolic hydroxyl groups. [21][22][23][24][25][26][27][28][29][30][31][32] Thus, as similar as ESIPT molecules documented before, DHPOD macromolecules may undergo an ESIPT reaction as well. As depicted in Figure 4b, upon ultraviolet light excitation, the enol tautomer (S 0 ) transits to its first excited state (S 1 ).…”

Theoretical Insights into the Effect of Different Numbers of Thiophene Groups on Hydrogen Bond Interaction and Excited-State Intramolecular Proton-Transfer Process for Flavonoid Derivatives

“…The excited-state intramolecular proton transfer (ESIPT) was first proposed by Weller, who used this mechanism to successfully explain the absorption spectra and double fluorescence spectra phenomena generated by methyl salicylate molecules. Since then, ESIPT has been extensively studied due to its special photophysical and photochemical properties. − ESIPT refers to the proton-transfer process that occurs in excited-state molecules between the adjacent proton donor and proton acceptor upon photoexcitation. The ESIPT reaction is a four-step photoinduced tautomerism process.…”