Theoretical Study of the ESIPT Process for a New Natural Product Quercetin

Abstract

The investigation of excited-state intramolecular proton transfer (ESIPT) has been carried out via the density functional theory (DFT) and the time-dependent density functional theory (TDDFT) method for natural product quercetin in dichloromethane (DCM) solvent. For distinguishing different types of intramolecular interaction, the reduced density gradient (RDG) function also has been used. In this study, we have clearly clarified the viewpoint that two kinds of tautomeric forms (K1, K2)originated from ESIPT processconsist inthe first electronic excited state (S1). The phenomenon of hydrogen bonding interaction strengtheninghas been proved by comparing the changes of infrared (IR) vibrational spectra and bond parameters of the hydrogen bonding groups in the ground state with that in the first excited state. The frontier molecular orbitals (MOs)provided visual electron density redistribution have further verified the hydrogen bond strengthening mechanism. It should be noted that the ESIPT process of the K2 form is easier to occur than that of the K1 form via observing the potential energy profiles. Furthermore, the RDG isosurfaces has indicated that hydrogen bonding interaction of the K2 form is stronger than that of the K1 formin the S1 state, which is also the reason why the ESIPT process of the K2 form is easier to occur.

Proton-Transfer and Photo-Deamination Reactive Mechanisms Studies of Amines Compounds

“…The information of wave function has been calculated and analyzed for compounds 1 and 3 in different electronic states via DFT and TDDFT methods, respectively. Most of contemporary researchers have extensively adopted these theoretical methods to investigate photophysical and photochemical reaction mechanisms of organic molecules in the past [9][10][11][12][13][14][15][16][17][18][19][20][21][22]. The whole computational processes are based on the Gaussian 09 program [23].…”

Insight into the excited-state intramolecular double-proton transfer of the 2,5-bis(benzoxazol-2-yl)thiophene-3,4-diol: one-step or stepwise mechanism?

“…Then, the excited keto tautomer deactivates radiatively and goes through a reverse ESIPT, producing ground-state enol form again. Many previous works demonstrated that hydrogen bond plays a significant role in the ESIPT process [39][40][41][42], and thus, it is significantly important to study the hydrogen bond behavior in excited state and its effect on ESIPT process, which not only sheds light on the nature of ESIPT, but also provides constructive ideas for designing and tuning desired fluorophores.…”

Indirect solvent assisted tautomerism in 4-substituted phthalimide 2-hydroxy-Schiff bases

“…Most aprotic solvents shift the equilibrium toward the keto tautomer by increasing the polarity. The polar protic solvents can form intermolecular hydrogen bonds resulting in a stabilized keto form [19][20][21][22]; (iv) the planarity of 2-hydroxy species is essential to intramolecular hydrogen bonding and proton transfer reactions [23][24][25]; (v) last but not least, is the temperature influences on tautomerization and ESIPT efficiency. Several useful papers provide a very insightful investigation of low temperature spectral behavior [26][27][28][29][30].…”