A TD‐DFT study on the hydrogen bonding of three esculetin complexes in electronically excited states: Strengthening and weakening

Abstract

Time-dependent density functional theory (TD-DFT) method was used to study the excited-state hydrogen bonding of three esculetin complexes formed with aprotic solvents. The geometric structures, molecular orbitals (MOs), electronic spectra and the infrared (IR) spectra of the three doubly hydrogen-bonded complexes formed by esculetin and aprotic solvents dimethylsulfoxide (DMSO), tetrahyrofuran (THF) and acetonitrile (ACN) in both ground state S(0) and the first singlet excited state S(1) were calculated by the combined DFT and TD-DFT methods with the COSMO solvation model. Two intermolecular hydrogen bonds can be formed between esculetin and the aprotic solvent in each hydrogen-bonded complex. Based on the calculated bond lengths of the hydrogen bonds and the groups involved in the formation of the intermolecular hydrogen bonds in different electronic states, it is demonstrated that one of the two hydrogen bonds formed in each hydrogen-bonded complex is strengthened while the other one is weakened upon photoexcitation. Furthermore, it is found that the strength of the intermolecular hydrogen bonds formed in the three complexes becomes weaker as the solvents change from DMSO, via THF, to ACN, which is suggested to be due to the decrease of the hydrogen bond accepting (HBA) ability of the solvents. The spectral shifts of the calculated IR spectra further confirm the strengthening and weakening of the intermolecular hydrogen bonds upon the electronic excitation. The variations of the intermolecular hydrogen bond strengths in both S(0) and S(1) states are proposed to be the main reasons for the gradual spectral shifts in the absorption and fluorescence spectra both theoretically and experimentally.

A DFT/TDDFT investigation of the excited state proton transfer reaction of fisetin chromophore

“…The geometric optimizations of fisetin-enol, fisetin-open and fisetin-enol were performed using DFT in the S 0 state and using TDDFT in the S 1 state. Especially, the TDDFT method has become a very useful tool to theoretically investigate the hydrogen bonding interaction that occurs in the excited-state of hydrogen-bonded systems [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]. In addition, Becke's three-parameter hybrid exchange functional with Lee-Yang-Parr gradient-corrected correlation (B3LYP functional) was selected in both the DFT and TDDFT methods [69][70][71][72].…”

“…Up to now, many different sensing mechanisms, such as intramolecular charge transfer (ICT), photo-induced electron transfer (PET), fluorescence resonance energy transfer (FRET), and excited state proton transfer (ESPT) and so forth [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38], are relevant with hydrogen bonding. Particularly, the excited state interand intra-molecular proton transfer (ESIPT) reactions have been drawing great attention due to their unique photo-physical and photo-chemical properties.…”

Photoinduced excited state intramolecular proton transfer and spectral behaviors of Aloesaponarin 1

“…Being a hot topic in biology and chemistry, intramolecular and intermolecular hydrogen bond interactions of some molecular systems have been extensively studied by both experimental and theoretical methods [12][13][14][15][16][17][18][19][20][21][22][23][24][25]. The ESIPT process through hydrogen bond interaction has been used to interpret the spectral behaviors of molecular system due to its important role in practical application [26][27][28].…”

“…The molecules undergoing ESIPT process can be candidates for molecular systems, such as optical memory, photolabeling, proton-transfer laser and an information storage device at the molecular level [29][30][31][32][33][34][35][36][37][38][39][40]. The ESIPT processes of some molecular systems often occur through intermolecular or intramolecular hydrogen bond, which are central to understanding their spectral behaviors and microscopic structure [12][13][14][15][16][17][18][19][20][21][22][23][24][25].…”

Effects of intermolecular hydrogen bonding on the excited-state proton transfer properties of the cinnamonitrile–methanol complex

“…17 Recently, it has been demonstrated that the time-dependent density functional theory (TD-DFT) method can be used to effectively study the electronic transitions and excited-state properties of hydrogen-bonded complexes. [18][19][20][21][22][23][24][25][26][27][28] Therefore, to investigate the excited-state hydrogen bonding effects on the transfer properties of the hydrogen-bonded 3TPAN-MeOH complex, the geometric structures and electronic transition energies as well as corresponding oscillation strengths of the two low-lying electronically excited states S 1 and S 3 for both the 3TPAN monomer and the hydrogen-bonded 3TPAN-MeOH complex were calculated by DFT and TD-DFT methods, respectively. In addition, the molecular orbitals (MOs) involved in the S 1 and S 3 electronic transitions for both the 3TPAN monomer and the hydrogen-bonded 3TPAN-MeOH complex were also computed.…”