Time-Dependent Density Functional Theory Study on Electronically Excited States of Coumarin 102 Chromophore in Aniline Solvent: Reconsideration of the Electronic Excited-State Hydrogen-Bonding Dynamics

Abstract

The time-dependent density functional theory method was performed to investigate the electronically excited states of the hydrogen-bonded complex formed by coumarin 102 (C102) chromophore and the hydrogen-donating aniline solvent. At the same time, the electronic excited-state hydrogen-bonding dynamics for the photoexcited C102 chromophore in solution was also reconsidered. We demonstrated that the intermolecular hydrogen bond CO...H-N between C102 and aniline molecules is significantly strengthened in the electronically excited-state upon photoexcitation, since the calculated hydrogen bond energy increases from 25.96 kJ/mol in the ground state to 37.27 kJ/mol in the electronically excited state. Furthermore, the infrared spectra of the hydrogen-bonded C102-aniline complex in both the ground state and the electronically excited state were also calculated. The hydrogen bond strengthening in the electronically excited-state was confirmed for the first time by monitoring the spectral shift of the stretching vibrational mode of the hydrogen-bonded N-H group in different electronic states. Therefore, we believed that the dispute about the intermolecular hydrogen bond cleavage or strengthening in the electronically excited-state of coumarin 102 chromophore in hydrogen donating solvents has been clarified by our studies.

Solvation and Protonation of Coumarin 102 in Aqueous Media: A Fluorescence Spectroscopic and Theoretical Study

“…Theoretical calculations, however, indicated the initial strengthening of hydrogen bonds in these complexes after the excitation of the dye molecule. [26][27][28][29] Excited state proton transfer of C102 was observed in the acidic aqueous 30 and ethanol 31 solutions of the dye. It was manifested as a stretch of the rising edge of the fluorescence decay curves measured in the emission wavelength range of the protonated species.…”

Cooperative Excited-State Hydrogen Bond Strengthening and Weakening and Concerted Excited-State Proton Transfer and Twisted Intramolecular Charge Transfer of Thiazolidinedione Derivatives in Solution

“…The intermolecular hydrogen bond strengthening mechanism between Coumarin 102 chromophore and solvent upon photoexcitation has been demonstrated for the first time by Han and coworkers [6], which is in contrast to the mechanism of excited-state intermolecular hydrogen bond cleavage proposed by Nibbering and coworkers [7]. Then, as reconsidered and verified by many other groups [8][9][10], Nibbering and coworkers also accepted the excited-state intermolecular hydrogen bond strengthening mechanism in 2012, and with the help of the mechanism, they have clarified the photoinduced electron-transfer dynamics of 9-fluorenone in amine solvents [11]. Interestingly, an investigation of thiocarbonyl chromophores in solutions indicates an electronic excited-state intermolecular hydrogen bond weakening phenomenon [12].…”

Excited-state hydrogen bonding dynamics of methyl isocyanide in methanol solvent: A DFT/TDDFT study

“…Over the past decades, the hydrogen bond has received great attention because of its importance on determining the structural stability of many chemical complexes and biological macro molecules [1][2][3][4][5][6][7][8][9][10][11][12][13]. Intermolecular hydro-cited state [6,11,[27][28][29][30][31][32][33][34][35].…”