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Femtosecond electronic relaxation and real-time vibrational dynamics in 2′-hydroxychalcone

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Abstract

Femtosecond ultrafast electronic relaxation and vibrational dynamics in 2′-hydroxychalcone after deep ultraviolet (DUV) excitation were observed by two types of pump–probe spectroscopy experiments, i.e., DUV-pump pulse and visible-broadband-probe pulse (DUV/Vis) experiments and DUV-pump and DUV-probe (DUV/DUV) pulse experiments. Time-dependent density functional theory (TDDFT) calculations were performed to elucidate relaxation dynamics from the third singlet electronic excited state S3. The DUV/Vis experiments and TDDFT calculations have disclosed the ultrafast dynamics of internal conversion from the initial S3 state (τ1 ≈ 35 fs) to the S1 state via a rapid process through the S3/S2 conical intersection and proton transfer [OH: τ2(H) ≈ 93 and OD: τ2(D) ≈ 164 fs] before deactivation through the S1/S0 conical intersection (τ3 ≈ 690 fs). Thanks to the ultrashort pump and probe pulses, real-time observation of vibrational modes coupled to the electronic excitation was realized providing both amplitudes and phases. Spectrogram analyses were performed based on the real-time spectra obtained by the DUV/Vis experiments, in which instantaneous vibrational frequencies reflecting molecular structural change after the impulsive excitation were visualized. The vibrational frequency of central C[double bond, length as m-dash]C bond stretch decreases from ∼1600 cm−1 to ∼1560 cm−1 in about 200–500 fs and recovers in ∼550 fs. Normal mode analyses along the decay path support the observed variation of the C[double bond, length as m-dash]C stretching frequency. The temporal weakening of the central C[double bond, length as m-dash]C bond is connected with the angle of the two aromatic rings which flip back to the initial conformation.

Graphical abstract: Femtosecond electronic relaxation and real-time vibrational dynamics in 2′-hydroxychalcone

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Publication details

The article was received on 15 Oct 2018, accepted on 16 Nov 2018 and first published on 17 Nov 2018


Article type: Paper
DOI: 10.1039/C8CP06405A
Citation: Phys. Chem. Chem. Phys., 2019, Advance Article
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    Femtosecond electronic relaxation and real-time vibrational dynamics in 2′-hydroxychalcone

    Y. Yamakita, N. Yokoyama, B. Xue, N. Shiokawa, Y. Harabuchi, S. Maeda and T. Kobayashi, Phys. Chem. Chem. Phys., 2019, Advance Article , DOI: 10.1039/C8CP06405A

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