UV Absorption and Resonance Raman Spectra of 2,4-Dithiouracil

作者：Jin Ying-Chun; Zheng Xu-Ming^*

来源：Acta Physico - Chimica Sinica, 2017, 33(10): 1989-1997.

DOI：10.3866/PKU.WHXB201705175

• 2,4-Dithiouracil
• Excited state structural dynamics
• UV absorption spectrum
• Resonance Raman spectrum
• Density functional calculation

2,4-Dithiouracil is potentially an important photosensitizer for use in photodynamic therapy. Its photophysics when populated in the lowest excited state has been studied extensively. However, its higher light absorbing excited states and the corresponding reaction dynamics have not been investigated sufficiently. Herein, the resonance Raman spectroscopy and density functional theory were adopted to clarify the electronic transitions associated with the UV absorptions in the far-UV region and the short-time structural dynamics corresponding to the higher light absorbing excited states. The UV absorption spectrum in acetonitrile was deconvoluted into four bands: the moderate intense absorption band at 358 nm (f = 0.0336) (A band), the intense broad absorption bands at 338 nm (f = 0.1491), 301 nm (f = 0.1795), and 278 nm (f = 0.3532) (B, C, and D bands) respectively, on the basis of the relationship between the resonance Raman intensities and the oscillator strength f. The result was consistent with the predictions made using the time-dependent density functional theory calculations and the resonance Raman intensity patterns. Thus, the four bands resulted from the deconvolution are assigned as the S-0 -> S-2, S-0 -> S-6, S-0 -> S-7 and S-0 -> S-8 transitions, respectively. The resonance Raman spectra of the corresponding B, C, and D bands are assigned and the qualitative short-time structural dynamics are obtained. The major character in the short-time structural dynamics of 2,4-dithiouracil in the S-8 excited state is that a non-adiabatic process via S-8(pi pi*)/S(n pi*) curve-crossing, accompanied with ultrafast structural distortion, takes place in or near the Franck-Condon region, while the major character in the short-time structural dynamics in the S-7 and S-6 excited state appears in the multidimensional reaction coordinates, which are mostly along the C5C6/C2S8/C4S10/N2C3 bond lengths + C4N3H9/N1C2N3/C2N1C6/C6N1H7/C5C6H12 bond angles for the S-7 excited state and the C5C6/N3C2/C4S10/C2S8 bond lengths + C6N1H7/C5C6H12/C5C6N1/ C5C6H12/C2N1C6/N1C2N3/C4N3H9/N1C2N3 bond angles for the S-6 excited state.

• 出版日期2017-7-17
• 单位浙江理工大学