Study Of The Photoinduced Dynamics Of 1,3-dithiole-2-thione And Its Derivatives

Over 20 years time, the organic sulfur-rich molecules such as dithiolene -Dmit and tetrathiafulvalenes derivatives are among the widely interesting developments, because they show a variety of properties in the preparation of organic optical and electrical materials. During this period , people have paid attention to tetrathiafulvalenes derivatives' study on how to improve the conductive properties of the charge-transfer complexes based on tetrathiafulvalene .With the in-depth developments of the supramolecular chemistry and molecular electronics, the molecules will increasingly play an important role in the study on functional structural units because of their special physical and chemical properties of electrochemical behavior, assembly features, easy to derivatives and so on. Therefore we feel very interested in the study on the 1, 3-dithioles which are important precursors in the synthesis of a number of tetrathiafulvalenes derivatives .In this paper, the short-time photo-induced dynamics of the tetrathiafulvalenes derivatives' precursors-ethylene trithiocarbonate, 1,3-dithiole-2-thione,dimethyl 1, 3-dithiole-2-thione -4,5-dicarboxylate and 4,5-Ethylenedithio-1,3-dithiole-2-thione in the appropriate solvent have been investigated by the Resonance Raman spectra in combination with DFT calculation. Main contributions of the present work are summarized as follows:(1) Resonance Raman spectra of ethylene trithiocarbonate were obtained with 282.4, 299.1, 309.1 and 319.9 nm excitation wavelengths that probe respectively the (n,σ*) and the 1(Ï€,Ï€*) potential energy surfaces. The results indicate that clearly the spectra obtained at different excitation wavelengths exhibit large variations in relative band intensity that reflects significant differences in the excited state structural dynamics. At first, we thus assign the A-band absoption of ethylene trithiocarbonate to theÏ€(C=S)→π* (C=S)electronic transition,and the resonance Raman spectra indicate that the short-time photo-induced dynamics in the Franck-Condon region occurs along the nominal C=S stretchÏ…₁₁ forms the largest overtone progressions and combination bands with the other four Franck–Condon active modes the nominal S–C–S symmetric stretchÏ…₁₈ , the nominal H-C-C scissor + C-C stretchÏ…₉, the nominal S-C-S scissor+ C-S-C in plane bendÏ…₂₁ , the overtone 2Ï…₁₉ of the nominal S=CS₂ out of plane deformation, the nominal H-C-C scissor + C-C stretchÏ…₉ . The B-band is different from the A-band, which is assigned to the n (C=S)→σ* (S-C-S) electronic transition. It appears that photoexcitation of ethylene trithiocarbonate in the B-band absorption causes larger motions among the C=S stretchÏ…₁₁, S-C-S symmetric stretchÏ…₁₈, the S-C-S asymmetric stretch + H-C-H rockÏ…₁₄, S-C-S scissor+C-S-C in plane bendÏ…₂₁, H-C-H wagÏ…₁₄, S=CS₂ out of plane deformationÏ…₁₉, C-S anti-symmetric stretch in S-C-C-SÏ…₁₆,C=S in plane wagÏ…₂₂ and S–C–S symmetric stretchν₁₅,; Secondly the A- and B-band resonance Raman spectra also display very different kinds of anti-symmetry vibrational modes in terms of local symmetry of S=CS₂ functional group. The B-band resonance Raman spectrum (282.4 nm) shows the antisymmetric mode that are the nominal S–C–S asymmetric stretch + H-C-H rockÏ…₁₄ and the nominal C-S anti-symmetric stretch in S-C-C-SÏ…₁₆, while the A-band resonance Raman spectrum (309.1 and 319.9 nm) shows even overtones 2Ï…₁₉ and 4Ï…₁₉ of a antisymmetric modes that is the nominal out of plane S=CS₂ deformationÏ…₁₉ . The appearance of the even overtones 2Ï…₁₉ and 4Ï…₁₉ in A-band resonance Raman spectra indicates that the molecule upon A-band absorption or in S₃ excited state undergoes pyramidalization of carbon atom in S=CS₂ group, while the presence of the antisymmetric modes of the nominal S–C–S asymmetric stretch + H-C-H rockÏ…₁₄ and the nominal C-S symmetric stretch in S-C-C-SÏ…₁₆ indicates that the two C-S bonds undergo different bond length changes.(2) Resonance Raman spectra were acquired for 1,3-Dithiole-2-thione in cyclohexane solvent with 341.5, 354.7 and 368.9 nm excitation wavelengths. The resonance Raman spectra of these spectra indicate that most of the short-time photo-induced dynamics in the Franck-Condon region occurs mostly along the C=S stretch+ H-C=C-H scissorÏ…₄ , accompanied by the nominal H-C=C-H scissorÏ…₃ , the nominal S-C-S symmetric stretchÏ…₆ , the nominal C=C stretchÏ…₂ in A₁ irreducible representative, and one non-total symmetry S=C-SS out of plane deformation vibrational modeÏ…₁₁ in B₁ irreducible representative. This indicates that while most of the excited state structural dynamics are along the total symmetry vibrational reaction coordinates, it also moves along the non-total symmetry S=C-SS out of plane deformation reaction coordinate significantly, indicating the existence of the Franck-Condon region vibronic coupling between the A₁ and B₁ states. The appearance of the even overtones 2Ï…₁₁ and 4Ï…₁₁ of the nominal out of plane S=CS₂ deformationÏ…₁₁ suggests that geometry deformation or symmetry breaking occurs in the initial S2 excited state. This is very similar to the S3 state of ethylene or the S3 state of methyl xanthate anion.(3) We obtained the intensity absorption spectrum of dimethyl 1, 3-dithiole-2-thione -4,5-dicarboxylate in cyclohexane solvent which has a charge-transfer band near 355 nm. Resonance Raman spectra were acquired for dimethyl 1, 3-dithiole-2-thione -4,5-dicarboxylate in cyclohexane solvent with 341.5, 354.7 and 368.9 nm excitation wavelengths. The results indicate that the Franck-Condon region structural dynamics of dimethyl 1, 3-dithiole-2-thione -4,5-dicarboxylate have multidimensional character with motion predominantly in the C=S stretch (ν₁₂,|â–³| =1.05)and the C-S symmetric stretch modes in the S-C-S (ν₁₈,|â–³| =0.93), accompanied by moderate contributions from the C=C stretch(ν₂,|â–³| =0.23),the C=S stretch+ S-C symmetric stretch in C-C=C-C + O-CH₃ stretch(ν₁₃,|â–³| =0.53)and so on. The 75% total vibrational organizational enery (1081cm-1) of dimethyl 1, 3-dithiole-2-thione -4,5-dicarboxylate -dicarboxylate which is distributed on the modes about C=S stretch (ν₁₂,λ=597 cm-1)and the C-S symmetric stretch modes in the S-C-S (ν₁₈,λ=212 cm-1).(4) We obtained the intensity absorption spectrum of 4,5-Ethylenedithio-1,3-dithiole -2-thione in chloroform solvent which has a charge-transfer band near 400 nm. Resonance Raman spectra were acquired for 4,5-Ethylenedithio-1,3-dithiole-2-thione in chloroform solvent with 397.5 and 416nm excitation wavelengths. The results indicate that the Franck-Condon region structural dynamics of 4,5-Ethylenedithio-1,3-dithiole-2-thione have multidimensional character with motion predominantly in the C=C stretchν₃ and the C=C twist out of planeν₁₂, accompanied by moderate contributions from the C=S stretchν₁₃, C7-C 8stretchν₈,S-C-S anti-symmetric stretch +Ring deformation +H-C-H rockν₂₅, H-C-H twistν₂₃.