2605-01-8Relevant academic research and scientific papers
Application of Time-Dependent Raman Theory to Raman Excitation Profiles of Hexamethylbenzene-Tetracyanoethylene Electron Donor-Acceptor Complex
Britt, B.Mark,McHale, Jeanne L.,Friedrich, Donald M.
, p. 6347 - 6355 (1995)
Raman excitation and absorption profiles were obtained for the 1:1 electron donor-acceptor complex of hexamethylbenzene with tetracyanoethylene in dichloromethane solution.The absorption and Raman profiles were analyzed using the time-dependent theory of Heller to obtain the displacements and non-Condon factors for the four strongest Raman modes, the electronic excitation energy, the transition dipole, and solvent linebroadening parameters.The results are compared to the data reported by Myers et al (J.Am.Chem.Soc. 1992, 114, 6208) for the same complex in carbon tetrachloride solution.Attempts to account for solvent effects on the normal-mode displacements in terms of the solvent local field lead are complicated by the effect of the solvent on the structure of the complex.We propose that in CH2Cl2 but not in CCl4, the complex adopts a low-symmetry ground-state geometry which permits vibronic coupling of the charge-transfer and locally excited (TCNE) states.
Optical and Resonance Raman Studies of the 1:1 and 2:1 Complexes of Hexamethylbenzene with Tetracyanoethylene
Smith, Morgan L.,McHale, Jeanne L.
, p. 4002 - 4007 (2007/10/02)
The electron donor-acceptor (EDA) complexes of hexamethylbenzene (HMB) and tetracyanoethylene (TCNE) have been studied by optical and resonance Raman spectroscopy in a variety of solvents.The visible absorption spectra of the 1:1 and 2:1 complexes in cyclohexane have been resolved by multiwavelength linear regression of concentration-dependent absorbance data. the resonance Raman spectra of CCl4, CH2Cl2, and cyclohexane solutions of HMB and TCNE have been obtained with 5145-Angstroem excitation.A low-frequency mode at 163-169 cm-1 is assigned to the first overtone of the donor-acceptor stretch, νDA.In cyclohexane, the second overtone of νDA is also observed, but is overlapped by an a2u out-of-plane bending vibration of the methyl groups of HMB, which becomes allowed in the 2:1 complex due to vibronic coupling.A simple molecular orbital picture of the bonding in the 1:1 and 2:1 complexes is proposed which explains the resolved visible spectra as well as the low-frequency Raman data.It is concluded that the second donor molecule is not bound by "charge-transfer" forces, and that, although the ground state 2:1 complex has D2h symmerty, the two D-A bonds are of unequal strngth.
