NEAR-INFRARED EXCITATION OF RAMAN-SCATTERING IN POLY(1,6-BIS[N-CARBAZOLYL]-2,4-HEXADIYNE) SINGLE-CRYSTAL AT 1064 NM

Fourier transform (FT)-Raman spectra of ly(1,6-bis[N-carbazolyl]-2,4-h exadiyne)[poly(DCH)I single crystals have been measured using the exci tation wavelengths 1064.1 and 780 nm. These spectra are markedly super ior to those available hiterto, because of fluorescence elimination. U nexpectedly, they are essentially similar to the resonance spectra obt ained using excitation wavelengths in the visible spectral region, con sisting substantially of strong nu(C=C) and nu(C=C) peaks, with the sa me relative intensities. Near infrared (IR) reflectance spectra have b een used to characterise the long wavelength tail of the electronic ab sorption spectrum in the vicinity of 1000 nm, leading to the conclusio n that the high peak intensities in the FT-Raman spectra are unlikely to result from the resonance process. However, they are explicable in terms of pi-electron-phonon coupling. Low temperature measurements pro vide no evidence for Fermi resonance as the cause of four peaks in the v(C=C:) region of the spectrum. (C) 1997 Elsevier Science B.V.