Solid-State Polymerization of the Unsymmetrically Substituted Diacetylene TS/FBS: Reaction Intermediates and Colour Zones

Chen

Vierheilig

et al. 2001

Self Cite

We review resonance Raman investigations of the linear conjugated p-electron system of polydiacetylenes embedded in single-crystalline monomer matrices. Absorption, luminescence, resonance Raman and resonance CARS spectroscopy were used to investigate vibronic properties of the polymers. As an example, we discuss the theoretical model applied for the simulation of the resonance Raman line and excitation profiles obtained from the polymer chains in FBS, TS/FBS and TS6 diacetylene single crystals. The theory is based on a Franck-Condon model, which considers a chain length dependence. The electronic transition energies and matrix elements were calculated by means of an LCAO MO (linear combination of atomic orbitals molecular orbital) calculation in the Hückel approach. An interaction between ensemble and intramolecular properties due to defects can be shown. Besides the well known polymer absorption, the partially polymerized single crystals of the diacetylenes under investigation show blue-shifted absorption bands in sharply separated crystal areas. The spectroscopic investigations of this chromism revealed that most probably growth defects in f111g crystal growth sectors influence the side-group geometry of the polymer chains. Using femtosecond time-resolved CARS spectroscopy, the dynamics of the vibrational excitation in the electronic ground and excited states can be investigated. Here, we report the controlled selective excitation of the polymers. We used a CARS scheme where the difference of pump and Stokes laser wavelengths is chosen to achieve resonance with several chain modes of the polydiacetylenes. By varying the timing and the phases of the femtosecond laser pulses, the timing and the intensity of these modes can be strongly influenced.

Section: Theory Resonance Raman Band Shape and Excitation Profilementioning

confidence: 99%

Section: Spectroscopy In the Wavenumber Domainmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

A review on linear and non‐linear resonance Raman spectroscopy of the conjugated system polydiacetylene

Chen

Vierheilig

et al. 2001

Self Cite

“…The result for Irrii is more complicated and contains several interference terms (see Eqn (16) at foot of page). By substituting Eqs (14)- (16) into Eqn (2) we obtain I x(3) l2 for the considered ensemble of molecules and hence the intensity of the CARS signal.…”

Section: Theorymentioning

confidence: 99%

Effect of homogeneous and inhomogeneous broadening on resonance CARS excitation profiles

Kiefer

1992

Self Cite

The influence of broadening due to intrinsic molecule and ensemble properties (homogeneous and inhomogeneous broadening) on kesonance CARS excitation profiles (CEPs) was investigated by means of a theoretical model. The non-linear susceptibility x(3) of a homogeneous ensemble of molecules was derived from perturbation theory using a Franck-Condon model and applying a crude Boro-oppenheimer approximation. Then it was assumed that these molecules are situated in an inhomogeneous environment which changes their electronic energies. The CARS intensity for this inhomogeneous ensemble was obtained from the homogeneous CARS intensity taking into account a distribution of energies. The influence of homogeneous and inhomogeneous broadening on CEPs was demonstrated by model calculations and compared with results obtained for resonance Raman excitation profiles. Possible applications are discussed. ~~

Resonance CARS spectroscopy on diacetylene single crystals

Leuchs

Michelis

et al. 1992

Self Cite

An experimental CARS set-up for resonant solid-state coherent spectroscopy is described. Resonance CARS spectra of one unsymmetrically (TSFBS) and two symmetrically (TS6, FBS) substituted diacetylene monomer single crystals, with a low content of polymer, were obtained with this apparatus. Particularly, spectra of the C-C and the C=C stretching vibrations of the polymer chains, recorded for different pump laser frequencies, were investigated. The occurrence of broad spectral CARS features which are non-resonant and Stokes shifted relative to other observed CARS lines is discussed.