A Raman and DFT study of substituted triphenylamines for use as charge transfer materials in light emitting polymers

Light emitting polymers (LEPs) are poised to become the predominant display technology within this decade. Charge transfer materials (CTMs) within these LEPs are important as they aid the efficiency of the electroluminescence emitted from the devices. Since many of these materials are strong Raman scatterers, Raman microscopy would provide an ideal method for investigating CTMs in-situ in the polymer matrix. The Raman spectra of the widely used CTMs based on triphenylamines are assigned for three different substituted monomers and for selected dimers and trimers. Theoretical calculations using the hybrid BPW91 functional and split-valence polarised 6G(d) basis set were performed, and the Raman scattering frequencies calculated and compared with those from experimental materials. A good correlation was found between the computed and experimental frequencies for the monomers. The largest deficit was 29 cm21 for any clearly assigned band, and there was an average error of 9.4 cm21 for the five most intense bands. The experimental Raman spectrum of the dimer dimethyltriphenyldiamine (DMTPD) and the calculated Raman active vibrations of methyltriphenyldiamine (MTPD) show few significant changes compared to the monomer. Comparison of the experimental trimer spectra with monomer calculations also show that simplified DFT calculations may confidently be used for assigning many bands in larger polymeric CTMs. q 2004 Elsevier B.V. All rights reserved.