Vibrational spectrum and molecular structure of triphenylamine monomer: A combined matrix-isolation FTIR and theoretical study

• Autor(a) principal: Reva, Igor
• Data de Publicação: 2003
• Outros Autores: Lapinski, Leszek, Chattopadhyay, Nitin, Fausto, Rui
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10316/17831; https://doi.org/10.1039/B306489A

Theoretical optimization of triphenylamine geometry, carried out at DFT(B3LYP) level using 6-31G** and aug-cc-pVDZ basis sets, predicted a propeller-like structure of the compound with D3 overall symmetry. In this structure, the central NCCC atoms are coplanar and the phenyl rings are symmetrically twisted from this plane by 41.5° (6-31G**) or 41.6° (aug-cc-pVDZ). The experimental FTIR spectrum of triphenylamine monomers isolated in an argon matrix was measured and interpreted by comparison with theoretical spectra calculated at the DFT(B3LYP) level with 6-31G** or aug-cc-pVDZ basis sets. The good agreement between the experimental and theoretical spectra allowed a positive assignment of the observed infrared absorption bands. Conformational flexibility of triphenylamine was investigated by carrying out a series of theoretical scans of the potential energy hypersurface of the system. Special attention was granted to the minimal energy pathway between the left-hand rotating and right-hand rotating symmetry identical structures of the compound. A route conserving a C2 symmetry axis was identified as implying an energy barrier of 20 kJ mol−1 only, whereas the calculated barrier for the concerted twist of all the phenyl rings (the route with conservation of the C3 symmetry axis) was as high as 54 kJ mol−1.