The effect of oxidation on the structure of styryl-substituted sexithiophenes: A resonance Raman spectroscopy and density functional theory study

Abstract

The structures and vibrational properties of a series of styryl-substituted sexithiophenes and their charged species have been examined using resonance Raman spectroscopy in conjunction with density functional theory calculations. The calculated geometries of the radical cations and dications indicate that the quinoidal charged defects are more strongly localized in the center of the thiophene backbone than is observed in other sexithiophenes. This defect confinement, induced by the positions of the styryl substituents, is particularly evident in the dication species. However, the defect confinement weakens when alkoxy groups are added onto the phenyl rings by causing the extension of the charged defect into the styryl groups. The Raman spectra of the neutral styryl sexithiophenes are dominated by intense thiophene symmetrical stretching modes in both the measured and predicted spectra. Oxidation generates radical cations and dications, both of which can be observed in the solution state resonance Raman spectra. Unlike other sexithiophenes, which generally show a downshift of the intense thiophene stretching mode from the radical cation to the dication, a small upshift is observed for the styryl-substituted sexithiophenes. The theoretical spectra predict an insignificant change during this transition and the eigenvector for this mode reveals that it is localized over the same area occupied by the confined defect. In contrast, the solid state resonance Raman spectra of electrochemically oxidized films reveal evidence of solely radical cations and there is an appreciable downshift of the intense thiophene stretching mode compared with the corresponding mode in the solution spectra. This implies that the increase in the effective conjugation length from the solution to the solid state is greater for the radical cations than for the neutral species. It therefore appears that the radical cations form pi stacks in the solid film and the resulting intermolecular interactions effectively allow a further extension of the electron delocalization.

Indanedione-Substituted Poly(terthiophene)s: Processable Conducting Polymers with Intramolecular Charge Transfer Interactions

“…DFT calculations were performed using the Gaussian03 package. On the basis of previous studies on similar thiophene-based compounds, − we used a Becke-style three-parameter method with the Lee−Parr−Yang correlation functional (B3LYP) and a 6-31G(d) basis set. Optimized geometries were used to calculate the vibrational spectra (IR and Raman) so that these could be compared to experimental data.…”

A Synthetic, Structural, Spectroscopic and DFT study of ReI, CuI, RuII and IrIII Complexes Containing Functionalised Dipyrido[3,2‐a:2′,3′‐c]phenazine (dppz)

“…Solvents were obtained from Aldrich Chemicals. Resonance Raman spectra were generated with continuous‐wave excitation by using a system previously described 74. 75 Spectra were analysed with GRAMS AI (Galactic Industries) and Origin 7.5 (OriginLab Corp) software.…”

When “Donor–Acceptor” Dyes Delocalize: A Spectroscopic and Computational Study of D–A Dyes Using “Michler’s Base”

“…By comparing the bond lengths between the various compounds, also known as bond length alternation (BLA), subtle changes in the geometry can be explored. 92 This technique uses calculated geometries and assigns a bond numbering system (Figure S3). In this case, the bond numbering is defined from indandione (bond 1), through the linker, through donor 1, to terminate on donor 2 (bond 27).…”

“…By comparing the bond lengths between the various compounds, also known as bond length alternation (BLA), subtle changes in the geometry can be explored . This technique uses calculated geometries and assigns a bond numbering system (Figure S3).…”