This work presents an analysis of the evolution of the molecular, vibrational and optical properties of a family of functionalized pentacenes. The analysis is performed on the basis of DFT quantum-chemical calculations in combination with spectroscopic techniques (Raman and UV-Vis). Theoretical calculations show that the bond length C-C/C=C alternation along the peripheral oligoenic ribbons increases with electron-releasing dioxolane substituents and diminishes with electron-withdrawing chlorine atoms and cyano groups. The attachment of triisopropylsilylethynyl groups increases the complexity of the Raman spectra. The spectra present many intense features of similar intensities in the 1,200-1,600 cm-1 range which are described by a combination of C-C/C=C stretching vibrations and in-plane C-H deformations spreading over the whole pentacene backbone. The absorption spectra display absorption bands in three different energy regions of the UV-Vis electromagnetic range. The spectra are dominated by a strong absorption band measured in the 300-350 nm region, which undergoes a sizeable red-shift with the substitution pattern, and a low-intensity, three-peak band in the 500-700 nm region, which undergoes a blue- or a red-shift depending on the electronic nature of the substituents. TDDFT calculations enable a detailed description of the trends observed in the absorption spectra.
|Number of pages||10|
|Journal||Theoretical Chemistry Accounts|
|State||Published - Feb 2011|
Bibliographical noteFunding Information:
This work was supported by the Ministerio de Ciencia e Inovación (MICINN) of Spain (projects CTQ2009-08790, CTQ2009-10098 and Consolider-Ingenio CSD2007–00010 in Molecular Nanoscience). The authors are also indebted to Junta de Andalucía for the project of excellence P09-FQM-4708 and grant FQM-159. The MICINN and UMA are also gratefully acknowledged by J.A. and R.M.O. for a FPI doctoral grant and a research grant, respectively.
- Density functional calculations
- Electronic transitions
- Raman spectra
ASJC Scopus subject areas
- Physical and Theoretical Chemistry