Jump to main content
Jump to site search
Access to RSC content Close the message box

Continue to access RSC content when you are not at your institution. Follow our step-by-step guide.


Issue 3, 2016
Previous Article Next Article

Protonated thiophene-based oligomers as formed within zeolites: understanding their electron delocalization and aromaticity

Author affiliations

Abstract

In an earlier work, protonated thiophene-based oligomers were identified inside ZSM-5 zeolites. The novel compounds exhibited π–π* absorption wavelengths deep within the visible region, earmarking them for possible use as chromophores in a variety of applications. In this computational study, we determine the factors that cause such low-energy transitions, and describe the electronic structure of these remarkable compounds. DFT calculations of conjugated thiophene-based oligomers with up to five monomer units reveal that the main absorption band of each protonated oligomer is strongly red-shifted compared to the unprotonated form. This effect is counterintuitive, since protonation is expected to diminish aromaticity, and thereby increase the HOMO–LUMO gap. We find that upon protonation the π-electrons remain delocalized over the entire π-conjugated molecule, but the positive charge is localized predominantly on the protonated side of the molecule. A possible explanation for this ground-state charge localization is the participation of the C–H bond in the π-system of the protonated ring, locally providing aromatic stabilization for the positive charge. The addition of the proton stabilizes all electronic orbitals, but due to the ground state π-electron distribution away from the added nucleus, the HOMO is stabilized less than the LUMO. The main absorption peak upon protonation corresponds to the charge transfer excitation involving the frontier orbitals, and the small band gap explains the observed red shift. Analogue calculations on thiophene within a ZSM-5 zeolite cluster model confirm the same trends upon protonation as observed in the non-interacting compounds. Understanding the electronic structure of these compounds is very relevant to correlate UV-Vis bands with acidic strength and possibly environment in zeolites and to improve their performance in catalytic and energy related applications.

Graphical abstract: Protonated thiophene-based oligomers as formed within zeolites: understanding their electron delocalization and aromaticity

Back to tab navigation

Supplementary files

Article information


Submitted
25 Oct 2015
Accepted
14 Dec 2015
First published
21 Dec 2015

This article is Open Access

Phys. Chem. Chem. Phys., 2016,18, 2080-2086
Article type
Paper
Author version available

Protonated thiophene-based oligomers as formed within zeolites: understanding their electron delocalization and aromaticity

D. Valencia, G. T. Whiting, R. E. Bulo and B. M. Weckhuysen, Phys. Chem. Chem. Phys., 2016, 18, 2080
DOI: 10.1039/C5CP06477E

This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence. Material from this article can be used in other publications provided that the correct acknowledgement is given with the reproduced material and it is not used for commercial purposes.

Reproduced material should be attributed as follows:

  • For reproduction of material from NJC:
    [Original citation] - Published by The Royal Society of Chemistry (RSC) on behalf of the Centre National de la Recherche Scientifique (CNRS) and the RSC.
  • For reproduction of material from PCCP:
    [Original citation] - Published by the PCCP Owner Societies.
  • For reproduction of material from PPS:
    [Original citation] - Published by The Royal Society of Chemistry (RSC) on behalf of the European Society for Photobiology, the European Photochemistry Association, and RSC.
  • For reproduction of material from all other RSC journals:
    [Original citation] - Published by The Royal Society of Chemistry.

Information about reproducing material from RSC articles with different licences is available on our Permission Requests page.


Social activity

Search articles by author

Spotlight

Advertisements