Jump to main content
Jump to site search
PLANNED MAINTENANCE Close the message box

Scheduled maintenance upgrade on Thursday 4th of May 2017 from 8.00am to 9.00am (BST).

During this time our websites will be offline temporarily. If you have any questions please use the feedback button on this page. We apologise for any inconvenience this might cause and thank you for your patience.

Issue 7, 2012
Previous Article Next Article

Ultrafast relaxation of charge-transfer excitons in low-bandgap conjugated copolymers

Author affiliations


A photophysical study, employing linear optical and femtosecond two-dimensional electronic spectroscopies, of two conjugated copolymers in solution is reported. The study focuses on the effect of backbone conformation on the properties and dynamics of excitons. For the predominantly planar copolymer, poly((4,8-diethylhexyloxyl) benzo([1,2-b:4,5-b′]dithiophene)-2,6-diyl)-alt-((5-octylthieno[3,4-c]pyrrole-4,6-dione)-1,3-diyl) (PBDTTPD), the dipole moment of excitons was found to be unchanged upon photoexcitation, and no excitonic relaxation was detected within 1 ps. For poly[N-11′′-henicosanyl-2,7-carbazole-alt-5,5-(4′,7′-di-thienyl-2′.1′.3′-benzothiadiazole)] (PCDTBT), however, bathochromic shifts of the absorption and fluorescence spectra as a function of solvent polarity indicate a change in dipole moment of approximately 3 Debye upon photoexcitation at the red-edge of the absorption spectrum. Excitation at the PCDTBT absorption maximum, where an ensemble of polymer chains have a predominantly twisted backbone, causes relaxation in the excited state to excitons with stronger charge-transfer character on a timescale of ∼200 fs. This dynamic Stokes shift was not observed when exciting on the PCDTBT absorption red edge, which photo-selects more planar conformations. Ultrafast relaxation in the excited state involving coupled torsional and solvent coordinates increases the charge-transfer character of the exciton. Although there is a concomitant loss of energy, electron-hole correlation (binding) is weakened, which may contribute to the efficiency of organic solar cells based on PCDTBT as an electron donor.

Graphical abstract: Ultrafast relaxation of charge-transfer excitons in low-bandgap conjugated copolymers

Back to tab navigation
Please wait while Download options loads

Publication details

The article was received on 17 Jan 2012, accepted on 05 Apr 2012 and first published on 05 Apr 2012

Article type: Edge Article
DOI: 10.1039/C2SC20078C
Citation: Chem. Sci., 2012,3, 2270-2277
  •   Request permissions

    Ultrafast relaxation of charge-transfer excitons in low-bandgap conjugated copolymers

    I. Hwang, S. Beaupré, M. Leclerc and G. D. Scholes, Chem. Sci., 2012, 3, 2270
    DOI: 10.1039/C2SC20078C

Search articles by author