Excited state dynamics of organic semi-conducting materials

Abstract

Time-resolved absorption and emission spectroscopy has been applied to investigate the dynamics of excited state processes in oligomer models for semi-conducting organic materials. Following the photo-excitation of a pentamer oligomer that is a model for the conjugated polymer MEH-PPV, an ultrafast component of a few picoseconds is observed for the decay of the initially formed transient species. Variable temperature absorption and emission spectra combined with X-ray crystallography and calculations support the assignment of this rapid relaxation process to an excited state conformational rearrangement from non-planar to more planar molecular configurations. The implications of the results for the overall photophysics of conjugated polymers are considered.

The photophysics of phenylenevinylene oligomers and self-absorption of their fluorescence in polymer films

“…They point out this interpretation is consistent with the observation of the absorption spectrum of a MEH-PV tetramer and a pentamer in 2-methyltetrahydrofuran in a low temperature, glassy state having a spectral profile more like the usual shape for aromatic compounds with the most prominent vibronic transitions corresponding to those between the 0-0, 0-1 and 0-2 vibrational levels of the ground and first excited singlet states. 2,23,24 Another very similar model is also consistent with this low temperature absorption spectral shape as well as the absorp-Fig. 2 The absorption (solid lines) and fluorescence (dashed lines) spectra of MEH-PV oligomers in dioxane.…”

“…25,26 In the MEH-PV trimer characterized by Tilley et al, these energies for the four single bonds in the phenyl ring bridges lie within a range of 0.2 kcal mol −1 . 2,23,24 The relative populations of these twistomer configurations as a function of temperature will be governed by a Boltzman distribution. They point out this interpretation is consistent with the observation of the absorption spectrum of a MEH-PV tetramer and a pentamer in 2-methyltetrahydrofuran in a low temperature, glassy state having a spectral profile more like the usual shape for aromatic compounds with the most prominent vibronic transitions corresponding to those between the 0-0, 0-1 and 0-2 vibrational levels of the ground and first excited singlet states.…”

Mode specific excited state dynamics study of bis(phenylethynyl)benzene from ultrafast Raman loss spectroscopy

“…A deeper understanding of the photophysics, the energy transfer from the excited state, and the vibrational dynamics of such systems will be useful for designing opto-electronic devices. 3 Excited state dynamics of π-conjugated small organic molecules has been studied by many groups using time resolved a) Author to whom correspondence should be addressed. Electronic mail:…”

Effects of the rigid and sterically bulky structure of non-fused nonfullerene acceptors on transient photon-to-current dynamics

“…Aer photoexcitation, the structure of TT-T-DCI can relax to a more planar conformation within picoseconds. 78,79 In contrast, such conformational changes would be limited for TT-FT-DCI because it has a more rigid structure than TT-T-DCI.…”