Pulsed EPR Spectroscopy of the Photoexcited Triplet States of Thiophene Oligomers in Frozen Solution

Abstract

We present a triplet EPR study on photoexcitations in two different series of well defined thiophene oligomers. The first series consists of the so-called ‘end-capped' oligothiophenes with chain length n = 2−6. In the second series dodecyl chains are linked to α-oligothiophenes with n = 3, 6, and 8. Measurements of the triplet EPR spectra were performed using pulsed EPR spectroscopy. The characteristic lineshape of the EPR spectra provides evidence that photoexcitation leads to molecular triplet states in all compounds. We determined the fine structure parameters D and E and the population of the triplet eigenfunctions P x , P y , P z performing spectra simulations. The chain length dependence and the conformation dependence are discussed.

Localization length scales of triplet excitons in singlet fission materials

“…This is because the dipolar interaction between electron and hole magnetic moments gives rise to an energy level splitting between the three triplet spin sublevels, even at zero external magnetic field, governed by the zero-field splitting 24 This characteristic zero-field splitting means that triplet excitons can be readily identified through magnetic resonance, providing a direct way of observing these optically dark states. [25][26][27][28] In addition, this interaction provides an estimate of the excitonic spin-spin localization lengthscale since the zero-field splitting parameters are determined by the dipolar coupling between spins, and hence act as a measure of their separation.…”

Localized triplet excitations and the effect of photo-oxidation in ladder-type poly(p-phenylene) and oligo(p-phenylene)

“…12͒ or C Ϸ30. 29,30 The parameter E quantifies the deviation of the triplet wave function from axial symmetry and by definition of D and E, ͉E͉р͉D͉/3. 27,31-33 .…”

“…27,30 These solutions yield the following characteristics of the full-field triplet powder spectrum:…”

Excitonic Coupling Strength and Coherence Length in the Singlet and Triplet Excited States of meso–meso Directly Linked Zn(II)porphyrin Arrays

“…[51, 53,54] The expected slow TET rates and the large difference between the triplet relaxation rates of the brominated and unbrominated porphyrin moieties give rise to multiexponential decay kinetics at low temperature in porphyrin arrays. To investigate the EET rates and the extent of coupling between porphyrin moieties, we adopted a similar kinetic scheme to that of the singlet excited states (Scheme 5).…”