Quantitative evaluation of the preferential orientation ofpara-phenylene vinylene pentamers in polystyrene films by optically detected magnetic resonance

Abstract

The morphology of drop-casted and spin-coated films of blends ofpara-phenylene vinylenederived pentamers with polystyrene is investigated by means of X-band optically detected magnetic resonance (ODMR) of the triplet excited states. Adapting an electron spin resonance simulation prograto to ODMR, the orientation distribution function of the oligomers in the films could be quantified. After drop casting or spin coating the pentamers from a solution, the oligomers tend to lie with their backbones in the plane of the film. The parameters of film preparation and the type of pentamer strongly influence the orientation distribution function. Also, the study of preferentially oriented films allows for the correlation of principal directions of the zero-field splitting tensor with characteristic directions of the molecules.

Geminate and Nongeminate Recombination of Triplet Excitons Formed by Singlet Fission

“…The possibility that this anisotropy arises from preferential molecular orientation within the film [46] can be ruled out, since this would show a characteristic change of the line shapes as the film is rotated in the magnetic field, which we do not observe. The observed anisotropy is consistent, however, with anisotropic spin relaxation of thermalized triplets, due to a thermal modulation of the spin dipole-dipole interaction [47,48].…”

Ordering of PCDTBT Revealed by Time‐Resolved Electron Paramagnetic Resonance Spectroscopy of Its Triplet Excitons

“…[18] Given the high sensitivity of the shape of the triplet spectra to even slight preferential orientation of the molecules and the rather simple application of the method, TREPR opens up ap lethora of new possibilities to probe the local morphology not only of pristine polymers but especially of polymer blends prepared in the same way as those used in photovoltaic devices. Only one study used optically detected magnetic resonance (ODMR) at very low temperatures (2.5 K) to determine the orientation of small molecules in ap olystyrene matrix.…”

“…To the best of our knowledge, this is the first time TREPR has been used to probe the ordering of conjugated polymers. Only one study used optically detected magnetic resonance (ODMR) at very low temperatures (2.5 K) to determine the orientation of small molecules in a polystyrene matrix 18. Given the high sensitivity of the shape of the triplet spectra to even slight preferential orientation of the molecules and the rather simple application of the method, TREPR opens up a plethora of new possibilities to probe the local morphology not only of pristine polymers but especially of polymer blends prepared in the same way as those used in photovoltaic devices.…”

Zeitaufgelöste Elektronenspinresonanz‐Spektroskopie an Triplett‐Exzitonen deckt Ordnung von PCDTBT auf

“…Die vorliegende Studie ist unseres Wissens die erste Anwendung der TREPR‐Spektroskopie zur Untersuchung der Ordnung und Orientierung konjugierter Polymere. Lediglich eine Arbeit verwendete optisch detektierte magnetische Resonanz (ODMR) bei sehr tiefen Temperaturen (2.5 K), um die Orientierung kleiner Moleküle in einer Polystyrol‐Matrix zu untersuchen 18. Da die Form der Triplett‐Spektren schon gegenüber leichter Vorzugsorientierung der Moleküle sehr empfindlich und die Methode selbst verhältnismäßig einfach anwendbar ist, eröffnet die TREPR‐Spektroskopie eine ganze Reihe neuer Möglichkeiten, um die lokale Morphologie zu untersuchen – und das nicht nur von reinen Polymeren, sondern insbesondere auch von Polymer‐Blends, die auf die gleiche Weise hergestellt wurden wie jene in Solarzellen.…”