Freeman, David Martin Eric; (2018) Manipulating triplets in organic semiconductors. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Triplet states in organic semiconducting devices are often associated with loss processes. Radiative decay to the ground state is a spin disallowed process, which results in triplets in normal organic systems decaying primarily though non-radiative pathways. In OLEDs, where 75% of created excitons are triplets, this has a large impact on device efficiency. The work herein focusses on the synthesis of organic polymers that utilise triplet states in some useful fashion. This was first achieved through incorporation of a heavy metal in the polymer chain, which increased spin-orbit coupling and allowed phosphorescence to occur. The heavy metal was incorporated directly into the polymer backbone as part of a porphyrin complex. Focus then moved to organic polymers that have decreased first excited singlet-triplet energy gaps. This allows excitons to move from singlet to triplet state without the use of a heavy metal, a formally spin disallowed process. Thermally activated delayed fluorescence is observed in one polymer. All synthetic work carried out is linked by the aim of using triplet states usefully in a resultant device. While the applications of the devices may differ, all in some way use triplet states in the movement of energy through the electronic system of the polymer. It is hoped that some of this work may form the basis of new types of materials for organic semiconducting systems.

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