Laura Ratcliff, School of Chemistry, University of Bristol

Organic semiconductors have favourable properties for use in devices such as organic light emitting diodes (OLEDs), including low cost and light weight. The current generation of OLEDs are based on molecules containing heavy metals, motivating the use of purely organic molecules exhibiting thermally activated delayed fluorescence (TADF) for efficient and environmentally-friendly devices. A key property for TADF is a small singlet-triplet splitting, which, like ground state properties, can be strongly influenced by both the internal disorder and that of the surrounding environment. The effects of this disorder can be probed through density functional theory (DFT) simulations of large enough systems to study explicit environmental effects, which can necessitate new methods which are capable of treating large systems, while maintaining a high enough accuracy for both ground and excited state properties. This has motivated the development of a new method, named transition-based constrained DFT (T-CDFT), which aims to treat excited states in large systems and has been implemented within a linear scaling DFT framework. In this talk I will introduce T-CDFT, and show how it may be used in conjunction with other DFT-based approaches to explore disorder in core, valence and excited states of the prototypical TADF emitter 2CzPN.