Vibrational coupling in TADF and how molecular structure can control this complex triplet harvesting process (Conference Presentation)

Abstract

The process of triplet harvesting is by thermally activated delayed fluorescence, ‘TADF’, i.e. E-type delayed fluorescence, is now well established. In this talk I shall discuss how this triplet harvesting mechanism is affected by molecular architecture. Detailed photophysical measurements of intramolecular charge transfer (ICT) states have been made both in solution and solid state. Temperature dependent time resolved emission, delayed emission and photoinduced absorption are used to map the energy levels involved in molecule decay, and through detailed quantum chemical modelling, true electron exchange energies and other energy barriers of the systems are determined with the real states involved in the reversed intersystem crossing mechanism elucidated. Using the vibronic coupling second order spin orbit interaction we go on to show how both D-A-D molecule structure and conformation control TADF and efficiency in a TADF OLED. By confirming the vibronic coupling mechanism of rISC (and ISC) we can now start to think about true molecular design for TADF emitters. 1. Etherington, M. K., Gibson, J., Higginbotham, H. F., Penfold, T. J. & Monkman, A. P. Revealing the spin-vibronic coupling mechanism of thermally activated delayed fluorescence. Nat Commun 7, 13680 (2016). 2. Gibson, J., Monkman, A. P. & Penfold, T. J. The Importance of Vibronic Coupling for Efficient Reverse Intersystem Crossing in Thermally Activated Delayed Fluorescence Molecules. ChemPhysChem 1–7 (2016). doi:10.1002/cphc.201600662 3. Dias, F. B. et al. The Role of Local Triplet Excited States in Thermally-Activated Delayed Fluorescence: Photophysics and Devices. Adv. Sci. 3, 1600080 (2016).