Computational design, synthesis and optoelectronic characterisation of thermally activated delayed fluorescent materials : donor-acceptor and multi-resonance designs

Abstract

This thesis concerns the study of organic TADF materials, focussing on donor-acceptor (D-A TADF) and multi-resonance (MR-TADF) emitters. Materials were developed in silico, they were then synthesized, characterized and finally tested in OLED devices.

Chapter 1 introduces the various radiative decay pathways available in electronically excited molecules from photoluminescence and electroluminescence. D-A TADF and MR-TADF emitters are discussed in detail.

Chapter 2 introduces the background behind the computational methods undertaken. These include Hartree Fock, coupled cluster and DFT.

Chapter 3 investigates the impact of donor dendrons in the TADF emitter 2CzPN. Donor extension improves kRISC but at the expense of increasing non-radiative pathways.

Chapter 4 discloses a new acceptor unit, BImPy, which is coupled to phenoxazine as a donor, with TADF observed. The torsion angle within the acceptor was modulated as a function of N-substitution, with 4 emitters studied.

In Chapter 5 a computational investigation of a series of 14 literature D-A TADF emitters is undertaken, with calculated T₁, T₂, S₁, ΔE[sub](ST), ΔE[sub](ST2) and ΔE[sub](T2T1) along with S₁, T₁ and T₂ excited state natures from DFT compared with SCS-CC2, with M06-2X and CAM-B3LYP performing well.

Chapter 6 presents an accurate method for computational modelling of MR-TADF, SCS-CC2. This method is then used to design two new MR-TADF emitters which were synthesized and their optoelectronic properties evaluated with OLEDs fabricated.

In Chapter 7 the calculated S₁, T₁ and ΔE[sub](ST) of 35 literature MR-TADF emitters from SCS-CC2 and TD(A)-DFT are compared with experimental values, with SCS-CC2 performing well. Using SCS-CC2 the properties of MR-TADF emitters are discussed and further studies of related INVEST materials and D-A emitters that contain a MR-TADF acceptors are undertaken.

Chapter 8 presents a new class of MR-TADF emitter without acceptor units designed using SCS-CC2. Modest TADF in doped films and high performing hyperfluorescent OLEDs are presented.