Design of new thermally activated delayed fluorescence materials for oled applications using computational chemistry

Abstract

This study is a theoretical assessment of thermally activated delayed fluorescence (TADF) features of fourteen molecules. The analysis based on three different descriptors; the twisting angle (α), Φs index and ∆ES−T. The emitters are modelled by Density Functional Theory (DFT) at different levels of theories in vacuum. Conformational analyses that have been conducted at the most convenient level of theory revealed the most stable ground states geometries to be used in excited state investigations. The twisting angle (α) as a defining element of the rigidity, between donor (D) and acceptor (A) frameworks of molecules has been reported. Subsequently, the solvent effects have been taken into consideration at single point calculations in which excited state topolo gies have been analyzed by Time Dependent Density Functional Theory (TD-DFT) and Tamm-Dancoff Approximation (TDA) to show the charge transfer (CT) characters together with the alignment of frontier orbitals (FMOs) and ∆ES−T of compounds have been introduced. Population analysis of Natural Transition Orbitals (NTOs) have been performed by TDA and Φs indices were reported by two different charge distributions; Lo¨wdin and Mulliken. Lastly, the substitution effect of a conjugated moiety used for aggregation induced emission (AIE), namely AIEgens on non-TADF emitter was in vestigated. The descriptor analyses show that, (α) indicates the bulkiness of structures which gives rise to a highly twisted molecule with a suitable angle that directly effects the alignment of FMOs. The reported Φs values as indices reflecting the difference be tween the detachment and attachment densities, highly twisted structures have smaller values with a reduced orbital overlap which results in small ∆ES−T. Note that compounds with low twisting angles have high molecular overlap densities together with large singlet-triplet band gaps.