Photophysical Properties of Benzophenone Based TADF Emitters in Relation to Their Molecular Structure

Abstract

Thermally activated delayed fluorescence (TADF) materials are commonly used in various apparatus, including organic light emitting device (OLED)-based displays, as they remarkably improve the internal quantum efficiencies (IQE). Alt-hough there is a wide range of donor-acceptor based compounds possessing TADF properties, in this computational study we investigated TADF and some non-TADF chromophores, containing benzophenone or its structural derivatives as the acceptor core, together with various donor moieties. Following the computational modeling of the emitters, several excited state properties, such as the absorption spectra, singlet-triplet energy gaps (∆EST), natural transition orbitals (NTO) and the topological ΦS indices, have been computed. Along with the donor-acceptor torsion angles and spin-orbit coupling (SOC) values, these descriptors have been utilized to investigate potential TADF efficiency. Our study has shown that on the one hand, our photophysical/structural descriptors and computational methodologies predict the experi-mental results quite well, on the other hand, our extensive benchmark can be useful to pinpoint the most promising func-tionals and descriptors for the study of benzophenone based TADF emitters.

Computational descriptor analysis on excited state behaviours of a series of TADF and non-TADF compounds

“…Prior to the evaluation of all optical and photophysical properties, conformational analysis was performed using the Gaussian 16 software package 76 to characterize all possible conformers of the chosen TADF and non-TADF molecules. Density Functional Theory (DFT) calculations with the M06-2X 77,78 meta-hybrid functional and the 6-31+G(d,p) 75 basis set have been carried out to optimize the ground state conformers and the corresponding S 1 and T 1 geometries. However, all conformers are expected to share the same TDA behavior since the latter is mainly dictated by the twisting angle between donor and acceptor moieties or between the donor and bridge moieties, which are highly conserved in the conformational space.…”

“…79 In our previous study, the excited state properties obtained by taking into account all the possible conformers of TADF molecules have been proven identical to the ones of the lowest energy conformer. 75 Thus, we continue our analysis considering the lowest energy conformers of each molecule only (see Tables S1-S5, ESI †). The energy and nature of excited states are assessed at the B3LYP 80 /6-31+G(d,p), M06-2X/6-31+G(d,p), CAM-B3LYP 81 / 6-31+G(d,p), and wB97XD 82 /6-31+G(d,p) levels of theory, and 6-311++G(3df,3pd) 83 and 6-311++G(2d,2p) 84 basis sets were used, in all calculations, for sulfur and phosphorus atoms, respectively.…”

“…Our main goal in that contribution was to understand the photophysical properties of benzophenone emitters and their derivatives in terms of absorption spectra, charge separations in the excited states, DE ST gaps and SOC magnitude. 75 Here, on the other hand, we plan to extend the objectives of the previous study investigating TADF emitters with various acceptor moieties and propose a new, more general, computational strategy applicable to a large variety of TADF emitters. For this purpose, we analyzed the relationship between molecular structures and photophysical properties of a wide range of emitters by means of ab initio calculations.…”

Theoretical insights into molecular design of hot-exciton based thermally activated delayed fluorescence molecules

“…77 Spin-orbit coupling (SOC) values were estimated by TDA-DFT calculations with the wB97X hybrid functional using Amsterdam Density Functional (ADF) software package. [78][79][80][81][82][83] The Slater-type allelectron basis set (TZP) was used for these computations within the ADF software. The thermal vibration correlation function formalism implemented in MOMAP (Molecular Materials Property Prediction Package) was used to calculate the constants of radiative and non-radiative transition rates.…”

A Computational Descriptor Analysis on Excited State Behaviours of a Series of TADF and Non-TADF Compounds

“…In recent literature, this behavior of TADF molecules has been proven by the comparison of TDA properties from Boltzmann Distribution of different conformers and the properties of the lowest energy conformer. 80 Thus, we continue further analysis considering, only the lowest energy conformers of each molecule (see Tables S1-S5). The energy and nature of excited states are assessed at the B3LYP 81 /6-31+G(d,p), M06-2X/6-31+G(d,p), CAM-B3LYP 82 /6-31+G(d,p), wB97XD 83 /6-31+G(d,p) levels of theory, 6-311++G(3df,3pd) 84 and 6-311++G(2d,2p) 85 basis sets were used, in all calculations, for sulfur and phosphorus atoms, respectively.…”