Purely Organic Emitters for Multiresonant Thermally Activated Delay Fluorescence: Design of Highly Efficient Sulfur and Selenium Derivatives

Multiresonance thermally activated delayed fluorescence (MRTADF) emitters based on nitrogen-and/or oxygen-substituted organoboron molecules can exhibit high photoluminescence quantum yields, color purity, and thermal and chemical stability. Therefore, these emitters have recently attracted great interest for application in organic light-emitting diodes (OLEDs). The compositional diversity of MR-TADF materials is, however, limited to the use mainly of nitrogen and oxygen as electron-rich heteroatoms. Here, we expand the chemical range of these materials by considering the replacement of the O atoms with either S or Se atoms, with the objective of enhancing spin-orbit coupling via the heavy-atom effect. We theoretically evaluate the influence of these substitutions on the emissive properties. We investigate three series of MR molecules with structural motifs based on the following: (i) DOBNA (5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene); (ii) OAB-ABP (5,12dioxa-8b-aza-16b,19b-diboraanthra[1,9-ab]benzo[j]perylene); and (iii) the variation of the positions of the chalcogen atoms within the OAB-ABP framework. The results of highly correlated quantum-chemical calculations show that the chemical nature and positions of the chalcogen atoms have a crucial impact on the photophysical properties. Several of the molecules incorporating sulfur or selenium are found to exhibit both high-energy emissive states and large reverse intersystem crossing rates, which makes them promising candidates as efficient deep-blue emitters.

Automated summary

Multiresonance thermally activated delayed fluorescence (MRTADF) emitters based on nitrogen-and/or oxygen-substituted organoboron molecules have attracted great interest for application in organic light-emitting diodes (OLEDs) due to their high photoluminescence quantum yields, color purity, and stability. This study expands the chemical range of MRTADF materials by considering the replacement of oxygen atoms with sulfur or selenium atoms, aiming to enhance spin-orbit coupling via the heavy-atom effect. Theoretical evaluation reveals that the chemical nature and positions of the chalcogen atoms significantly influence the emissive properties, making the molecules incorporating sulfur or selenium promising candidates for efficient deep-blue emitters.