Modulation of emission characteristics by donor substitution in Multiple Resonant Thermally Activated Delayed Fluorescent emitters

Abstract

Thermally Activated Delayed Fluorescence (TADF) is an emission phenomenon of paramount significance, owing to the fact that it renders access to the triplet excitons without the employment of heavy metals for enormous applications, especially in optoelectronics. However, owing to the substantial structural distortion in their excited state, imparted by the Intramolecular Charge Transfer (ICT) nature, the emission spectra of these compounds are typically broad, lowering the colour purity, which causes energy losses in optoelectronic devices. Addressing the aforementioned issue in this project, two molecules, comprising of quinolino[3,2,1-de]acridine-5,9 dione (QAO) as the core, are designed to exhibit charge transfer nature, wherein two kinds of donors, carbazole and diphenylamine, are incorporated respectively. The core moiety QAO is known to manifest Short Range Charge Transfer (SRCT) on account of the electronic density distribution brought about by the opposite mesomeric effects in their components and the SRCT prompts narrowing of the emission spectra. Preliminary results reveal that carbazole, being a weaker donor, imparts a reduced ICT character and, therefore, partially retains the SRCT nature, unlike diphenylamine, which induces an absolute ICT nature. Therefore, by establishing a trend in these compounds, investigation of the structure-property correspondence at the molecular level becomes feasible, facilitating tuning of the emission spectra for cutting-edge applications.