Unveiling the potential of nonconjugate linkers (sp3-cores) in through-space charge transfer emitters and host materials for thermally activated delayed fluorescence organic light emitting diodes

Abstract

Organic materials based on nonconjugate linkers (sp³ cores) have emerged as versatile components that serve as emitters and host materials in thermally activated delayed-fluorescence (TADF) organic light-emitting diodes (OLEDs). Nonconjugate linkers offer an excellent platform for molecular design by incorporating different donors and acceptors that tailor their optical and electronic properties. Charge transfer occurs between donors and acceptors through space (TSCT). This approach involves incorporating sp³ hybridized carbon atoms into the core of the molecular structure, disrupting the conjugation length and thereby impeding direct charge transfer between the donor and acceptor entities. Consequently, these distinctive linkers provide significant advantages for the development of blue emitters and high triplet energy host materials. Additionally, they enhance the solubility of the resulting molecules, thereby facilitating device fabrication via solution processing. Hence, there is an urgent need for a comprehensive review that describes in detail the design strategies and synthetic routes of both emitters and host materials (both small molecules/dendrimers and polymers) based on nonconjugate linkers. This review aims to provide a clear understanding of the design tactics and structure–property relationships of emitters and host materials based on nonconjugate linkers, along with their outcomes in TADF OLEDs reported to date. The chemical structures of all reported materials are presented in the schemes, and their key photophysical and electroluminescence performance data are tabulated. Finally, the existing challenges and future prospects in this field are discussed in the conclusion part.