Organic charge transfer complex towards functional optical materials

This year marks the 50th anniversary of a significant milestone in organic optoelectronics, i.e. , the first account of metallic-like conductivity in an entirely organic material, tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ). Since the discovery of this prototypical TTF-TCNQ charge-transfer (CT) pair, countless studies, ranging from various aspects, have been done on this fascinating TTF-TCNQ and related CT complexes. More recently, the CT complex-based approach has emerged as an elegant way of designing various next-generation functional organic materials, viz. room temperature phosphorescent (RTP), thermally activated delayed fluorescent (TADF), near infra infrared (NIR) emissive, organic spin-systems, etc. This highlight discusses how the synergy between computational screening and crystal engineering principles can be used to obtain the desired functional output and modulate the CT complex's bulk optical and electronic features. Emphasis is given to some of the recent non-covalent CT complex-based approaches to designing functional optical materials like RTP, TADF, NIR-emissive, chiral CT complex, etc. The article highlights the recent developments on some interesting optical traits of organic charge transfer complexes. Properties like room temperature phosphorescence, thermally activated delayed fluorescence, circularly polarised luminescence, etc. , are summarized.