Persistent functionalized triarylmethyl radicals: when spin meets chirality

For decades, persistent trityl radical derivatives have been the object of intense research in a wide variety of disciplines, ranging from fundamental to applied science, thanks to the versatility of their properties (magnetic, optical, redox, etc.) and their potential as multifunctional open-shell building blocks. Nonetheless, far from becoming less appealing after such extensive study, these propeller-shaped radicals are nowadays gaining momentum thanks to their intrinsic chirality, which arises from the clockwise or counterclockwise torsion of their aryl rings. Indeed, increasing attention is being devoted to the implications of combining this feature with other properties, such as magnetism, enabling applications such as EPR probes, spin-dependent electronic transport through the CISS effect, and quantum technologies. From an optical perspective, their performance as circularly polarized light emitters has emerged as one of the most promising research directions. In this review, we present the advances made in understanding and exploiting the handedness of trityl-based radicals, from tetrathiatriarylmethyl radicals to halogen-shielded derivatives. We will cover the evolution from intrinsic propeller chirality to more complex diastereomeric systems resulting from their functionalization with additional chiral centers, axes, and planes, as well as the incorporation of additional propeller units into multipropeller architectures or their involvement in chiral supramolecular assemblies. Finally, we will discuss how these advances are shaping emerging applications.