Stable luminescent diphenylamine biphenylmethyl radicals with α-type D0 → D1 transition and antiferromagnetic properties

Abstract

Organic luminescent radicals, with their open-shell electronic structure, exhibit appealing optoelectronic properties and hold promise for a wide range of potential applications. Although a few series of luminescent radicals have been reported, most feature D₀ → D₁ transitions dominated by HOMOβ–SOMOβ (β-type transitions). In contrast, luminescent radicals that exhibit SOMOα–LUMOα properties (α-type transitions) are much rarer. Here, we designed and synthesized two stable novel diphenylamine biphenylmethyl (BTM) luminescent radicals, both characterized by α-type D₀ → D₁ transitions, and simultaneously maintained the D–A˙ structure for the first time. Density functional theory (DFT) calculations confirmed that fine-tuning the energy levels of frontier molecular orbitals can facilitate β-type to α-type D₀ → D₁ transition. Besides, in a 2(2Cl(m)PhN)-BTM crystal we for the first time observed strong antiferromagnetic interactions among luminescent radicals through SQUID measurements. This work offers design insights into luminescent radicals with α-type transition for future development.