Coulombic control of charge transfer in luminescent radicals with long-lived quartet states

TL;DR

This paper establishes design principles for controlling charge transfer and quartet state formation in luminescent radicals, demonstrating how Coulombic tuning of electronic interactions influences luminescence efficiency and spin state dynamics.

Contribution

It introduces molecular design rules for efficient quartet generation in luminescent radicals by tuning Coulombic interactions and electronic coupling, advancing quantum material development.

Findings

Achieved 55% luminescence yield in a radical-carbazole-acene material.

94% of emitted excitons originate from quartet states at microsecond timescales.

Demonstrated Coulombic tuning of charge transfer states controls non-radiative decay and spin interconversion.

Abstract

Excitons in organic materials are emerging as an attractive platform for tunable quantum technologies. Structures with near-degenerate doublet and triplet excitations in linked trityl radical, acene and carbazole units can host quartet states. These high spin states can be coherently manipulated, and later decay radiatively via the radical doublet transition. However, this requires controlling the deexcitation pathways of all metastable states. Here we establish design rules for efficient quartet generation in luminescent radicals, using different connection arrangements of the molecular units. We discover that electronic coupling strength between these units dictates luminescence and quartet formation yields, particularly through the energetics of an acene-radical charge transfer state, which we tune Coulombically. This state acts as a source of non-radiative decay when acene-radical separation is small, but facilitates doublet-quartet spin interconversion when acene-radical separation is large. Using these rules we report a radical-carbazole-acene material with 55% luminescence yield, where 94% of emitting excitons originate from the quartet at microsecond times. This reveals the central role of molecular topology in luminescent quantum materials.