Gating upconversion electroluminescence in a single molecule via adsorption-induced interaction of unpaired spin

TL;DR

This study demonstrates that the adsorption geometry of a radical molecule on a surface can gate upconversion electroluminescence by reordering excited states, revealing new ways to tune spin-dependent molecular light emission.

Contribution

It shows how adsorption-induced interactions in a single radical molecule can control electroluminescence, a novel approach for tuning molecular spin-dependent phenomena.

Findings

Adsorption geometry affects unpaired electron interaction with substrate.

Upconversion electroluminescence is gated by molecular adsorption geometry.

State reordering enhances excited state transition probabilities.

Abstract

Molecules with unpaired spins (radicals) offer promising alternatives to closed-shell molecules as they are less limited regarding the spin statistics in their electroluminescence. Here, we combine scanning tunneling microscopy induced luminescence and density functional theory to study single vanadyl phthalocyanine molecules, which are stable neutral radicals. Two distinct adsorption geometries of the molecule on NaCl/Au(111) lead to a difference in the interaction of the unpaired electron with the substrate, which in turn allows us to investigate its effects on the light emission process. Remarkably, we observe that up-conversion electroluminescence is gated by the adsorption geometry of the molecule, an effect we attribute to a reordering of excited states and enhanced excited state transition probabilities. The profound influence of the unpaired electron via state reordering opens new possibilities for tuning not only molecular electroluminescence but also many other spin dependent phenomena.