Spin fine-structure reveals bi-exciton geometry in an organic semiconductor

TL;DR

This paper uses broadband optically detected magnetic resonance to determine the local molecular geometry of bi-excitons in an organic semiconductor, linking spin structure to molecular pairing.

Contribution

It introduces a method to directly access bi-exciton geometry in organic semiconductors through magnetic resonance techniques.

Findings

Identification of the $S=2$ quintet bi-exciton state.

Correlation of spin structure with molecular crystal geometry.

Insights into bi-exciton formation and behavior.

Abstract

In organic semiconductors, bi-excitons are key intermediates in carrier-multiplication and exciton annihilation. Their local geometry governs their electronic properties and yet has been challenging to determine. Here, we access the structure of the recently discovered $S=2$ quintet bi-exciton state in an organic semiconductor using broadband optically detected magnetic resonance. We correlate the experimentally extracted spin structure with the molecular crystal geometry to identify the specific molecular pairings on which bi-exciton states reside.