High-Spin State Dynamics and Quintet-Mediated Emission in Intramolecular Singlet Fission

TL;DR

This study investigates high-spin states and quintet-mediated emission in intramolecular singlet fission systems, revealing the formation of pure quintet states and their role in delayed fluorescence, with implications for optoelectronic applications.

Contribution

It introduces spin-sensitive techniques to monitor and control high-spin states and emission pathways in DPH-based oligomers, highlighting the unique behavior of the trimer Me-(DPH)$_3$.

Findings

Pure quintet states form in all studied oligomers.

Quintet states dominate delayed fluorescence at room temperature.

The trimer Me-(DPH)$_3$ exhibits exclusively singlet fission pathways.

Abstract

High-spin states in molecular systems hold significant interest for a wide range of applications ranging from optoelectronics to quantum information and singlet fission (SF). Quintet and triplet states play crucial roles, particularly in SF systems, necessitating a precise monitoring and control of their spin dynamics. Spin states in intramolecular SF (iSF) are of particular interest, but tuning these systems to control triplet multiplication pathways has not been extensively studied. Additionally, whilst studies in this context focus on participation of triplet pathways leading to photoluminescence, emission pathways via quintet states remain largely unexplored. Here, we employ a set of unique spin-sensitive techniques to investigate high-spin state formation and emission in dimers and trimers comprising multiple diphenylhexatriene (DPH) units. We demonstrate the formation of pure quintet states in all these oligomers, with high-spin state optical emission via quintet states dominating delayed fluorescence up to room temperature. For triplet formation, we distinguish between the ability to form weakly exchange-coupled triplet pairs and the efficiency-reducing pathway of intersystem crossing (ISC), identifying the trimer Me-(DPH)$_3$ as the only oligomer exhibiting exclusively the desired SF pathways. Conversely, linear (DPH)$_3$ and (DPH)$_2$ show additional or exclusive triplet pathways via ISC. Our comprehensive analysis provides a detailed investigation into high-spin state formation, control, and emission in intramolecular singlet fission systems.