[Paper Review] Optical read and write of spin states in organic diradicals

Rituparno Chowdhury, Petri Murto+18 more|arXiv (Cornell University)|Jun 5, 2024

Diamond and Carbon-based Materials Research5 citations

TL;DR

The paper demonstrates spin-optical addressability in a diradical molecule with two trityl groups, showing photoluminescence for singlet/triplet states, small ground-state spin exchange, and high photoluminescence yields enabling spin-photon interfacing.

ABSTRACT

Optical control and read-out of the ground state spin structure has been demonstrated for defect states in crystalline semiconductors, including the diamond NV- center, and these are promising systems for quantum technologies. Molecular organic semiconductors offer synthetic control of spin placement, in contrast to current limitations in these crystalline systems. Here we report the discovery of spin-optical addressability in a diradical molecule that comprises two trityl radical groups coupled via a fluorene bridge. We demonstrate the three important properties that enable operation as a spin-photon interface: (i) triplet and singlet spin states show photoluminescence peaked at 640 and 700 nm respectively; this allows easy optical measurement of ground state spin. (ii) the ground state spin exchange is small (~60 μeV) that allows preparation of ground state spin population. This can be achieved by spin-selective excited state intersystem crossing, and we report up to 8% microwave-driven contrast in photoluminescence. (iii) both singlet and triplet manifolds have near-unity photoluminescence quantum yield, which is in contrast to the near-zero quantum yields in prior reports of molecular diradicals. Our results establish these tuneable open-shell organic molecules as a platform to engineer tailor-made spin-optical interfaces.

Motivation & Objective

• Demonstrate optical control and read-out of ground state spin in an organic diradical system.
• Show spin-selective pathways enabling ground state spin preparation.
• Establish properties that enable spin-photon interface in tuneable organic molecules.

Proposed method

• Study a diradical molecule with two trityl radical groups linked by a fluorene bridge.
• Characterize photoluminescence for singlet and triplet manifolds at 700 nm and 640 nm respectively.
• Quantify ground state spin exchange and demonstrate spin-selective excited state intersystem crossing.
• Measure photoluminescence quantum yields for singlet and triplet manifolds.

Experimental results

Research questions

• RQ1 Can organic diradicals exhibit optically addressable spin states detectable via photoluminescence?
• RQ2 What are the key properties enabling a spin-photon interface in this molecular platform?
• RQ3 Is the ground state spin exchange sufficiently small to allow spin population preparation?
• RQ4 What is the efficiency (quantum yield) of photoluminescence for singlet and triplet manifolds?

Key findings

• Triplet and singlet states show photoluminescence peaks at 640 nm and 700 nm, enabling optical measurement of ground state spin.
• Ground state spin exchange is small (~60 μeV), enabling preparation of ground state spin population via spin-selective pathways.
• Both singlet and triplet manifolds have near-unity photoluminescence quantum yield.
• demonstrated up to 8% microwave-driven contrast in photoluminescence.
• These results position the diradical system as a tunable spin-photon interface in organic semiconductors.