Learning Radical Excited States from Sparse Data

TL;DR

This paper introduces a data-driven method to accurately predict excited states of organic radicals from limited experimental data, enhancing the design of radical-based optoelectronic devices.

Contribution

It presents a novel approach that learns excited state properties directly from experimental data using a semiempirical model, requiring less data than traditional machine learning methods.

Findings

Achieved RMS error of 0.24 eV for excited state energies.

Improved accuracy over existing semiempirical methods.

Validated model on newly synthesized radicals with low errors.

Abstract

Emissive organic radicals are currently of great interest for their potential use in the next generation of highly efficient organic light emitting diode (OLED) devices and as molecular qubits. However, simulating their optoelectronic properties is challenging, largely due to spin-contamination and the multireference character of their excited states. Here we present a data-driven approach where, for the first time, the excited electronic states of organic radicals are learned directly from experimental excited state data, using a much smaller amount of data than typically required by Machine Learning. We adopt ExROPPP, a fast and spin-pure semiempirical method for calculation of the excited states of radicals, as a surrogate physical model for which we learn the optimal set of parameters. To achieve this we compile the largest known database of organic radical geometries and their UV-vis data, which we use to train our model. Our trained model gives Root Mean Square (RMS) and mean absolute errors for excited state energies of 0.24 and 0.16 eV respectively, improving hugely over ExROPPP with literature parameters. Four new organic radicals are synthesised and we test the model on their spectra, finding even lower errors and similar correlation as for the testing set. This model paves the way for the high throughput discovery of next generation radical-based optoelectronics.