Theory and principles of luminescent organic radical materials for OLED and sensor applications

Project Information

LUMOR

Grant agreement ID: 101077649

DOI

10.3030/101077649

EC signature date 7 July 2023

Start date 1 January 2024

End date 31 December 2028

Funded under

• European Research Council (ERC)

Total cost

€ 1 500 000,00

EU contribution

€ 1 500 000,00

Coordinated by

LINKOPINGS UNIVERSITET
Sweden

Periodic Reporting for period 1 - LUMOR (Theory and principles of luminescent organic radical materials for OLED and sensor applications)

Reporting period: 2024-01-01 to 2026-06-30

Summary of the context and overall objectives of the project

Organic luminescent radicals (OLRs) represent a fundamentally new class of light emitting materials with the potential to reshape the landscape of organic optoelectronics, sensing technologies, and anti counterfeiting protection. Unlike conventional closed shell luminophores, OLRs exhibit spin allowed doublet–doublet emission, theoretically enabling internal quantum efficiencies up to 100%. Despite this promise, OLR photophysics remains poorly understood: the role of quartet excited states, the mechanisms of anti Kasha emission, and the conditions required for bright and stable luminescence are still largely unexplored. These knowledge gaps currently limit the performance of radical based OLEDs and hinder the development of next generation sensing and authentication materials.
The LumOR project aims to establish the first general theoretical and experimental framework for the photophysics of luminescent organic radicals and to apply this knowledge to three high impact technology sectors: (i) radical based OLEDs, (ii) ratiometric radical sensors, and (iii) two step anti counterfeiting systems. By combining advanced quantum chemical modelling with targeted synthesis and device fabrication, the project will uncover how quartet states can be harnessed to overcome spin statistical limitations in OLR OLEDs, design radicals capable of dual (doublet–doublet) emission for next generation ratiometric sensing of short lived radical species, and develop environmentally friendly aromatic carbonyls capable of photoinduced radical generation for multicolour, high security anti counterfeiting labels.
The expected impact of LUMOR is twofold. Scientifically, it will fill a major void in the fundamental theory of radical photophysics by establishing the mechanisms of doublet fluorescence, doublet–quartet intersystem crossing, multi channel anti Kasha emission, and radical specific sensing pathways. Technologically, the project targets breakthroughs in OLED efficiency beyond the current state of the art, highly selective radical probes capable of detecting species such as ROS on their natural ultrafast timescales, and robust two step authentication materials that activate luminescence only upon controlled irradiation, providing a new paradigm in document and product security.
Although the project is centred on physical chemistry, its applications in sensing, authentication, and materials design naturally intersect with societal and behavioural dimensions - particularly in the context of counterfeiting, product safety, and environmental sustainability. The project therefore integrates aspects of social sciences by addressing the needs of secure value chains and public trust in authentication systems, while also offering environmentally responsible alternatives to rare earth based inks.
Ultimately, LumOR sets the scientific foundation for future advances in radical based technologies, opening pathways toward sustainable lighting, advanced diagnostic tools, and secure information systems.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

During the project, substantial progress was made toward uncovering the photophysical principles and materials design strategies governing luminescent organic radicals. A major scientific achievement was the successful synthesis of heterocirculene based radicals featuring strong infrared absorption combined with pronounced anti Kasha doublet emission. These systems confirmed the theoretical prediction that higher lying doublet states in extended polyaromatic radicals can be selectively populated and radiatively deactivated, enabling efficient emission from electronically excited states that are normally non emissive in closed shell molecules. The new heterocirculene radicals also provided direct experimental validation for the role of molecular topology, spin delocalization, and packing induced stabilization in promoting the anti Kasha pathways targeted in the initial project proposal.
In parallel, the project led to the discovery of an unexpected new class of radicals derived from small aromatic molecules of biomass origin. These minimally substituted, environmentally benign precursors produced stable open shell species with unique optical signatures. Their ease of synthesis, natural abundance, and photostability mark them as promising candidates for green optoelectronic materials and sustainable sensing technologies. This also significantly broadened the chemical scope of luminescent radicals beyond traditional heavy aromatic scaffolds, demonstrating that even simple bio derived aromatics can host robust radical excited states when rationally activated.
A further achievement consisted of an in depth investigation of photoinduced radical formation in various condensed phase environments, with a particular focus on polymer matrices. Systematic spectroscopic and structural studies revealed how local rigidity, hydrogen bonding networks, polarity, and microphase separation modulate radical lifetimes, intersystem crossing channels, and emission yields. By comparing different polymer hosts, the project clarified the environmental factors required to stabilize radical intermediates against recombination and to enhance their radiative decay pathways. These insights provide essential design rules for embedding radicals in device relevant architectures, such as radical based OLEDs, ratiometric sensors, and photoresponsive anti counterfeiting labels.
Together, these achievements significantly advance the fundamental understanding of radical photophysics and establish new families of functional materials whose properties directly support the project's broader technological aims.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The project has generated results that substantially advance the scientific frontier of luminescent organic radicals and open new technological opportunities. A major breakthrough is the first successful synthesis of heterocirculene based radicals combining strong infrared absorption with detectable anti Kasha doublet emission. Prior to this work, efficient anti Kasha emission in radicals had been observed only in a few isolated systems with limited structural diversity. The newly developed heterocirculene radicals demonstrate that carefully engineered delocalization, topology, and excited state configuration can reliably produce higher state doublet emission, marking a clear step beyond the state of the art in both radical photophysics and molecular emitter design.
Equally transformative is the discovery of a previously unknown class of radicals derived from small aromatic molecules of biomass origin. Until now, radical emitters have largely relied on complex, synthetically demanding polyaromatics. Showing that simple, abundant, bio derived aromatics can form stable open shell emitters introduces an entirely new and sustainable materials platform. This opens the door to environmentally friendly radical-based optoelectronics, biodegradable sensors, and low cost authentication materials—none of which were achievable with existing radical families.
Another major advancement lies in the comprehensive investigation of photoinduced radicals embedded in polymer matrices and other condensed environments. While photoinduced radical generation had previously been demonstrated only in select host systems, this project elucidated the mechanistic influence of microenvironmental rigidity, hydrogen bonding, and polarity on radical stability and luminescence pathways. These insights provide the first systematic design rules for stabilizing short lived radical intermediates in solid-state architectures, enabling their integration into real devices such as OLEDs, ratiometric probes, and photoactivated security inks.
Together, these achievements reshape the fundamental understanding of radical photophysics and establish multiple new material classes with properties unattainable using conventional emitters. Their impact extends across organic electronics, sensing, sustainable chemistry, and anti counterfeiting technologies.
Looking forward, the key needs for further uptake include:
- deeper theoretical modelling of doublet–quartet interactions to optimize charge transport and emission efficiency in device architectures;
- extended synthetic exploration to diversify biomass derived radical precursors and tune their emission profiles;
- device level studies integrating the newly discovered radicals into OLEDs, sensors, and authentication platforms to validate performance at scale;
- long term stability and encapsulation studies to ensure robustness under operational conditions.