ARCHIMEDES · Approaching 20% emission efficiency in the NIR-II region with radical chromophores

The applications of light-based technologies in modern society cannot be underestimated. Some well-known examples of these include organic light-emitting diodes, fluorescent sensors, organic photovoltaics and fluorescence imaging. Emissive radicals have recently appeared as promising and entirely new building blocks for these technologies. This breakthrough is due to the fact that their electron spins at the lowest excited state and ground state are both doublets and the transition from the lowest excited state to the ground state is not hindered by being a spin-forbidden reaction which allows for higher operational efficiencies. Additionally, compared with both classical fluorescence microscopy and infrared imaging methods (750-900 nm), imaging in the second near-infrared window (NIR-II, 1000-1700 nm) allows for both deeper tissue penetration and a higher signal-to-noise ratio. The applicability of NIR-II emitters can be bolstered through combination with circularly polarized luminescence (CPL, the differential emission of left and right polarized light). The overarching goal of this project is to uncover a strategy to create radicals which at the same time: (a) strongly emit light in the NIR-II region; (b) are stable under ambient conditions; (c) strongly absorb light; (d) display large circularly polarized luminescence. The primary objective of ARCHIMEDES is to deliver breakthrough organic materials possessing large fluorescence quantum yields and stable radical structures in the integrated fields of molecular design, chromophore synthesis and fluorescence imaging of living cells. The realization of ARCHIMEDES will be based on both expanding the chemical space of stable, emissive C-centered radicals and on heretofore nonexisting emissive nitroxide radicals. The synergistic effects of increased brightness of NIR-II dyes and the higher sensitivity and resolution offered by CPL fluorophores will provide quality fluorescence imaging on a previously unthinkable level.