Exciton-polaritons are quasiparticles with mixed photon and exciton character that demonstrate rich quantum phenomena, novel optoelectronic devices and the potential to modify chemical properties of materials. Organic semiconductors are of current interest for their room-temperature polariton formation. However, within organic optoelectronic devices, it is often the 'dark' spin-1 triplet excitons that dominate operation. These triplets have been largely ignored in treatments of polariton physics. Here we demonstrate polariton population from the triplet manifold via triplettriplet annihilation, leading to polariton emission that is longer-lived (>μs) even than exciton emission in bare films. This enhancement arises from spin-2 triplet-pair states, formed by singlet fission or triplet-triplet annihilation, feeding the polariton. This is possible due to state mixing, which -in the strong coupling regime-leads to sharing of photonic character with states that are formally non-emissive. Such 'photonic sharing' offers the enticing possibility of harvesting or manipulating even states that are formally dark.

Reaction centers (RCs) are the pivotal component of natural photosystems, converting solar energy into the potential difference between separated electrons and holes that is used to power much of biology. RCs from anoxygenic purple photosynthetic bacteria such as Rhodobacter sphaeroides only weakly absorb much of the visible region of the solar spectrum, which limits their overall light-harvesting capacity. For in vitro applications such as biohybrid photodevices, this deficiency can be addressed by effectively coupling RCs with synthetic light-harvesting materials. Here, we studied the time scale and efficiency of Förster resonance energy transfer (FRET) in a nanoconjugate assembled from a synthetic quantum dot (QD) antenna and a tailored RC engineered to be fluorescent. Time-correlated single-photon counting spectroscopy of biohybrid conjugates enabled the direct determination of FRET from QDs to attached RCs on a time scale of 26.6 ± 0.1 ns and with a high efficiency of 0.75 ± 0.01.

Advances in protein design and engineering have yielded peptide assemblies with enhanced and non-native functionalities.Here, various molecular organic semiconductors (OSCs), with known excitonic up-and down-conversion properties, are attached to a de novo-designed protein, conferring entirely novel functions on the peptide scaffolds. The protein-OSC complexes form similarly-sized, stable, water-soluble nanoparticles that are robust to cryogenic freezing and processing into the solidstate. The peptide matrix enables the formation of protein-OSC-trehalose glasses that fix the proteins in their folded states under oxygen-limited conditions. The encapsulation dramatically enhances the stability of protein-OSC complexes to photodamage, increasing the lifetime of the chromophores from several hours to more than 10 weeks under constant illumination. Comparison of the photophysical properties of astaxanthin aggregates in mixed-solvent systems and proteins shows that the peptide environment does not alter the underlying electronic processes of the incorporated materials, exemplified here by singlet exciton fission followed by separation into weakly-bound, localized triplets. The adaptable protein-based approach lays the foundation for spectroscopic assessment of a broad range of molecular OSCs in aqueous solutions and the solid-state, circumventing the laborious procedure of identifying the experimental conditions necessary for aggregate generation or film formation. The non-native protein functions also raise the prospect of future bio-compatible devices where peptide assemblies could complex with native and non-native systems to generate novel functional materials.

Diketopyrrolopyrroles are a popular class of electron-withdrawing unit in optoelectronic materials. When combined with electron donating side-chain functional groups such as thiophenes, they form a very broad class of donor-acceptor...