👤 Ryota Kabe

Circularly polarized luminescence (CPL) has attracted significant attention for applications in displays, data encryption, anti-counterfeiting, and bioimaging. However, extending the emission lifetime beyond the second timescale remains a challenge. Here, we report circularly polarized long-persistent luminescence (CP-LPL) and the first evidence of circularly polarized photostimulated luminescence (CP-PSL) in purely organic systems. Using the chiral emitter R/S-OBN-Cz, we establish two complementary design strategies: (i) a three-component Förster resonance energy transfer (FRET) system, where the energy of long-lived charge-separated states between the donor and the acceptor is transferred to the chiral dopant, and (ii) a two-component upconversion system, where the locally excited state of chiral emitter is restored upon charge recombination. Both approaches result in CP-LPL with mirror-image CPL signals. Moreover, in the three-component FRET system, trapped charges in the chiral dopant can be released upon near-infrared stimulation, regenerating circularly polarized emission. This work establishes new proof of concept in chiroptical materials research, paving the way toward the practical applications in encrypted optical storage and advanced photonic devices. Show less

Long-persistent luminescent (LPL) materials store photon energy as charges and emit light over extended periods via charge recombination. LPL decay typically follows a power law rather than an exponential decay, enabling confirmation of charge accumulation from emission decay characteristics. While charge generation in organic materials has been widely studied at donor-acceptor (D/A) interfaces, it remains underexplored in single-component luminescent materials. Here, we investigate charge generation in organic solids by dispersing a luminescent molecule in various hosts and performing slow transient emission analyses. This approach enables the evaluation of ionization through accumulated triplet excited states and the detection of weak charge accumulation, which are difficult to capture using conventional transient techniques. Our results show that ionization in single-component materials proceeds through resonance-enhanced multiphoton ionization, although it is less efficient than at D/A interfaces. This approach provides insight into long-term photophysical and photochemical processes such as photodegradation. Show less

Long-persistent luminescence (LPL) materials have applications from safety signage to bioimaging; however, existing organic LPL (OLPL) systems do not align with human scotopic vision, which is sensitive to blue light. We present a strategy to blueshift the emissions in binary OLPL systems by upconverting the charge-transfer (CT) to a locally excited (LE) singlet state. Through rigorous steady-state and time-resolved photoluminescence spectroscopy and wavelength-resolved thermoluminescence measurements, we provide the direct experimental evidence for this upconversion in OLPL systems featuring small energy offsets between the lowest-energy CT and LE singlet states. These systems exhibited strong room temperature LPL, particularly when extrinsic electron traps are added. Importantly, the developed OLPL system achieved Class A (ISO 17398) LPL, matching well with human scotopic vision. The findings not only elucidate the role of small energy offsets in modulating LPL but also provide potential avenues for enhancing the efficiency and applicability of OLPL materials. Show less

Organic materials exhibiting long-lasting emission in the near infrared are expected to have applications in bio-imaging and other areas. Although room temperature phosphorescence and thermally activated delayed fluorescence display long-lived emission of approximately one minute, organic long-persistent luminescence (OLPL) systems with a similar emission mechanism to inorganic persistent emitters can emit for several hours at room temperature. In particular OLPL with a hole-diffusion mechanism can function even in the presence of oxygen. However, ionic materials lack long-term stability in neutral organic host owing to aggregation and phase separation. In this study, we synthesized polymers with stable near-infrared persistent luminescence at room temperature via the copolymerization of electron donors and acceptors. The copolymers exhibit long-persistent luminescence (LPL) at temperatures below the glass transition temperature and can be excited by approximately the entire range of visible light. LPL properties and spectra can be controlled by the dopant. Show less