Sadahiro Masuo

Lead halide perovskite nanocrystals (PNCs) are promising energy donors for organic dyes, yet the factors determining whether Förster resonance energy transfer (FRET) or Dexter‐type electron‐exchange transfer (DET) dominates remain unclear. Here, we investigate energy transfer (ET) mechanisms in CsPbBr ₃ PNC–Cy3 linkages as a function of PNC size using ensemble spectroscopy and single‐PNC measurements. In small PNC–Cy3 linkages, the experimentally determined ET efficiencies from PL quenching and lifetime shortening agree well with theoretical FRET efficiencies, and the donor decay time matches the acceptor rise time, identifying FRET as the dominant pathway. In contrast, large PNC–Cy3 linkages exhibit ET efficiencies exceeding theoretical FRET values and a faster donor decay than the acceptor rise, with both dynamics much faster than expected for FRET, supporting the involvement of a stepwise DET pathway. PLQY analysis further indicates that a nonemissive quenching pathway competes with ET to Cy3 and supports a model in which stepwise DET is initiated by hole transfer from the PNC to Cy3, followed by electron transfer. Single‐PNC measurements corroborate the ensemble results. These findings reveal that PNC size controls the competition between FRET and DET by modulating the donor–acceptor distance, providing a design principle for selectively controlling ET pathways in PNC–dye assemblies.

Semiconductor quantum dots (QDs) represent a premier class of inorganic nanomaterials featuring tunable optical properties, including size- and composition-dependent light absorption and photoluminescence (PL). Recent research has focused on their highly ordered 2D and 3D assemblies, termed superlattices, which exhibit collective photophysical phenomena such as long-range exciton diffusion and superfluorescence. However, constructing lower-dimensional architectures, such as 1D arrays capable of directional energy transport, remains a formidable challenge. This difficulty arises because conventional QDs lack the intrinsic shape anisotropy required for anisotropic self-assembly. This Perspective highlights recent progress in fabricating 1D arrays from spherical and cubic QDs, with particular emphasis on rational scaffolding and templating strategies that enable precise structural control. Finally, we provide perspectives on the future design of nanoscale and mesoscale superstructures integrating organic and inorganic nanomaterials.

The emission photon statistics and blinking dynamics of lead halide perovskite nanocrystals (PNCs) are strongly influenced by quantum confinement, Auger recombination (AR), and carrier trapping, yet their direct correlation with nanocrystal size remains unresolved. Here, we correlate size and optical properties of individual CsPbI₃ PNCs by combining single-particle spectroscopy with atomic force microscopy. PNCs smaller than ∼12 nm exhibit pronounced quantum confinement, strong photon antibunching with g⁽²⁾(0) ≤ 0.2, and band-edge carrier blinking. As the size increases, the photoluminescence red shift weakens and g⁽²⁾(0) increases, approaching unity above ∼17 nm. Femtosecond transient absorption measurements reveal strongly suppresses AR in larger PNCs, while the dominant blinking mechanism shifts from the band-edge carrier to Auger blinking at ∼16–18 nm. These results establish design principles for stable quantum light emitters and size-tunable optoelectronic materials.

Although azobenzenes have the potential to possess both aggregation‐induced emission (AIE) and photoresponsivity, examples are still limited due to their low emission efficiency. Herein, we report a new supramolecular strategy utilizing a large molecular dipole moment to enhance emission efficiency in the aggregate state and to induce controllable crystal polymorphism, thereby demonstrating the first observation of azobenzene‐based whispering gallery mode (WGM) emission with multiple sharp peaks. While dipolar azobenzene monomers in toluene are non‐emissive, the drop‐cast film exhibits red emission under photoexcitation due to the AIE effect. Microscopic photoluminescence (PL) measurements revealed that the film comprises a mixture of crystals, with major red and minor near‐infrared (NIR) emissions. By tuning the recrystallization temperature in toluene, we successfully controlled the crystal polymorphism and revealed the PL properties of each form using time‐resolved PL spectroscopy and theoretical approaches. A direct transition from the NIR‐emissive crystal to the red‐emissive one was observed upon thermal annealing. Remarkably, the micro‐sized particles exhibited multiple sharp PL peaks due to the microresonator effect, attributed to WGM emission, and the WGM peak positions shifted upon photoirradiation. This work provides a fundamental principle for the creation of new photoresponsive WGM‐based materials.

Colloidal semiconductor quantum dots (QDs) can generate multiple excitons (MXs) within a single QD. Owing to their large absorption cross-section, efficient utilization of MX is anticipated for the development of light-harvesting systems. However, MXs typically undergo nonradiative decay via Auger recombination (AR). In this study, we investigated the possibility of energy transfer from the MXs in a single QD to multiple cyanine dyes (Cy3) adsorbed on the QD surface. Based on the linear relationship between the AR lifetime and QD volume, formamidinium lead bromide perovskite nanocrystals (PNCs) with three distinct size distributions were synthesized. Simultaneous measurements of emission photon correlations and individual pristine PNC sizes revealed that the probability of multiphoton emission increased in PNCs larger than 12 nm. This was attributed to a slowdown in the AR rate, which was evaluated by transient absorption spectroscopy. Subsequently, multiple Cy3 dyes were adsorbed onto the PNCs as energy acceptors to evaluate the transfer of energy from the MXs to multiple Cy3 dyes. Photon correlation measurements of Cy3 emission via energy transfer─induced by excitation of a single PNC─showed an increased probability of multiphoton emission in PNC-Cy3 systems with PNC sizes exceeding 12 nm. These findings indicate that multiple Cy3 dyes were excited and emitted via the energy transfer from MXs. Thus, we clearly demonstrate that energy transfer from MXs to multiple surface dyes is feasible using large-sized PNCs.

Investigation of the energy transfer (ET) between perovskite nanocrystals (PNCs) and organic dyes is crucial because PNCs are suitable donor materials for creating photosensitizer systems. In this study, we investigated the relationship between a singlet ET mechanism and spectral overlap using CsPbBr₃ PNC-cyanine dyes─Cy3 and Cy5. We prepared PNC-dye linkage systems and investigated the ET at the single-PNC levels. The results of our study reveal that efficient ET occurs via fluorescence resonance ET (FRET) in the PNC-Cy3 system. Even in the PNC-Cy5 system, where the spectral overlap integral is 1 order of magnitude smaller than in the PNC-Cy3 system, efficient ET is observed, suggesting the occurrence of Dexter-type ET (DET). These results clearly demonstrate the change in the ET mechanism between FRET and DET depending on the spectral overlap. These findings are important for understanding exciton dynamics in PNC-organic molecule hybrid systems.

A high‐order heterogeneous nanostructure (heterostructure) composed of semiconductor nanocrystals (NCs) and organic dye supramolecular aggregates can exhibit distinctive photophysical properties arising from the interaction between them and can activate multicomponent materials chemistry. Herein, the study demonstrates a hierarchical coaggregation pathway guiding a high‐order heterostructure composed of a cubic‐shaped perovskite NC and perylene bisimide derivative (PBI) aggregates. The final morphologies in their coaggregation are determined by the aggregation levels of PBI before mixing with NCs. While mixing of NCs with monomers or aged fibrous aggregates of PBI results in the formation of low‐order or phase‐separated coaggregates, respectively, a coaggregation of the NC with unaged sheet‐like aggregates of PBI afforded the high‐order heterostructure. In this heterostructure, one‐dimensionally arranged NC and aggregated PBI are alternately connected at several nanometer‐scale intervals, like Roman pavement. Moreover, photoluminescence spectra and time‐resolved measurements at single coaggregate levels indicate that the high‐order heterostructure exhibited more efficient fluorescence resonance energy transfer from the NC to PBI aggregates compared to the phase‐separated coaggregates.

Precise control of assembled structures of quantum dots (QDs) is crucial for realizing the desired photophysical properties, but this remains challenging. Especially, the one‐dimensional (1D) control is rare due to the nearly isotropic nature of QDs. Herein, we propose a novel strategy for controlling the 1D‐arrangement range of cubic perovskite QDs in solution based on the morphological modification of a supramolecular polymer (SP) template. The original template with a short and tangled fibrous structure is prepared in a low‐polarity solvent mixture via self‐assembly of a naphthalenediimide‐functionalized cholesterol derivative with an adhesion group for QDs. Mixing this template with QDs leads to the co‐aggregation into short‐range 1D‐arrays of QDs on the templates. Notably, subsequent heating and cooling of the co‐aggregate solution forms longer‐range 1D‐arrays of QDs with lateral growth, where arranged QDs are sandwiched between reconstructed SP templates. Furthermore, the longer‐range 1D‐array of QDs is achieved via an alternative route involving the pre‐organization of templates into longer and dispersed fibers by heating and cooling of the original template, succeeded by co‐assembly with QDs. Finally, we reveal continuous fluorescence resonance energy transfer between 1D‐arranged QDs by an in‐depth analysis of the photoluminescence decay curves.

Precise control of assembled structures of quantum dots (QDs) is crucial for realizing the desired photophysical properties, but this remains challenging. Especially, the one‐dimensional (1D) control is rare due to the nearly isotropic nature of QDs. Herein, we propose a novel strategy for controlling the 1D‐arrangement range of cubic perovskite QDs in solution based on the morphological modification of a supramolecular polymer (SP) template. The original template with a short and tangled fibrous structure is prepared in a low‐polarity solvent mixture via self‐assembly of a naphthalenediimide‐functionalized cholesterol derivative with an adhesion group for QDs. Mixing this template with QDs leads to the co‐aggregation into short‐range 1D‐arrays of QDs on the templates. Notably, subsequent heating and cooling of the co‐aggregate solution forms longer‐range 1D‐arrays of QDs with lateral growth, where arranged QDs are sandwiched between reconstructed SP templates. Furthermore, the longer‐range 1D‐array of QDs is achieved via an alternative route involving the pre‐organization of templates into longer and dispersed fibers by heating and cooling of the original template, succeeded by co‐assembly with QDs. Finally, we reveal continuous fluorescence resonance energy transfer between 1D‐arranged QDs by an in‐depth analysis of the photoluminescence decay curves.