Engineering Metal Halide Perovskite Nanocrystals with BODIPY Dyes for Photosensitization and Photocatalytic Applications

The sensitization of surface-anchored organic dyes on semiconductor nanocrystals through energy transfer mechanisms has received increasing attention owing to their potential applications in photodynamic therapy, photocatalysis, and photon upconversion. Here, we investigate the sensitization mechanisms through visible-light excitation of two nanohybrids based on CsPbBr3 perovskite nanocrystals (NC) functionalized with borondipyrromethene (BODIPY) dyes, specifically 8-(4-carboxyphenyl)-1,3,5,7-tetramethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BDP) and 8-(4-carboxyphenyl)-2,6-diiodo-1,3,5,7-tetramethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (I2-BDP), named as NC@BDP and NC@I2-BDP, respectively. The ability of I2-BDP dyes to extract hot hole carriers from the perovskite nanocrystals is comprehensively investigated by combining steady-state and time-resolved fluorescence as well as femtosecond transient absorption spectroscopy with spectroelectrochemistry and quantum chemical theoretical calculations, which together provide a complete overview of the phenomena that take place in the nanohybrid. Förster resonance energy transfer (FRET) dominates (82%) the photosensitization of the singlet excited state of BDP in the NC@BDP nanohybrid with a rate constant of 3.8 ± 0.2 × 1010 s-1, while charge transfer (64%) mediated by an ultrafast charge transfer rate constant of 1.00 ± 0.08 × 1012 s-1 from hot states and hole transfer from the band edge is found to be mainly responsible for the photosensitization of the triplet excited state of I2-BDP in the NC@I2-BDP nanohybrid. These findings suggest that the NC@I2-BDP nanohybrid is a unique energy transfer photocatalyst for oxidizing α-terpinene to ascaridole through singlet oxygen formation.

The Dark Side of Lead-Free Metal Halide Nanocrystals: Substituent-Modulated Photocatalytic Activity in Benzyl Bromide Reduction

We illustrate here the high photocatalytic activity of sustainable lead-free metal halide nanocrystals (NCs), namely, Cs₃Sb₂Br₉ NCs, in the reduction of p-substituted benzyl bromides in the absence of a cocatalyst. The electronic properties of the benzyl bromide substituents and the substrate affinity to the NC surface determine the selectivity in C-C homocoupling under visible light irradiation. This photocatalyst can be reused for at least three cycles and preserves its good performance with a turnover number of ca. 105,000.

Revisiting the nontemplate approach for the synthesis of highly green emissive hybrid perovskite nanocrystals: platelets or spheres?

The long-standing debate about the morphology of colloidal methylammonium lead bromide perovskites nanocrystals, manufactured by our nontemplate synthetic strategy reported in 2014, is now resolved; specifically, the highest green emissive single nanoplatelets (of up to 93%) with long-term chemical and photochemical stability have been obtained after suitable purification steps.

Ruddlesden-Popper Hybrid Lead Bromide Perovskite Nanosheets of Phase Pure n=2: Stabilized Colloids Stored in the Solid State

Ruddlesden‐Popper lead halide perovskite (RP‐LHP) nano‐nanostructures can be regarded as self‐assembled quantum wells or superlattices of 3D perovskites with an intrinsic quantum well thickness of a single or a few (n=2‐4) lead halide layers; the quantum wells are separated by organic layers. They can be scaled down to a single quantum well dimension. Here, the preparation of highly (photo)chemical and colloidal stable hybrid LHP nanosheets (NSs) of ca. 7.4 μm lateral size and 2.5 nm quantum well height (thereby presenting a deep blue emission at ca. 440 nm), is reported for the first time. The NSs are close‐lying and they even interconnect when deposited on a substrate. Their synthesis is based on the use of the p‐toluenesulfonic acid/dodecylamine (pTS/DDA) ligand pair and their (photo)chemical stability and photoluminescence is enhanced by adding EuBr₂ nanodots (EuNDs). Strikingly, they can be preserved as a solid and stored for at least one year. The blue emissive colloid can be recovered from the solid as needed by simply dispersing the powder in toluene and then using it to prepare solid films, making them very promising candidates for manufacturing devices.

The synergy between the CsPbBr3 nanoparticle surface and the organic ligand becomes manifest in a demanding carbon–carbon coupling reaction

The cooperative action between the CsPbBr₃ surface and capping makes the photoredox homo-/cross-coupling of benzyl bromides under mild conditions possible.

Ultrathin lead bromide perovskite platelets spotted with europium(ii) bromide dots

We describe here the preparation of a novel nanohybrid comprising a two-layer cesium lead bromide nanoplatelet, [CsPbBr3]PbBr4 NPL, containing europium(ii) bromide (EuBr2) nanodots, by ultrasound/heating treatment of toluene dispersions of the CsPbBr3 nanomaterial in the presence of EuBr2 nanodots. The hybrid nanoplatelets exhibit strong excitonic and narrow emission peaks characteristic of ultrathin NPLs at 430 and 436 nm, respectively.

Colloids of Naked CH3NH3PbBr3 Perovskite Nanoparticles: Synthesis, Stability, and Thin Solid Film Deposition

A novel preparation of lead halide, CH₃NH₃PbBr₃, perovskite nanoparticle solid films from colloidal "naked" nanoparticles, that is, dispersible nanoparticles without any surfactant, is reported. The colloids are obtained by simply adding potassium ions, whose counterions are both more lipophilic and less coordinating than bromide ions, to the perovskite precursor solutions (CH₃NH₃Br/PbBr₂ in dimethylformamide) following the reprecipitation strategy. The naked nanoparticles exhibit a low tendency to aggregate in solution, and they effectively self-assembled on a substrate by centrifugation of the colloid, leading to homogeneous nanoparticle solid films with arbitrary thickness. These results are expected to spur further the interest in lead halide perovskites due to the new opportunities offered by these films.

Fe3O4@Au@mSiO2 as an enhancing nanoplatform for Rose Bengal photodynamic activity

A novel nanoplatform composed of three types of materials with different functionalities, specifically core-shell Fe₃O₄@Au nanoparticles encapsulated near the outer surface of mesoporous silica (mSiO₂) nanoparticles, has been successfully synthesised and used to enhance the efficiency of a photosensitiser, namely Rose Bengal, in singlet oxygen generation. Fe₃O₄ is responsible for the unusual location of the Fe₃O₄@Au nanoparticle, while the plasmonic shell acts as an optical antenna. In addition, the mesoporous silica matrix firmly encapsulates Rose Bengal by chemical bonding inside the pores, thus guaranteeing its photostability, and in turn making the nanosystem biocompatible. Moreover, the silica surface of the nanoplatform ensures further functionalisation on demand.