As an emerging type of optically active material, semiconductor nanocrystals (NCs) stabilized by chiral molecules have attracted much attention. Owing to the wide range of potential applications of chiral perovskite NCs, the development of these materials is of great importance, but there has been a lack of relevant studies. Here, we describe an investigation of the properties of chiral perovskite NCs obtained using post-synthetic ligand exchange (achiral ligand/chiral ligand). These are found to exhibit mirror-image circular dichroism spectra. It is the chirality of the ligand (enantiomeric 1,2-diaminocyclohexane, DACH) that is most likely responsible for the induction of chiroptical activity in these NCs. Furthermore, their chiroptical properties and the corresponding mechanisms are found to depend strongly on the amount of capping ligand. When excess DACH is used to cap the surface of the NCs, their chiroptical properties are induced mainly by aggregation of DACH on the surface in a chiral pattern. In contrast, when small amounts of DACH are used for the capping, it is mainly surface distortion (or defects) and electronic interaction mechanisms that contribute to the chiroptical behavior of the NCs. In both cases, the anisotropy factors of the NCs are of the order of 10−3, which is comparable to or larger than the values reported for other chiral semiconductor and metal NCs. This work opens the door toward further understanding of chiroptical perovskite NCs and their potential applications.

In-depth studies of nonradiative (NR) decay, seeking to maximize NR decay rate or manipulate other NR decay channels, are of greatest significance for improving the photothermal conversion efficiency (η) of organic materials for phototheranostics; however, to date, relevant work remains scarce. Here, we present an insightful study of NR decay in BODIPY (BDP) dye, in an aggregated state, i.e., in BDP nanoparticles (BDP NPs), which show an efficient additional NR decay channel from the aggregation-stabilized intermolecular charge transfer (CT) state, resulting in exceptionally high η (61%) for highly efficient phototheranostics in vivo. BDP NPs exhibit two ultrafast NR decay channels with ultrashort lifetimes of 1.7 and 50 ps, which is in stark contrast to the only S 1 → S 0 NR channel with a long lifetime of 373 ps in the isolated BDP dye. More importantly, the ultrafast NR channel (1.7 ps) in BDP NPs depletes a substantial portion of the excited-state population (71%), which accounts for its much better photothermal effect as compared with the isolated BDP dye. Finally, BDP NPs display a highly efficient photoacoustic imaging (PAI) guided photothermal therapy (PTT) of tumors in live mice. This study presents a deeper fundamental understanding of NR decay in organic materials, setting a valuable guideline that may be widely applicable to similar molecular structure to develop more advanced organic materials not only for photothermal-related applications.

Emerging CsPbX 3 (X ¼ Cl, Br, and I) perovskite nanocrystals (NCs) have been demonstrated to be efficient emitters with a high fluorescence quantum yield, making these materials interesting for optical applications as well as for fundamental physics. Interestingly, doping with transition metal ions has been extensively explored as a way of introducing new optical, electronic, and magnetic properties, making perovskite NCs much more functional than their undoped counterparts. However, there have been no reports regarding the nonlinear optical properties of transition metal ion doped perovskite NCs. Herein, by using femtosecond-transient absorption spectroscopy, we have determined the one-photon linear absorption cross-section ($1.42 Â 10 À14 cm 2) of Mn-doped CsPbCl 3 NCs ($11.7 6 1.8 nm size, $0.2% doping concentration, and $600 nm emission wavelength). More importantly, their nonlinear optical properties-in particular, the two-photon absorption (TPA) and resultant emission-were investigated. Notably, the NCs exhibit wavelength-dependent TPA with a maximum value up to $3.18 Â 10 5 GM at a wavelength of 720 nm. Our results indicate that Mn-doped CsPbCl 3 NCs show promise in nonlinear optical devices and multiphoton fluorescence lifetime imaging.

No abstract

Circularly polarized luminescence (CPL) has been under intense research for future applications in high-resolution 3D displays, smart sensors, and information technologies. Different types of CPL materials have been developed, but neither the handedness nor the asymmetrical luminescence degree can be inferred from the material composition or the components. CPL materials with switchable handedness or emission wavelength play an important role, reducing the need for repetitive bottom-up synthesis. Here, we have presented switchable CPL behaviors toward multiple reported stimuli, including light irradiation, host-guest interaction, metal ions, pH, solvent, temperature, etc. This summary and discussion of the effective stimuli is aimed to promote rational future material exploration and boost related multidisciplinary applications.

Rational architectural design and catalyst components are beneficial to improve the photoelectrochemical (PEC) performance. Herein, hierarchical SnS2/CuInS2 nanosheet heterostructure porous films were fabricated and decorated with C60 to form photocathodes for PEC water reduction. Large-size CuInS2 nanosheet films were first grown on transparent conducting glass to form substrate films. Then, small-size SnS2 nanosheets were epitaxially grown on both sides of the CuInS2 nanosheets to form uniform hierarchical porous laminar films. The addition of C60 on the surface of the SnS2/CuInS2 porous nanosheets effectively increased visible light absorption of the composite photocathode. Photoluminescence spectroscopy and impedance spectroscopy analyses indicated that the formation of a SnS2/CuInS2 heterojunction and decoration of C60 significantly increased the photocurrent density by promoting the electron–hole separation and decreasing the resistance to the transport of charge carriers. The hierarchical SnS2/CuInS2 nanosheet heterostructure porous films containing multiscale nanosheets and pore configurations can enlarge the surface area and enhance visible light utilization. These beneficial factors make the optimized C60-decorated SnS2/CuInS2 photocathode exhibit much higher photocathodic current (4.51 mA cm–2 at applied potential −0.45 V vs reversible hydrogen electrode ) and stability than the individual CuInS2 (2.58 mA cm–2) and SnS2 (1.92 mA cm–2) nanosheet film photocathodes. This study not only reveals the promise of C60-decorated hierarchical SnS2/CuInS2 nanosheet heterostructure porous film photocathodes for efficient solar energy harvesting and conversion but also provides rational guidelines in designing high-efficiency photoelectrodes from earth-abundant and low-cost materials allowing widely practical applications.

A boron-dipyrromethene (BODIPY) dye emitting in the near-infrared (NIR) I region (723 nm) exhibits strong saturable absorption at 680 nm and excellent three-photon fluorescence imaging in the NIR II (1665 nm) window.

Autofluorescence is a major challenge in complex tissue imaging when molecules present in the biological tissue compete with the fluorophore. This issue may be resolved by designing organic molecules with long fluorescence lifetimes. The present work reports the two-photon absorption (TPA) properties of a thermally activated delayed fluorescence (TADF) molecule with carbazole as the electron donor and dicyanobenzene as the electron acceptor (i.e., 4CzIPN). The results indicate that 4CzIPN exhibits a moderate TPA cross-section ($9 Â 10 À50 cm 4 s photon À1), high fluorescence quantum yield, and a long fluorescence lifetime ($1.47 ls). 4CzIPN was compactly encapsulated into an amphiphilic copolymer via nanoprecipitation to achieve water-soluble organic dots. Interestingly, 4CzIPN organic dots have been utilized in applications involving two-photon fluorescence lifetime imaging (FLIM). Our work aptly demonstrates that TADF molecules are promising candidates of nonlinear optical probes for developing next-generation multiphoton FLIM applications.