All-in-One Theranostic Platforms: Deep-Red AIE Nanocrystals to Target Dual-Organelles for Efficient Photodynamic Therapy.

Aggregation-induced emission (AIE) nanoparticles have been widely applied in photodynamic therapy (PDT) over the past few years. However, amorphous nanoaggregates usually occur in their preparation, resulting in loose packing with disordered molecular structures. This still allows free intramolecular motions, thus leading to limited brightness and PDT efficiency. Herein, we report deep-red AIE nanocrystals (NCs) of DTPA-BS-F by following the facile method of nanoprecipitation. It is observed that DTPA-BS-F NCs possess not only a high photoluminescence quantum yield value of 8% in the deep-red region (600-850 nm) but also an impressive reactive oxygen species (ROS) generation efficiency of up to 69%. Moreover, DTPA-BS-F NCs targeting dual-organelles of lysosomes and nucleus to generate ROS are also achieved, thus boosting the PDT effect in cancer therapy both in vitro and in vivo. This work provides high-performance AIE NCs to simultaneously target two organelles for efficient photodynamic therapy, indicating their promising application in all-in-one theranostic platforms.

Synthesis and preparation of acid capped CdSe nanocrystals as successful adsorbent and photocatalyst for the removal of dyes from water and its statistical physics analysis.

In this study, mercaptosuccinic acid capped CdSe nanocrystals were successfully synthesized and used as photocatalyst for the effective removal of methylene blue (MB) inaqueous solution under visible light and sunlight irradiations including its analysis with statistical physics theory. Dye adsorption properties of these nanocrystals were investigated via experimental kinetics and equilibrium studies. These experimental data were modeled via the application of statistical physics theory to explain the corresponding adsorption mechanism and to characterize the steric and energetic parameters involved in the dye removal. A maximum adsorption capacity of 27.07 mg g-1 (80% of dye removal) was observed in 10 min using an initial concentration of 30 mg L-1. Statistical physics calculations indicated that the adsorption energy was lower than 40 kJ mol-1. It was also established that the dye adsorption was associated to the electrostatic interactions and hydrogen bonding where dye aggregation and multi-molecular adsorption were expected. Overall, the dye removal was a spontaneous, feasible and exothermic. It was concluded that adsorption properties of CdSe-MSA nanocrystals improved the dye photo-catalytic degradation efficiency under visible light thus achieving up to 80% degradation efficiency in 60 min. The synergic effect of adsorption and photo-catalytic degradation performance was mainly due to the surface area (136.43 m2 g-1), small size (3.7 nm), and structural defects (selenium vacancies Se, interstitial of cadmium ICd) of CdSe nanocrystals, which enhanced both the response of these nanomaterials to visible light and their photo-catalytic activity. In summary, these nanocrystals are promising materials to be used in wastewater treatment under sunlight for the removal of organic compounds like dyes.

Driving Organic Nanocrystals Dissolution Through Electrochemistry.

We have recently discussed how organic nanocrystal dissolution appears in different morphologies and the role of the solution pH in the crystal detriment process. We also highlighted the role of the local molecular chemistry in porphyrin nanocrystals having comparable structures: in water-based acid solutions, protonation of free-base porphyrin molecules is the driving force for crystal dissolution, whereas metal (ZnII ) porphyrin nanocrystals remain unperturbed. However, all porphyrin types, having an electron rich π-structure, can be electrochemically oxidized. In this scenario, a key question is: does electrochemistry represent a viable strategy to drive the dissolution of both free-base and metal porphyrin nanocrystals? In this work, by exploiting electrochemical atomic force microscopy (EC-AFM), we monitor in situ and in real time the dissolution of both free-base and metal porphyrin nanocrystals, as soon as molecules reach the oxidation potential, showing different regimes according to the applied EC potential.

Control over size, shape, and photonics of self-assembled organic nanocrystals.

The facile fabrication of free-floating organic nanocrystals (ONCs) was achieved via the kinetically controlled self-assembly of simple perylene diimide building blocks in aqueous medium. The ONCs have a thin rectangular shape, with an aspect ratio that is controlled by the content of the organic cosolvent (THF). The nanocrystals were characterized in solution by cryogenic transmission electron microscopy (cryo-TEM) and small-angle X-ray scattering. The ONCs retain their structure upon drying, as was evidenced by TEM and atom force microscopy. Photophysical studies, including femtosecond transient absorption spectroscopy, revealed a distinct influence of the ONC morphology on their photonic properties (excitation energy transfer was observed only in the high-aspect ONCs). Convenient control over the structure and function of organic nanocrystals can enhance their utility in new and developed technologies.

General and Scalable Approach to Bright, Stable, and Functional AIE Fluorogen Colloidal Nanocrystals for in Vivo Imaging.

Fluorescent nanoparticles built from aggregation-induced emission-active organic molecules (AIE-FONs) have emerged as powerful tools in life science research for in vivo bioimaging of organs, biosensing, and therapy. However, the practical use of such biotracers has been hindered owing to the difficulty of designing bright nanoparticles with controlled dimensions (typically below 200 nm), narrow size dispersity and long shelf stability. In this article, we present a very simple yet effective approach to produce monodisperse sub-200 nm AIE fluorescent organic solid dispersions with excellent redispersibility and colloidal stability in aqueous medium by combination of nanoprecipitation and freeze-drying procedures. By selecting polymer additives that simultaneously act as stabilizers, promoters of amorphous-crystalline transition, and functionalization/cross-linking platforms, we demonstrate a straightforward access to stable nanocrystalline FONs that exhibit significantly higher brightness than their amorphous precursors and constitute efficient probes for in vivo imaging of the normal and tumor vasculature. FONs design principles reported here are universal, applicable to a range of fluorophores with different chemical structures and crystallization abilities, and are suitable for high-throughput production and manufacturing of functional imaging probes.

Inter-Backbone Charge Transfer as Prerequisite for Long-Range Conductivity in Perylene Bisimide Hydrogels.

Hydrogelation, the self-assembly of molecules into soft, water-loaded networks, is one way to bridge the structural gap between single molecules and functional materials. The potential of hydrogels, such as those based on perylene bisimides, lies in their chemical, physical, optical, and electronic properties, which are governed by the supramolecular structure of the gel. However, the structural motifs and their precise role for long-range conductivity are yet to be explored. Here, we present a comprehensive structural picture of a perylene bisimide hydrogel, suggesting that its long-range conductivity is limited by charge transfer between electronic backbones. We reveal nanocrystalline ribbon-like structures as the electronic and structural backbone units between which charge transfer is mediated by polar solvent bridges. We exemplify this effect with sensing, where exposure to polar vapor enhances conductivity by 5 orders of magnitude, emphasizing the crucial role of the interplay between structural motif and surrounding medium for the rational design of devices based on nanocrystalline hydrogels.

Self-Assembled Hybrid Materials Based on Organic Nanocrystals and Carbon Nanotubes.

Organic crystalline materials are used as dyes/pigments, pharmaceuticals, and active components of photonic and electronic devices. There is great interest in integrating organic crystals with inorganic and carbon nanomaterials to create nanocomposites with enhanced properties. Such efforts are hampered by the difficulties in interfacing organic crystals with dissimilar materials. Here, an approach that employs organic nanocrystallization is presented to fabricate solution-processed organic nanocrystal/carbon nanotube (ONC/CNT) hybrid materials based on readily available organic dyes (perylene diimides (PDIs)) and carbon nanotubes. The hybrids are prepared by self-assembly in aqueous media to afford free-standing films with tunable CNT content. These exhibit excellent conductivities (as high as 5.78 ± 0.56 S m-1 ), and high thermal stability that are superior to common polymer/CNT hybrids. The color of the hybrids can be tuned by adding various PDI derivatives. ONC/CNT hybrids represent a novel class of nanocomposites, applicable as optoelectronic and conductive colorant materials.

Tailoring ultrasound-induced growth of perylene diimide nanowire crystals from solution by modification with poly(3-hexyl thiophene).

Tailoring nanocrystalline morphologies of organic semiconductors holds importance for organic electronics due to the influence of crystal characteristics on optoelectronic properties. Soluble additives that control crystal growth are commonly found in a variety of contexts such as biomineralization, pharmaceutical processing, and food science, while the use of ultrasound to modify crystal nucleation and growth has been routinely employed in producing crystals of food ingredients, biomolecules, pharmaceuticals, and inorganic materials. However, both methods have been applied to the growth of organic semiconductor crystals only in limited fashion. Here, we combine these two approaches to show that colloidally stable nanowire suspensions of a n-type small molecule, perylene diimide (PDI), can be prepared with well-controlled structures by sonocrystallization in the presence of a p-type polymer, poly(3-hexyl thiophene) (P3HT), as a soluble additive. By preferentially adsorbing on lateral crystal faces, P3HT dramatically reduces PDI crystal growth rate in the lateral directions relative to that along the nanowire axis, yielding nanocrystals with widths below 20 nm and narrow width distributions. With the use of uniform short PDI nanowires as seeds and extension with metastable solutions, controlled growth of PDI nanowires by "living crystallization" is demonstrated, providing access to narrowed length distributions and tailored branched crystal morphologies.