No abstract

Template free controlled aggregation and spectral properties in fluorescent organic nanoparticles (FONs) is highly desirable for various applications. Herein, we report a non-templated method for controlling the aggregation in NIR cyanine-based nanoparticles derived from a Group of Uniform Materials Based on Organic salts (GUMBOS). The cationic heptamethine cyanine dye, 1,1′,3,3,3′,3′-hexamethylindotricarbocyanine (HMT), was coupled with five different anions viz. [NTf2−], [BETI−], [TFPB], [AOT−] and [TFP4B] by ion exchange method to obtain the respective GUMBOS. The nanoGUMBOS obtained via a reprecipitation method were primarily amorphous and spherical (30-100 nm) as suggested by selected area electron diffraction (SAED) and transmission electron micrographs (TEM). The formation of tunable self-assemblies within the nanoGUMBOS was characterized using absorption and fluorescence spectroscopy, in conjunction with molecular dynamic simulations. Counterion controlled spectral properties observed in the nanoGUMBOS were attributed to variations in J/H ratios with different anions. Association with the anion [AOT−] afforded predominant J-aggregation enabling highest fluorescence intensity, while [TFP4B−] disabled the fluorescence due to predominant H-aggregation in the nanoparticles. Analyses of the stacking angle of the cations based on molecular dynamic simulation results in [HMT][NTf2], [HMT][BETI] and [HMT][AOT] dispersed in water and visual analysis of representative simulation snapshots also imply that the type of aggregation was controlled through the counterion associated with the dye cation.

Chemotherapeutic agents with low toxicity to normal tissues are a major goal in cancer research. In this regard, the therapeutic activities of cationic dyes, such as rhodamine 6G, toward cancer cells have been studied for decades with observed toxicities toward normal and cancer cells. Herein, we report rhodamine 6G-based organic salts with varying counter-anions that are stable under physiological conditions, display excellent fluorescence photostability, and more importantly have tunable chemotherapeutic properties. Our in-vitro studies indicate that the hydrophobic compounds of this series allow production of nanoparticles which are non-toxic to normal cells and toxic to cancer cells. Furthermore, the anions, in combination with cations such as sodium, were observed to be non-toxic to both normal and cancer cells. To the best of our knowledge, this is the first demonstration that both the cation and anion play an extremely important and cooperative role in the antitumor properties of these compounds.

No abstract

The ability to control the morphologies and spectral properties of organic low-dimensional nanomaterials is of paramount importance. The research reported herein demonstrates a template-free approach to tailored morphological and optical properties for a novel class of pseudoisocyanine (PIC)-based fluorescent organic nanoparticles derived from a group of uniform materials based on organic salts (GUMBOS). The synthesized nanoscale PIC-based particles (termed nanoGUMBOS), [PIC][NTf(2)] and [PIC][BETI], exhibit interesting adaptability as a function of the associated anion. The diamond-shaped nanostructures of [PIC][NTf(2)] and [PIC][BETI] nanorods exhibit enhanced fluorescence quantum yields relative to the parent compound, [PIC][I]. As supported by fluorescence lifetime measurements, these enhanced spectral properties can be attributed to differences in molecular self-assembly ordering (e.g., H- vs. J-aggregation) and restricted molecular rotation leading to reduced twisted intramolecular charge transfer in the nanoGUMBOS. The electrochemical properties of the PIC-based GUMBOS suggest their potential use in dye-sensitized solar cells.