Ionically Self-Assembled, Multi-Luminophore One-Dimensional Micro- and Nanoscale Aggregates of Thiacarbocyanine GUMBOS

Understanding of Förster Resonance Energy Transfer (FRET) in Ionic Materials

Herein, an ionic material (IM) with Förster Resonance Energy Transfer (FRET) characteristics is reported for the first time. The IM is designed by pairing a Nile Blue A cation (NBA⁺) with an anionic near-infrared (NIR) dye, IR820^-, using a facile ion exchange reaction. These two dyes absorb at different wavelength regions. In addition, NBA⁺ fluorescence emission spectrum overlaps with IR820^- absorption spectrum, which is one requirement for the occurrence of the FRET phenomenon. Therefore, the photophysical properties of the IM were studied in detail to investigate the FRET mechanism in IM for potential dye sensitized solar cell (DSSCs) application. Detailed examination of photophysical properties of parent compounds, a mixture of the parent compounds, and the IM revealed that the IM exhibits FRET characteristics, but not the mixture of two dyes. The presence of spectator counterion in the mixture hindered the FRET mechanism while in the IM, both dyes are in close proximity as an ion pair, thus exhibiting FRET. All FRET parameters such as spectral overlap integral, Förster distance, and FRET energy confirm the FRET characteristics of the IM. This article presents a simple synthesis of a compound with FRET properties which can be further used for a variety of applications.

Simple modification of basic dyes with bulky &symmetric WCAs for improving their solubilities in organic solvents without color change

A simple and easy solubility enhancement of basic dyes was performed with bulky and symmetric weakly coordinating anions (WCAs). The WCAs decreased the ionic character of the dyes by broadening the partial charge distribution and causing a screening effect on the ionic bonding. This new modification with WCAs has advantages in that it has no influence on the optical properties of the dyes. The solubilities of unmodified and modified dyes were tested in several organic solvents. X-ray powder diffraction patterns of the dyes were measured. Color films were prepared with the dyes and their color loci were analyzed to evaluate the optical properties. By the modification with WCAs, commercial basic dyes showed sufficient solubilities for be applied to various applications while preserving their superior optical properties.

2-Phenylbenzoxazole derivatives: a family of robust emitters of solid-state fluorescence

In addition to thermal, chemical and photochemical stability, the 2-phenylbenzoxazole fragment exhibits attractive emission properties in the solid state, thus leading to highly photoluminescent materials and sensors.

Tunable GUMBOS-based sensor array for label-free detection and discrimination of proteins

We report a sensor array approach, based on a novel group of 6-(p-toluidino)-2-naphthalenesulfonate (TNS)-based organic salts, for sensitive and label-free sensing of proteins.

A comparative study of nine berberine salts in the solid state: optimization of the photoluminescence and self-association properties through the choice of the anion

Counter-ions regulate the photoluminescence and self-association properties of berberine salts.

Improving energy relay dyes for dye-sensitized solar cells by use of a group of uniform materials based on organic salts (GUMBOS)

Energy relay dyes based on GUMBOS displayed improved characteristics in comparison to respective parent dyes including solubility and solar efficiency.

Fluorinated counterion-enhanced emission of rhodamine aggregates: ultrabright nanoparticles for bioimaging and light-harvesting

The key to ultrabright fluorescent nanomaterials is the control of dye emission in the aggregated state. Here, lipophilic rhodamine B derivatives are assembled into nanoparticles (NPs) using tetraphenylborate counterions with varied fluorination levels that should tune the short-range dye ordering. Counterion fluorination is found to drastically enhance the emission characteristics of these NPs. Highly fluorinated counterions produce 10-20 nm NPs containing >300 rhodamine dyes with a fluorescence quantum yield of 40-60% and a remarkably narrow emission band (34 nm), whereas, for other counterions, aggregation caused quenching with a weak broad-band emission is observed. NPs with the most fluorinated counterion (48 fluorines) are ∼40-fold brighter than quantum dots (QD585 at 532 nm excitation) in single-molecule microscopy, showing improved photostability and suppressed blinking. Due to exciton diffusion, revealed by fluorescence anisotropy, these NPs are efficient FRET donors to single cyanine-5 acceptors with a light-harvesting antenna effect reaching 200. Finally, NPs with the most fluorinated counterion are rather stable after entry into living cells, in contrast to their less fluorinated analogue. Thus, the present work shows the crucial role of counterion fluorination in achieving high fluorescence brightness and photostability, narrow-band emission, efficient energy transfer and high intracellular stability of nanomaterials for light harvesting and bioimaging applications.

Surfactant modulated aggregation induced enhancement of emission (AIEE)--a simple demonstration to maximize sensor activity

A new type of easily synthesized rhodamine-based chemosensor L(3), with potential NO2 donor atoms, selectively and rapidly recognizes Hg(2+) ions in the presence of all biologically relevant metal ions and toxic heavy metals. A very low detection limit (78 nM) along with cytoplasmic cell imaging applications with no or negligible cytotoxicity indicate good potential for in vitro/in vivo cell imaging studies. SEM and TEM studies reveal strongly agglomerated aggregations in the presence of 5 mM SDS which turn into isolated core shell microstructures in the presence of 9 mM SDS. The presence of SDS causes an enhanced quantum yield (φ) and stability constant (Kf) compared to those in the absence of SDS. Again, the FI of the [L(3)-Hg](2+) complex in an aqueous SDS (9 mM) medium is unprecedentedly enhanced (∼143 fold) compared to that in the absence of SDS. All of these observations clearly manifest in the enhanced rigidity of the [L(3)-Hg](2+) species in the micro-heterogeneous environment significantly restricting its dynamic movements. This phenomenon may be ascribed as an aggregation induced emission enhancement (AIEE). The fluorescence anisotropy assumes a maximum at 5 mM SDS due to strong trapping (sandwiching) of the doubly positively charged [L(3)-Hg](2+) complex between two co-facial laminar microstructures of SDS under pre-miceller conditions where there is a strong electrostatic interaction that causes an improved inhibition to dynamic movement of the probe-mercury complex. On increasing the SDS concentration there is a phase transition in the SDS microstructures and micellization starts to prevail at SDS ≥ 7.0 mM. The doubly positively charged [L(3)-Hg](2+) complex is trapped inside the hydrophobic inner core of the micelle which is apparent from the failure to quench the fluorescence of the complex on adding 10 equivalents of H2EDTA(2-) solution but in the absence of SDS it is quenched effectively.

Sodium Deoxycholate Hydrogels: Effects of Modifications on Gelation, Drug Release, and Nanotemplating

In the present study, sodium deoxycholate (NaDC) was used to produce gelation of tris(hydroxymethyl)amino-methane (TRIS) solutions above, below, and near the pKa of NaDC, respectively, which yielded a neutral gelator, a charged gelator, and a mixture of each. Impacts of ionic interactions on gel formation were studied in detail and showed that pH can be used to modify many hydrogel properties including sol-gel temperature, crystallinity, and mechanical strength. Several formulations yielded a unique rheological finding of two stable regions of elastic modulus. The release of a small molecule has been investigated under different hydrogel conditions and at variable shear rate, suggesting utility as a drug-delivery vehicle. It was also observed that pH modification of the hydrogels affected nanoparticle formation. Nanoparticles derived from a Group of Uniform Materials Based on Organic Salts (nanoGUMBOS), specifically cyanine-based NIR dyes, were templated within the hydrogel network for potential applications in tissue imaging. These nanoGUMBOS were found to be size-tunable, although material-dependent. Further understanding of NaDC/TRIS gelation has broadened the tunability and multidimensional applications of these tailored hydrogel systems.

Strategies for controlled synthesis of nanoparticles derived from a group of uniform materials based on organic salts

Over the past several years, nanomaterials derived from a group of uniform materials based on organic salts (GUMBOS) have been introduced into the scientific literature involving many analytical, biological, and technological applications. In this regard, these nanoGUMBOS have been shown to display a number of unique properties including fluorescence, magnetism, tumor targeting, and optoelectronic. To date, however, little focus has been placed on developing and refining approaches for generation of size-controlled nanoGUMBOS from GUMBOS building blocks. Herein, we describe a systematic effort to define various strategies for the production of well-defined nanoGUMBOS. Specifically, we describe methods based on (i) sonochemical, (ii) microwave-assisted, (iii) cyclodextrin-assisted, and (iv) surfactant-assisted syntheses of nanoGUMBOS, evaluating the efficiency of each technique in controlling the size, sphericity, and uniformity of nanoGUMBOS produced. The effect of systematic variation in experimental parameters such as concentration, cation-to-anion ratio, as well as presence and type of template introduced for formation of nanoGUMBOS is also investigated.

Tunable near-infrared emission of binary nano- and mesoscale GUMBOS

Mixtures of GUMBOS were used to form binary nanomaterials with tunable emission spectra due to Förster resonance energy transfer (FRET).

Photothermal response of near-infrared-absorbing NanoGUMBOS

The photothermal properties of several near-infrared-absorbing nanoparticles derived from group of uniform materials based on organic salts (GUMBOS) and composed of cationic dyes coupled with biocompatible anions are evaluated. These nanoparticles were synthesized using a reprecipitation method performed at various pH values: 2.0, 5.0, 7.0, 9.0, and 11.0. The cations for the nanoparticles derived from GUMBOS (nanoGUMBOS), [1048] and [1061], have absorbance maxima at wavelengths overlapping with human soft tissue absorbance minima. Near-infrared-absorbing nanoGUMBOS excited with a 1064 nm continuous laser led to heat generation, with an average temperature increase of 20.4 ± 2.7 °C. Although the [1061][Deoxycholate] nanoGUMBOS generated the highest temperature increase (23.7 ± 2.4 °C), it was the least photothermally efficient compound (13.0%) due to its relatively large energy band gap of 0.892 eV. The more photothermally efficient compound [1048][Ascorbate] (64.4%) had a smaller energy band gap of 0.861 eV and provided an average photothermal temperature increase of 21.0 ± 2.1 °C.