Toward Fluorescence-Based High-Throughput Screening for Enantiomeric Excess in Amines and Amino Acid Derivatives.

A highly accurate and reliable screening method for enantiomeric excess of amine derivatives in the presence of water is reported. The fluorescence-based screening system has been realized by self-assembly of chiral diol-type dyes (BINOL, VANOL and VAPOL), 2-formylphenylboronic acid, and chiral amines forming iminoboronate esters. The structure and chirality of the amine analytes determine the stability of the diastereomeric iminoboronate esters, which in turn display differential fluorescence. The fluorescence signal reflects the enantiomeric purity of the chiral amines and was utilized in high-throughput arrays. The arrays were able to recognize enantiomeric excess of amines, amino esters, and amino alcohols. In addition to qualitative analysis, quantitative experiments were successfully performed. Studies of the role of additives such as water or citrate were carried out to gain insight into the stability of the iminoboronate esters. It is shown that the above additives destabilize less stable esters while the stable esters remain unchanged. Thus, the presence of water and citrate leads to increased difference between the diastereomeric iminoboronates and contributes to the enantiodiscrimination of the chiral amines.

Low power threshold photochemical upconversion using a zirconium(iv) LMCT photosensitizer.

The current investigation demonstrates highly efficient photochemical upconversion (UC) where a long-lived Zr(iv) ligand-to-metal charge transfer (LMCT) complex serves as a triplet photosensitizer in concert with well-established 9,10-diphenylanthracene (DPA) along with newly conceived DPA-carbazole based acceptors/annihilators in THF solutions. The initial dynamic triplet-triplet energy transfer (TTET) processes (ΔG ∼ -0.19 eV) featured very large Stern-Volmer quenching constants (K SV) approaching or achieving 105 M-1 with bimolecular rate constants between 2 and 3 × 108 M-1 s-1 as ascertained using static and transient spectroscopic techniques. Both the TTET and subsequent triplet-triplet annihilation (TTA) processes were verified and throughly investigated using transient absorption spectroscopy. The Stern-Volmer metrics support 95% quenching of the Zr(iv) photosensitizer using modest concentrations (0.25 mM) of the various acceptor/annihilators, where no aggregation took place between any of the chromophores in THF. Each of the upconverting formulations operated with continuous-wave linear incident power dependence (λ ex = 514.5 nm) down to ultralow excitation power densities under optimized experimental conditions. Impressive record-setting η UC values ranging from 31.7% to 42.7% were achieved under excitation conditions (13 mW cm-2) below that of solar flux integrated across the Zr(iv) photosensitizer's absorption band (26.7 mW cm-2). This study illustrates the importance of supporting the continued development and discovery of molecular-based triplet photosensitizers based on earth-abundant metals.

Controlling Thermally Activated Delayed Photoluminescence in CdSe Quantum Dots through Triplet Acceptor Surface Coverage.

Quantum-dot/molecule composites (QD/mol) have demonstrated useful photochemical properties for many photonic and optoelectronic applications; however, a comprehensive understanding of these materials remains elusive. This work introduces a series of cadmium(II) selenide/1-pyrenecarboxylic acid (CdSe/PCA) nanomaterials featuring bespoke PCA surface coverage on CdSe585 (coded by the peak of the first exciton absorption band) to glean insight into the QD/mol photophysical behavior. Tailoring the energy gap between the CdSe585 first exciton band (2.1 eV) and the lowest PCA triplet level (T1 = 2.0 eV) to be nearly isoenergetic, strong thermally activated delayed photoluminescence (TADPL) is observed resulting from reverse triplet-triplet energy transfer. The resultant average decay time constant (τobs) of the photoluminescence emanating from CdSe585 is deterministically controlled with surface-bound PCAn chromophores (n = average number of adsorbed PCA molecules) by shifting the triplet excited state equilibrium from the CdSe585 to the PCA molecular triplet reservoir as a function of n.

Accessing the triplet manifold of naphthalene benzimidazole-phenanthroline in rhenium(I) bichromophores.

The steady-state and ultrafast to supra-nanosecond excited state dynamics of fac-[Re(NBI-phen)(CO)3(L)](PF6) (NBI-phen = 16H-benzo[4',5']isoquinolino[2',1':1,2]imidazo[4,5-f][1,10]phenanthrolin-16-one) as well as their respective models of the general molecular formula [Re(phen)(CO)3(L)](PF6) (L = PPh3 and CH3CN) has been investigated using transient absorption and time-gated photoluminescence spectroscopy. The NBI-phen containing molecules exhibited enhanced visible light absorption with respect to their models and a rapid formation (<6 ns) of the triplet ligand-centred (LC) excited state of the organic ligand, NBI-phen. These triplet states exhibit an extended excited state lifetime that enable the energized molecules to readily engage in triplet-triplet annihilation photochemistry.

Exploiting fluorescent zinc(ii) and copper(ii) complexes for enantiomeric excess determination of hydroxycarboxylates.

Chiral hydroxycarboxylates are useful compounds in the syntheses of natural products, pharmaceutical intermediates, and drugs. Here, we report on Zn- and Cu-containing sensors that can distinguish between enantiomers of hydroxycarboxylates through the quenching or the enhancement of fluorescence. A Zn-based sensor-[ZnRRL]2+-is used in an assay to perform analyses of enantiomeric excess (% ee) of scalemic mixtures of α-hydroxycarboxylates and various drugs including the statin drug atorvastatin. This assay enables determination of mixtures of enantiomers across the range from 0 to 100% ee.

An indicator displacement assay recognizes enantiomers of chiral carboxylates.

Two chiral copper(ii)-based receptors-[CuRRL]2+ and [CuSSL]2+-in conjuction with the fluorescent indicator coumarin 343 were used to establish an enantioselective indicator displacement assay (eIDA) for the determination of the enantiomeric composition of chiral carboxylates such as ibuprofen, naproxen and atorvastatin.

Toward wearable sensors: optical sensor for detection of ammonium nitrate-based explosives, ANFO and ANNM.

Increasing security needs require compact and portable detection tools for the rapid and reliable identification of explosives used in improvised explosive devices (IEDs). We report of an easy-to-use optical sensor for both vapour-phase and solution-phase identification of explosive mixtures that uses a cross-reactive fluorimetric sensor array comprising chemically responsive fluorimetric indicators composed of aromatic aldehydes and polyethyleneimine. Ammonium nitrate-nitromethane (ANNM) was analyzed by paper microzone arrays and nanofiber sensor mats. Progress toward wearable sensors based on electrospun nanofiber mats is outlined.

Fluorescent zinc and copper complexes for detection of adrafinil in paper-based microfluidic devices.

Recognition of electroneutral Lewis bases and anions in aqueous media is extremely difficult. We show that fluorescent coordinatively unsaturated metal complexes can recognize various Lewis bases while providing an easy-to-detect fluorescence response. This approach is applied to the detection of adrafinil, a banned performance-enhancing drug.