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A novel fluorescent host-guest material, molecular sieves of AlPO4-5-type doped with 2,2'-bipyridyl-3,3'-diol, was prepared and spectroscopically characterized. The composite crystals show a pronounced optical anisotropy, indicating a high degree of alignment of the guest molecules within the zeolitic pore system. A mean tilting angle of 22 was found for the orientation of the individual dye molecules in the straight channels. The corrected fluorescence emission spectra were determined, and time-resolved fluorescence studies revealed that the dye molecules are preferentially found in three different types of microenvironment. By invoking pH-dependent studies of the dye in aqueous solution, we could trace these spectroscopic features back to two main influences, coadsorbed water within AlPO4-5 pores and guest-host interactions with a few relatively weak Brnsted acid (defect) sites of the inorganic host network.
A series of twelve 3-piperazinyl propenylidene indolone merocyanines was synthesized in a one-pot fashion using a consecutive three-component insertion-coupling-Michael addition sequence. Physicalorganic treatment of the absorption data of a consanguineous series of this library allows semiquantitative Linear Free Energy Relationships (LFERs) to be established and confirmation of the positive Absorption solvatochromicity. All Boc-substituted piperazinyl merocyanines display aggregation induced Emission (AIE), which was corroborated for two solvent systems. In particular, crystallization-induced Emission enhancement (CIEE) induced by ultrasonication could be shown for a model chromophore by confocal laser scanning microscopy (CLSM).
Bright, long-lived emission from first-row transition-metal complexes is very challenging to achieve. Herein, we present a new strategy relying on the rational tuning of energy levels. With the aid of the large N-Cr-N bite angle of the tridentate ligand ddpd (N,N′-dimethyl-N,N′-dipyridine-2-ylpyridine-2,6-diamine) and its strong σ-donating capabilities, a very large ligand-field splitting could be introduced in the chromium(III) complex [Cr(ddpd)2]3+, that shifts the deactivating and photoreactive 4T2 state well above the emitting 2E state. Prevention of back-intersystem crossing from the 2E to the 4T2 state enables exceptionally high near-infrared phosphorescence quantum yields and lifetimes for this 3d metal complex. The complex [Cr(ddpd)2](BF4)3 is highly water-soluble and very stable towards thermal and photo-induced substitution reactions and can be used for fluorescence intensity- and lifetime-based oxygen sensing in the NIR.
Quaternary ammonium compounds (QACs) are widely used as active agents in disinfectants, antiseptics, and preservatives. Despite being in use since the 1940s, there remain multiple open questions regarding their detailed mode-of-action and the mechanisms, including phenotypic heterogeneity, that can make bacteria less susceptible to QACs. To facilitate studies on resistance mechanisms towards QACs, we synthesized a fluorescent quaternary ammonium compound, namely N-dodecyl-N,N-dimethyl-[2-[(4-nitro-2,1,3-benzoxadiazol-7-yl)amino]ethyl]azanium-iodide (NBD-DDA). NBD-DDA is readily detected by flow cytometry and fluorescence microscopy with standard GFP/FITC-settings, making it suitable for molecular and single-cell studies. As a proof-of-concept, NBD-DDA was then used to investigate resistance mechanisms which can be heterogeneous among individual bacterial cells. Our results reveal that the antimicrobial activity of NBD-DDA against Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa is comparable to that of benzalkonium chloride (BAC), a widely used QAC, and benzyl-dimethyl-dodecylammonium chloride (BAC12), a mono-constituent BAC with alkyl-chain length of 12 and high structural similarity to NBD-DDA. Characteristic time-kill kinetics and increased tolerance of a BAC tolerant E. coli strain against NBD-DDA suggest that the mode of action of NBD-DDA is similar to that of BAC. As revealed by confocal laser scanning microscopy (CLSM), NBD-DDA is preferentially localized to the cell envelope of E. coli, which is a primary target of BAC and other QACs. Leveraging these findings and NBD-DDA‘s fluorescent properties, we show that reduced cellular accumulation is responsible for the evolved BAC tolerance in the BAC tolerant E. coli strain and that NBD-DDA is subject to efflux mediated by TolC. Overall, NBD-DDA’s antimicrobial activity, its fluorescent properties, and its ease of detection render it a powerful tool to study resistance mechanisms of QACs in bacteria and highlight its potential to gain detailed insights into its mode-of-action.
Lanthanide-doped upconversion nanoparticles (UCNPs) are of great interest for biomedical applications. Currently, the applicability of UCNP bionanotechnology is hampered by the generally low luminescence intensity of UCNPs and inefficient energy Transfer from UCNPs to surface-bound chromophores used e.g. for photodynamic therapy or analyte sensing. In this work, we address the low-Efficiency issue by developing versatile core-Shell nanostructures, where high-concentration sensitizers and activators are confined in the core and Shell Region of representative hexagonal NaYF2:Yb,Er UCNPs. After Doping concentration optimization, the sensitizer-rich core is able to harvest/accumulate more excitation energy and generate almost one order of Magnitude higher luminescence intesity than conventional homogeneously doped nanostructures. At the same time, the activator Ions located in the Shell enable a ~6 times more efficient resonant energy Transfer from UCNPs to surface-bound acceptor dye molecules due to the short distance between donor-acceptor pairs. Our work provides new insights into the rational design of UCNPs and will greatly encrease the General applicability of upconversion nanotechnologies.
Organic/inorganic mixtures were prepared from ordinary Portland cement (OPC), water (w/c 0.22), a fluorescent dye in aqueous solution (stable at alkaline pH; BAM-I), and two different comb shape polycarboxylates (PCEs), i.e., high charge (PCE-HC) and low charge (PCE-LC), respectively. Rheological and calorimetric measurements were performed prior to optical studies in order to select PCE concentrations. Absorption and fluorescence spectroscopy of the system OPC + BAM-I (CBAM-I) revealed maxima of dye BAM-I located at 645 nm and 663 nm, respectively. In presence of PCE-HC and PCE-LC, these mixtures displayed a small red shift in reflectance and a faster decrease in intensity compared to studies with CBAM-I; however, only slight differences were observed between the different PCEs. With time, all systems exhibited a decrease in intensity of BAM-I in absorption/reflectance and emission. This could be caused by dye adsorption and possibly decomposition when in contact with cement particles or hydration products.
Organic/inorganic mixtures were prepared from ordinary Portland cement (OPC), water (w/c 0.22), a fluorescent dye in aqueous solution (stable at alkaline pH; BAM-I), and two different comb shape polycarboxylates (PCEs), i.e., high charge (PCE-HC) and low charge (PCE-LC), respectively. Rheological and calorimetric measurements were performed prior to optical studies in order to select PCE concentrations. Absorption and fluorescence spectroscopy of the system OPC + BAM-I (CBAM-I) revealed maxima of dye BAM-I located at 645 nm and 663 nm, respectively. In presence of PCE-HC and PCE-LC, these mixtures displayed a small red shift in reflectance and a faster decrease in intensity compared to studies with CBAM-I; however, only slight differences were observed between the different PCEs. With time, all systems exhibited a decrease in intensity of BAM-I in absorption/reflectance and emission. This could be caused by dye adsorption and possibly decomposition when in contact with cement particles or hydration products.
The synthesis, structure, reactivity,and photophysical properties of anovel acidic,luminescentchromium(III) complex [Cr(H2tpda)2]3+ (23+ +)bearing the tridentate H2tpda (2,6-bis(2-pyridylamino)pyridine) ligand are presented. Excitation of 23+ + at 442 nm results in strong, long-lived NIR luminescence at 782 nm in water and in acetonitrile. X-ray diffraction analysis and IR spectroscopy revealhydrogen-bonding interactions of the counter ions to the NH groups of 23+ + in the solidstate. Deprotonation of the NH groups of 23+ + by using anon-nucleophilic Schwesinger base in CH3CN switches off the luminescence. Re-protonation by using HClO4 restores the emission. In water,the pKa value of 23+ + amountsto8 .8, yet deprotonation is not reversible in the presence of hydroxide ions. Dioxygen quenches the emission of 23+ +,but to aweaker extent than expected. This is possibly due to the strong ion-pairing properties of 23+ + even in solution, reducing the energy transfer efficiency to O2.Deuteration of the NH groups of 23+ + approximately doubles the quantum yield and lifetime in water,demonstrating the importance of multiphoton relaxation in these NIR emitters.