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A highly fluorescent pH sensing membrane for the alkaline pH range incorporating a BODIPY dye
(2013)
A robust and re-usable dipstick-type fluorescent pH sensor for the alkaline pH range was developed by embedding a brightly fluorescent borondipyrromethene (BODIPY) dye bearing an acidic phenol moiety into a polyurethane matrix immobilized on a 3D epoxy-functionalized polymer support. The sensor strip has a dynamic working range of pH 10.0–13.1, i.e., operates in strongly basic media where pH glass electrodes can suffer from alkaline errors, and tolerates a high electrolyte background such as simulated seawater and sewage. This work describes the preparation of the sensing material and provides insight into the features that a hydrogel sensing membrane can bestow on an embedded pH-responsive dye by means of optical spectroscopic investigations.
Fluorinated Boron-Dipyrromethene (BODIPY) dyes: bright and versatile probes for surface analysis
(2013)
A family of bright boron-dipyrromethene-type fluorophores with a high number of fluorine atoms (F-BODIPYs) has been developed and characterized by X-ray crystallography and optical spectroscopy. The introduction of 3,5-bis(trifluoromethyl)phenyl and pentafluorophenyl moieties significantly enhances the photostability of such dyes, yielding for instance photostable near-infrared (NIR) fluorophores that show emission maxima>750 nm, when the BODIPY's π system is extended with two (dimethylamino)styryl and (dimethylamino)naphthastyryl moieties, or green-emitting BODIPYs with fluorescence quantum yields of unity. When equipped with a suitable group that selectively reacts for instance with amines, F-BODIPYs can be used as potent dual labels for the quantification of primary amino groups on surfaces by X-ray photoelectron spectroscopy (XPS) and fluorescence, two powerful yet complementary tools for the analysis of organic surface functional groups. The advantage of reactive F-BODIPYs is that they allow a fast and non-destructive mapping of the labelled supports with conventional fluorescence scanners and a subsequent quantification of selected areas of the same sample by the potentially traceable XPS technique. The performance is exemplarily shown here for the assessment of the amino group density on SiO2 supports, one of the most common reactive silica supports, in particular, for standard microarray applications.
A family of N-crowned 4-p-(aminophenyl)-2,6-diphenylpyridines DA (1-6) has been synthezised, characterized, and studied as potential hosts for the signaling of cationic and anionic guests. The ditopic probes contain two coordination sites, a monodentate 2,6-diphenylpyridine and an anilino group with macrocycles of different ring size, denticity, and type of secondary heteroatom (O and/or S). X-ray structure analysis of aza-oxa-thia-crowned 5 indicated a largely planar chromophore. Optical spectroscopic and electrochemical studies revealed that the anilino-type donor (D) and the 2,6-diphenylpyridine acceptor (A) are strongly -conjugated, entailing intense intramolecular charge-transfer absorption bands at 340 nm. Binding studies with protons and metal ions (M = Cu2+, Zn2+, Hg2+, Fe3+, Pb2+, Ni2+, Cd2+) showed shifts of the band to the visible (440 nm) when coordination at the pyridine group occurs, strengthening its acceptor character. In contrast, no band in the visible is formed if binding takes place at the anilino group. Three different responses were found for various pairs of DA and M: selective metal coordination to D or A as well as coordination at both sites. A selective response was found for 5 and Hg2+. Because of the multitude of coordination-induced effects, the DA-M ensembles were further employed for differential anion sensing. In this protocol, the addition of an anion X to a certain, weakly coordinated DA-M can (i) lead to the formation of a ternary ion pair complex (DA-M-X), (ii) change the preference for A or D coordination, (iii) induce dissociation of the complex, or (iv) can have no effect. Various patterns of absorption changes were obtained as a result of different responses (i)-(iv) of the DA-M's in the presence of various X's. Data analysis yielded recognition patterns for acetate, F- and CN-, demonstrating the potential of simple chromogenic host-guest pairs for differential anion signaling.
The X-ray crystallographic, optical spectroscopic, and electrochemical properties of a newly synthesized class of boron-diindomethene (BDI) dyes and their tetrahydrobicyclo precursors (bc-BDP) are presented. The BDI chromophore was designed to show intensive absorption and strong fluorescence in an applicationary advantageous spectral range. Its modular architecture permits fusion of a second subunit, for example, a receptor moiety to the dye's core to yield directly linked yet perpendicularly prearranged composite systems. The synthesis was developed to allow facile tuning of the chromophore platform and to thus adjust its redox properties. X-ray analysis revealed a pronounced planarity of the chromophore in the case of the BDIs, which led to a remarkable close packing in the crystal of the simplest derivative. On the other hand, deviation from planarity was found for the diester-substituted bc-BDP benzocrown that exhibits a butterfly-like conformation in the crystal. Both families of dyes show charge- or electron-transfer-type fluorescence-quenching characteristics in polar solvents when equipped with a strong donor in the meso-position of the core. These processes can be utilized for signaling purposes if an appropriate receptor is introduced. Further modification of the chromophore can invoke such a guest-responsive intramolecular quenching process, also for receptor groups of low electron density, for example, benzocrowns. In addition to the design of various prototype molecules, a promising fluoroionophore for Na+ was obtained that absorbs and emits in the 650 nm region and shows a strong fluorescence enhancement upon analyte binding. Furthermore, investigation of the remarkable solvatokinetic fluorescence properties of the butterfly-like bc-BDP derivatives suggested that a second intrinsic nonradiative deactivation channel can play a role in the photophysics of boron-dipyrromethene dyes.
Set them free: Brightly fluorescent indicators that are loaded into mesoporous silica nanoparticle carriers, capped with bulky antibodies, are released into the lateral flow of a test strip upon analyte arrival. Integration of the system into a rapid, simple flow test with fluorescence readout is applied for the selective and sensitive determination of the presence of triacetone triperoxide (TATP) as a prototype small-molecule analyte (see figure).
Four azulene dyads have been synthesized and studied by spectroscopic and electrochemical methods. A triarylamine, a boron-dipyrromethene (BDP or BODIPY), a porphyrin, and an isoalloxazine moiety have been linked to an extended π electron system at the 2-position of azulene, leading to the dyads 1–4, respectively. For the synthesis of 1–4, first 2-(4-ethynyl-phenyl)azulene (EPA) was prepared, which was further reacted with the halogenated chromophores by Pd-catalyzed cross-coupling reactions. The dyads 1–4 exhibit strong absorption bands in the visible range, which are dominated by the absorption spectra of the individual subchromophores. Fluorometric studies of 2–4 revealed that after excitation of the subchromophoric unit attached to the parent azulene moiety, quenching mainly through energy transfer to azulene is effective, whereas possible charge-transfer interactions play only a minor role. Potentiodynamic oxidation of the dyads 1–4 leads to the formation of polymer films, which are deposited at the electrode. The polymer film derived from 1 was further characterized by spectroelectrochemistry. During positive doping of poly-1, a strong absorption band appears at 13,200 cm1, which is typical for triarylamine radical cations. This band is overlapping with a broad absorption band in the low-energy region that might be caused by charge-transfer interactions within the polymer.
Fluorescence quantum yields of a series of red and near-infrared dyes emitting at 600-1000 nm
(2011)
The determination of the fluorescence quantum yields (QY, Φf) of a series of fluorescent dyes that span the absorption/excitation and emission ranges of 520-900 and 600-1000 nm is reported. The dyes encompass commercially available rhodamine 101 (Rh-101, Φf = 0.913), cresyl violet (0.578), oxazine 170 (0.579), oxazine 1 (0.141), cryptocyanine (0.012), HITCI (0.283), IR-125 (0.132), IR-140 (0.167), and four noncommercial cyanine dyes with specific spectroscopic features, all of them in dilute ethanol solution. The QYs have been measured relative to the National Institute of Standards and Technology's standard reference material (SRM) 936a (quinine sulfate, QS) on a traceably characterized fluorometer, employing a chain of transfer standard dyes that include coumarin 102 (Φf = 0.764), coumarin 153 (0.544), and DCM (0.435) as links between QS and Rh-101. The QY of Rh-101 has also been verified in direct measurements against QS using two approaches that rely only on instrument correction. In addition, the effects of temperature and the presence of oxygen on the fluorescence quantum yield of Rh-101 have been assessed.