Long Range Electronic Effects on the Host-Guest Complexation within the Oxygen Depleted 5,5'-Bicalixarene Cavities.

We report the synthesis of a series of the oxygen-depleted conjugated 5,5'-Bicalix[4]arene compounds bearing various substituents at the terminal positions of the conjugated chain and their fluorescence response to the presence of a cationic N-methylpyridinium guest. The complexation of this cation within the bicalixarene cavity results in the fluorescence quenching, with the host molecules bearing electron-donating groups demonstrating a stronger fluorescence response. These results show the importance of the electronic effects on the host-guest complexation within the hydrophobic calixarene scaffolds.

Carbazole-fused calixarene cavities: single and mixed AIEgen systems for NO detection.

Novel oxygen-depleted calix[4]arenes containing fused carbazole moieties demonstrate AIEgen behavior in aqueous solutions. This phenomenon leads to highly sensitive detection of nitric-oxide guest molecules because it affects intra- and intermolecular energy transfer within aggregates.

Fluorophore-Appendant 5,5'-Bicalixarene Scaffolds for Host-Guest Sensing of Nitric Oxide.

Conjugated 5,5'-Bicalixarene scaffolds having fluorophores at the chain termini have been prepared and tested in the supramolecular detection of nitric oxide. Scaffolds bearing electron-rich fluorophores demonstrated a stronger turn-off response to the presence of NO than the fluorophore-free analogue in both organic and aqueous media, while no fluorescence quenching happened when the electron-deficient fluorophores were employed. Unprecedented ratiometric supramolecular sensing was observed when fluorophores of the opposite electronic demands were placed at the scaffold's termini.

Selective detection of chemical warfare agents VX and Sarin by the short wavelength inner filter technique (SWIFT).

A novel SWIFT-based strategy for fluorimetric detection of practical amounts (minimal effective dose or lower) of chemical warfare agents is reported. This strategy employs readily available reagents and allows distinguishing between the V and G agents, as well as their discrimination from potential interferents.

Short Wavelength Inner Filter Technique (SWIFT) in Designing Reactive Fluorescent Molecular Probes.

Here, we present a conceptually novel and experimentally straightforward technique for selective analyte detection that uses a combination of commercial fluorophores and simple chemicals. The technique utilizes the well-known inner filter effect (IFE); however, the fluorophore's excitation is performed at wavelengths significantly shorter than its absorption maximum. In the presence of the analyte, the "filter" appears or disappears at the excitation wavelength resulting in the fluorescence turning OFF or ON, respectively. Unlike common probes, our technique allows real-time monitoring of a fluorophore's stability as well as its recycling. We further demonstrate the applicability of this technique in continuing analyte detection as well as vapor analysis.

Fluorene-based sensitizers with a phenothiazine donor: effect of mode of donor tethering on the performance of dye-sensitized solar cells.

Two types of fluorene-based organic dyes featuring T-shape/rod-shape molecular configuration with phenothiazine donor and cyanoacrylic acid acceptor have been synthesized and characterized as sensitizers for dye-sensitized solar cells. Phenothiazine is functionalized at either nitrogen (N10) or carbon (C3) to obtain T-shape and rod-like organic dyes, respectively. The effect of structural alternation on the optical, electrochemical, and the photovoltaic properties is investigated. The crystal structure determination of the dye containing phenyl linker revealed cofacial slip-stack columnar packing of the molecules. The trends in the optical properties of the dyes are interpreted using time-dependent density functional theory (TDDFT) computations. The rod-shaped dyes exhibited longer wavelength absorption and low oxidation potentials when compared to the corresponding T-shaped dyes attributable to the favorable electronic overlap between the phenothiazine unit and the rest of the molecule in the former dyes. However, the T-shaped dyes showed better photovoltaic properties due to the lowest unoccupied molecular orbital (LUMO) energy level favorable for electron injection into the conduction band of TiO2 and appropriate orientation of the phenothiazine unit rendering effective surface blocking to suppress the recombination of electrons between the electrolyte I3(-) and TiO2. The electrochemical impedance spectroscopy investigations provide further support for the variations in the electron injection and transfer kinetics due to the structural modifications.

N-(4,4'-Dibromo-[1,1'-biphen-yl]-2-yl)benzamide.

In the title compound, C(19)H(13)Br(2)NO, the dihedral angle between the rings of the biphenyl group is 53.59 (14)°. The ring of the benzamide group is inclined to the phenyl rings of the biphenyl group by 23.87 (15) and 75.89 (15)°. There are no significant inter-molecular inter-actions in the crystal structure.

Fine tuning the performance of DSSCs by variation of the π-spacers in organic dyes that contain a 2,7-diaminofluorene donor.

Organic dyes that contain a 2,7-diaminofluorene-based donor, a cyanoacrylic-acid acceptor, and various aromatic conjugation segments, which are composed of benzene, fluorene, carbazole, and thiophene units, as a π-bridge have been synthesized and characterized by optical, electrochemical, and theoretical investigations. The trends in the absorption and electrochemical properties of these dyes are in accordance with the electron-donating ability of the conjugating segment. Consequently, the dyes that contained a 2,7-carbazole unit in the π-spacer exhibited red-shifted absorption and lower oxidation potentials than their corresponding fluorene- and phenylene-bridged dyes. However, the enhanced power-conversion efficiency that was exhibited by the fluorene-bridged dyes in the DSSCs was attributed to their broader and intense absorption. Despite the longer-wavelength absorption and reasonable optical density, carbazole-bridged dyes exhibited lower power-conversion efficiencies, which were ascribed to the poor alignment of the LUMO level in these dyes, thereby leading to the inhibition of electron injection into the TiO(2) conduction band.

N-(7-Bromo-9-butyl-9H-carbazol-2-yl)-9,9-diethyl-N,N,N-triphenyl-9H-fluorene-2,7-diamine.

In the title mol-ecule, C(51)H(46)BrN(3), the central fluorene residue is planar (r.m.s. deviation = 0.0203 Å), as is the carbazole system (r.m.s. deviation = 0.0154 Å), and these groups are almost orthogonal [dihedral angle = 79.72 (3)°]. The three-dimensional architecture is consolidated by C-H⋯π inter-actions. The butyl substituent is disordered with two sites resolved for the terminal propyl atoms; the major component had a site-occupancy factor of 0.686 (3).

Pyrene-based organic dyes with thiophene containing π-linkers for dye-sensitized solar cells: optical, electrochemical and theoretical investigations.

A new series of metal-free organic dyes containing pyrene and α-cyanoacrylic acid end groups and thiophene, bithiophene, thienylbenzene or thienylfluorene π-linkers were synthesized and characterized by absorption, emission and electrochemical measurements. Time-dependent density functional theoretical calculations were also performed to unravel the nature of the absorption induced electronic excitations. Extension of conjugation in the π-linker by the incorporation of phenyl or fluorene was found to enhance the molar extinction coefficient while the use of thiophene red-shifted the absorption. The longer wavelength absorption peaks found for the dyes were attributed to π-π* transition with a contribution from the charge transfer transition which becomes prominent for the bithiophene bridged derivative. The bithiophene containing dye showed moderate overall light-to-electron conversion efficiency attributable to the favorable absorption and redox properties originating due to the presence of a bithiophene segment. The trends observed for the various dyes in the device performance were rationalized by electron-impedance spectroscopy measurements.

Synthesis and optical properties of acidochromic amine-substituted benzo[a]phenazines.

A new series of alkylamine- or arylamine-substituted benzo[a]phenazines have been synthesized from 1,2-naphthoquinones by employing simple sequential Michael-type addition with a variety of primary and secondary amines and the condensation reaction of the resulting amine-substituted 1,2-naphthoquinones with o-phenylenediamine. They exhibited absorption peaks originating from the charge transfer transition between the amine and pyrazine segments and benzo[a]phenazine localized π-π* transitions. Although the absorption spectra of the dyes were not significantly influenced by the nature of the solvents, addition of TFA led to a prominent red-shift in the absorption spectra owing to the protonation at the quinoxaline segment which enhanced the electron-accepting ability. The qualitative trends observed in the optical properties and acidochromism were supported by density functional theoretical computations. The dyes displayed positive solvatochromism in the emission spectra suggestive of a more polar excited state. The dyes were also characterized by a quasi-reversible reduction couple originating from the pyrazine segment which underwent shifts corresponding to electron-donating strength of the amine segment.

2,7-Diaminofluorene-based organic dyes for dye-sensitized solar cells: effect of auxiliary donor on optical and electrochemical properties.

New organic dyes containing a diarylaminofluorene unit as an electron donor and cyanoacrylic acid as acceptor and anchoring group in a donor-π-donor-π-acceptor architecture have been synthesized and characterized as sensitizers for nanocrystalline TiO(2)-based dye-sensitized solar cells. They have shown three major electronic absorptions originating from the π-π* and charge-transfer transitions covering the broad visible range (250-550 nm) in solution. The charge-transfer transition of the dyes exhibited negative solvatochromism, suggesting a polarized ground state. They have also displayed acidochromism in solution owing to the presence of a protonation-deprotonation equilibrium. On comparison with the triphenylamine and carbazole-based parent dyes (E)-2-cyano-3-(4-(diphenylamino)phenyl)acrylic acid and (E)-2-cyano-3-(9-ethyl-9H-carbazol-3-yl)acrylic acid they exhibited longer wavelength absorptions and facile oxidation, indicating the stronger electron-donating ability of the auxiliary chromophores. In addition, they exhibited nearly two times larger light-to-electron conversion efficiency under simulated AM 1.5 G irradiation (100 mW cm(-2)) with an aperture mask when compared to the parent dyes. Among the new dyes, the one containing the naphthylphenylamine segment showed better device characteristics attributable to the higher HOMO energy level which probably facilitates the regeneration of the dye and effective suppression of the back reaction of the injected electrons with the I(3)(-) in the electrolyte. The optical properties of the dyes were modeled using TDDFT simulations employing different theoretical models (B3LYP, CAM-B3LYP, and MPW1K), and the best correlations with the observed parameters have been found for CAM-B3LYP and MPW1K calculations. The electron lifetimes extracted from the electrochemical impedance measurements of the dye-sensitized solar cells were used to interpret the solar cell efficiency alternations.