Emission enhancement of a carbazole-based fluorophore on a quantum dot surface.

A novel carbazole-based fluorophore 5-(carbazol-9-yl)-5'-mercapto-2,2'-bithiophene (CBTSH) was synthesized. CBTSH exhibited emission enhancement when attached to the surface of CdSe quantum dots (QDs). The emission quantum yield of CBTSH attached to CdSe is almost 5 times larger than that of CBTSH alone.

Mechanisms for the formation of acenes from α-diketones by bisdecarbonylation.

The bisdecarbonylation of bridged α-diketones has turned into an important reaction for the photochemical generation of higher acenes, in particular under matrix isolation conditions. Here, a computational mechanistic analysis of the bisdecarbonylation of dibenzobicyclo[2.2.

Sulfur containing stable unsubstituted heptacene analogs.

Heptacene and higher polyacenes have been sought for their high degree of charge carrier mobility in thin film transistors. Such acenes are, however, extremely unstable in ambient conditions. Approaches to obtain stable heptacenes include introduction of suitable substituents, of heteroatoms, or both.

Synthesis and photophysics of dibenz[a,c]phenazine derivatives.

The synthesis of dipolar dibenz[a,c]phenazine (DBP) derivatives is described. The compounds possess little electronic communication between donor and acceptor units in the ground state regardless of the pattern of substitution. The dipolar derivatives deactivate mostly via electron transfer (eT) under polar conditions.

Revisiting fluorenone photophysics via dipolar fluorenone derivatives.

The nonradiative decay of four dipolar fluorenone derivatives (FODs) was systematically investigated using steady state and time-resolved UV-vis absorption and fluorescence measurements combined with cyclic voltammetry. Analysis of the frontier orbital localization of the global minimum geometry and the vertical transitions was carried out from DFT calculations. The first singlet excited state was found to be π-π* in all derivatives regardless of the polarity of the solvent.

Nonradiative decay mechanism of fluoren-9-ylidene malononitrile ambipolar derivatives.

We report recent results on the nonradiative decay (NRD) of fluoren-9-ylidene malononitrile (FM) ambipolar derivatives (FMDs). 2,7- and 3,6-disubstituted FMDs present distinctive photophysics. Charge separation was found dominant for excited state relaxation.

Carbazole-based cyano-stilbene highly fluorescent microcrystals.

Aggregation-induced enhanced emission (AIEE) is reported for 1-cyano-trans-1,2-bis-(4-carbazolyl)phenylethylene (CN-CPE). The weak luminescence of dilute CN-CPE solutions is enhanced upon aggregate formation into 2-3 μm sized crystals. In contrast to general observations, crystal formation of CN-CPE causes a blue-shift in emission and enhances the intensity.

White light emission from co-precipitated organic nanoparticle composites.

Co-precipitation of 1,4-bis(2-phenyl-1-propen-1-yl)benzene (1) and 2-(4-(2-(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)ethynyl)benzylidene) malononitrile (2) that individually form blue-emitting and orange-emitting nanoparticles, respectively, results in the formation of composite fluorescent organic nanoparticles that emit white light. The two components likely align in the head-to-tail fashion in nanoparticles, creating two parallel and strongly coupled transition dipoles. The emission characteristics of the composite was dependent upon the concentration of 1 and 2, and a pure white-light emission (CIE chromaticity coordinates of 0.

Photopolymerization of conductive polymeric metal nanoparticles.

5-Mercapto-2,2'-bithiophene functionalized metal nanoparticles BTSMs [M: copper (Cu), silver (Ag), and gold (Au)] of different diameters (2-8 nm) were synthesized. Conductive polymeric metal nanoparticles were formed from BTSM by UV irradiation. The photopolymerization mechanism was investigated using transient absorption measurements.

Synthesis and photophysics of ambipolar fluoren-9-ylidene malononitrile derivatives.

The efficient synthesis of ambipolar 2,7- and 3,6-disubstituted fluoren-9-ylidene malononitrile derivatives (4 and 9) is described. Structure-activity relationships depend on the position of substitution. Population of the S(1) excited state in the 2,7-disubstituted FM derivatives is achieved via higher states, as evidenced from the UV-vis absorption and emission spectra.

Synthesis, stability, and photochemistry of pentacene, hexacene, and heptacene: a matrix isolation study.

The photochemical bisdecarbonylation of bridged alpha-diketones (Strating-Zwanenburg reaction) to give the oligoacenes pentacene (2), hexacene (3), and heptacene (4) is investigated in solid inert gas matrices at cryogenic temperatures. The photodecomposition using visible light irradiation cleanly produces the corresponding oligoacene without formation of observable intermediates. This synthetic approach to the higher acenes allows a comprehensive comparative study of their electronic absorption and infrared spectral properties under identical conditions for the first time.

Photophysical study of blue, green, and orange-red light-emitting carbazoles (1).

Simple synthetic procedures have been developed to prepare suitably substituted stable carbazoles B1-B3, G1-G3, and R1-R3. These compounds emit blue, green, and orange-red light, respectively, and show a red-shifted emission in the solid state relative to that in solution. The extent of the shift is highly dependent on the nature and the positions of the substituents.

Photoinduced hole transfer forming polymer quantum dot nanocomposites.

The study of hole transfer from CdSe QD core to ligands under visible light irradiation and conductive polymer-QD composites formation without conventional photoinitiator.

Photochemical synthesis of 2,3,9,10-tetrabromopentacene: its unusual photodimerization.

The photogeneration of 2,3,9,10-tetrabromopentacene from its precursor dione by photodecarbonylation was investigated. An unusual photodimer, 3,3',9,9',10,10'-hexabromo-2,2'-bipentacene, is produced.

Isomer restriction on a nanoparticle surface and enhanced blue emission.

5-Mercapto-2,2'-bithiophene (BTSH) functionalized copper (Cu), silver (Ag), and gold (Au) nanoparticles (NPs) of various diameters have been synthesized. Emission with a peak around 455 nm is detected on irradiation with UV light. This emission, however, disappears upon photopolymerization of the NPs.

Solvent dependent optical switching in carbazole-based fluorescent nanoparticles.

Suitably substituted ethynylphenyl carbazoles (PBM and PPM) form stable fluorescent organic nanoparticles. The emission of the nanoparticles can be reversibly switched on/off in the blue-green and orange-red regions by a change in the ratio of the tetrahydrofuran/water system used in their preparation. The size of the nanoparticles was found to be dependent on the solvent ratio, and the emissions were significantly red-shifted compared to those of dilute solutions of PBM and PPM in tetrahydrofuran.

Unusual photophysical properties of substituted carbazoles.

Photophysical properties of a new class of fluorescent, stable carbazoles (B1-B3, G1-G3, and R1-R2) as a function of excitation wavelength in matrixes and solution are reported. The emission maxima of B1 and B3 and G1-G3 show red shifts (6-16 nm) and substantially increased fluorescence quantum yields with a decrease in temperature from 25 to -10 degrees C. Considerable edge excitation red shift has been observed in B2.

Biocidal performance of acrylated glyphosate in a model photopolymerizable coating formulation.

Acrylated glyphosate was blended into a model polyolacrylate formulation and copolymerized. The resulting copolymer retains herbicidal activity similar to that of the monomer as indicated by the results of biological tests. No release of biocide from the coating was observed.

Gold nanoparticle photosensitized radical photopolymerization.

We report the photopolymerization of an acrylic monomer using thiol-stabilized gold nanoparticles (AuNPs) and [4-[(octyloxy)phenyl] phenyl] iodonium hexafluoroantimonate (OPPI) as photoinitiator and coinitiator, respectively. Polymerization occurred only when the AuNPs, in the presence of the iodonium salt, were irradiated at the particle plasmonic absorption region (lambda>450 nm). The AuNPs activate the coinitiator by intermolecular electron transfer since OPPI has no absorption in the visible region.

Photopolymerization of metal nanoparticles on multiwall carbon nanotubes.

A facile method for the functionalization of multiwall carbon nanotubes (MWCNT) by photopolymerization of 5-mercapto-2,2'-bithiophene modified metal (Au or Ag) nanoparticles on the surface of the MWCNT is developed.

Photochemical formation of substituted pentacenes.

Substituted pentacenes (8a, 8b, 14a, and 14b) were prepared by Strating-Zwanenburg photodecarbonylation of diones (7a, 7b, 13a, and 13b). The compounds are red and stable in the solid state under inert atmosphere as well as in degassed solutions, but not in air. Each is soluble in common organic solvents where, unless protected, they are oxygen sensitive.

Photochromic superabsorbent polymers.

Photochromic superabsorbent polymers (PSAPs) with a hydrophilic core and a photochromic shell were prepared by inverse suspension polymerization using acrylic acid (AA) and acrylamide (AM) as monomers, potassium persulfate as the initiator, N,N'-methylene bisacrylamide (BIS) as a cross-linker, sorbitan monostearate (Span60) as the dispersant, cyclohexane as the solvent and bis(methacryloylamino)azobenzene (AC) as the photochromic surface cross-linker. The polymer was characterized by NMR, infrared spectroscopy, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Water absorption (Q) and the photoresponse of the PSAPs was investigated.

Synthesis, characterization, and antifouling potential of functionalized copper nanoparticles.

The synthesis, characterization, and antimicrobial properties of functionalized copper nanoparticle/polymer composites are reported. Copper nanoparticles (Cu NPs) are stabilized by surface attachment of the acrylic functionality that can be copolymerized with other acrylic monomers, thus, becoming an integral part of the polymer backbone. Biological experiments show that Cu NP/polymer composites exhibit antimicrobial activity similar to that of conventional copper-based biocides.

Carbazole-based donor-acceptor compounds: highly fluorescent organic nanoparticles.

Carbazole-based donor-acceptor compounds 1,2-dicyano-trans-1,2-bis-4-(carbazolyl)phenylethylene (1) and 1,2-dicyano-trans-1,2-bis-4-(3,6-di-tert-butylcarbazolyl)phenylethylene (2) were synthesized. 1 and 2 show negative solvatochromic absorption behavior, but show both positive and negative solvatochromic behavior in the fluorescence spectra. In a water/THF mixture, 1 as well as 2 aggregate into 50-150 nm nanoparticles.

Photodecarbonylation of alpha-diketones: a mechanistic study of reactions leading to acenes.

Poly(acene)s are significant compounds for various electronic applications. A clean, one-step synthesis involves alpha-diketones (2-4), which undergo facile Strating-Zwanenburg photodecarbonylation producing the corresponding poly(acene)s (i.e.