Search results for "PHOTOCHEMISTRY"
showing 10 items of 2034 documents
Do the Intramolecular π Interactions Improve the Stability of Ionic, Pyridine-Carbene-Based Iridium(III) Complexes?
2013
Throughout the last years one of the most intensive research topics in light-emitting electrochemical cells (LECs) focused on the design of blue-emitting, ionic iridium(III) complexes. To this end, the most recent strategy is the use of carbene-based ancillary ligands. Although blue LECs have been successfully fabricated, the stability has been noted as the main drawback. To overcome this problem, Zhang et al. have recently explored the use of π interactions to enhance the strength of pyridine-carbene-based complexes. The authors suggested that the use of intramolecular π–π stacking interactions by means of pendant phenyl rings to improve the stability of LECs is not as effective as in devi…
Soluble oligo(phenylenevinylene)s with electron withdrawing substituents for the use in light emitting diodes
2000
Poly(p-phenylenevinylene) (PPV) and its derivatives are one of the most widely used classes of phosphors in light emitting diodes. Central problems are the imbalanced charge carrier injection and transport properties due to the high lying conduction band. A series of good soluble oligo(phenylenevinylene)s (OPV) with five benzene rings and a variety of electron withdrawing and accepting substituents have been prepared and may serve as model compounds for PPV with increased electron affinity. The central ring of the OPVs is substituted with two octyloxy groups to ensure good solubility and the lateral styrene units carry further chromophoric groups of different electronic character. The synth…
Redox switching of the antiferromagnetic coupling in permethylated dicopper(ii) paracyclophanes
2012
A unique magnetic electroswitching behavior has been observed in an oxamato-based permethylated dicopper(II) paracyclophane; upon reversible one-electron oxidation of the double tetramethyl-substituted p-phenylenediamidate bridging skeleton, the spin alignment of the two Cu(II) ions (S(Cu) = ½) changes from antiparallel (OFF) to parallel (ON) in the resulting dicopper(II) π-radical cation species.
Mass spectra of chlorinated aromatics formed in pulp bleaching: I—chlorinated catechols
1983
The fragmentation of chlorinated guaiacols (2-methoxyphenols) on electron impact has been studied. The most common fragmentation processes are interpreted and in some cases the small differences between spectra of positional isomers are explained. In addition to the well-known alkyl-oxygen fission (loss of methyl radical), metastable ion studies and deuterium labelling have indicated several new fragmentation pathways. The most characteristic are the formation of [MCH3HCl]+ and [MCH3Cl]+· ions. In general, however, the spectra of positional isomers are shown to be very similar.
Radical cations and dications of bis[1]benzothieno[1,4]thiazine isomers
2021
Bis[1]benzothieno[1,4]thiazines (BBTT) are particularly electron-rich S,N-heteropentacenes and their radical cations and dications can be relevant intermediates in charge transport materials. All three regioisomers of N-p-fluorophenyl-BBTT (syn–syn, syn–anti, and anti–anti) were studied. A reliable preparation of radical cations and dications using antimony pentachloride as an oxidant gives deeply colored salts. The electronic structure of the radical cations was assessed by EPR spectroscopy, whereas dicationic structures were characterized by NMR spectroscopy. In addition, a deeper insight into the electronic structure was experimentally and computationally obtained by UV/Vis spectroscopy …
Methylium Ions with OPV Chains − New NIR Dyes
2001
Carbinols, which contain three OPV chains, were generated in convergent syntheses. The extension of the conjugation leads to a bathochromic effect that shifts the absorption from the UV into the visible region. The carbinol series has a convergence limit of the absorption at λmax = 415 nm. The corresponding carbenium ions exhibit a stronger bathochromic shift with the increasing number of repeating units in each chain. Thus, NIR dyes were obtained which show a convergence limit at λmax = 879 nm. The charge distribution in the ground state of the carbocations is discussed on the basis of 13C NMR spectroscopic data.
Areno-Condensed 1,7,13-Triaza[18]annulenes
2002
The 1,7,13-triaza[18]annulenes 9a−c were prepared by multi-step processes in which the final step consisted of a threefold cyclic condensation reaction of the Schiff bases 8a−c. Due to the length of the nine peripheral alkoxy chains, discotic liquid crystalline phases were obtained for 9b,c. The three nitrogen atoms in the central 18-membered ring not only permit protonation, but they can also serve for the complexation of NH4+ ions. The compounds 9a−c are highly photosensitive and exhibit crosslinking reactions on irradiation.
Arylethynyl-Substituted Tristriazolotriazines: Synthesis, Optical Properties, and Thermotropic Behavior
2014
The synthesis of C3-symmetrical tristriazolotriazines with conjugated arms and lateral alkoxy side chains was performed by a threefold condensation of cyanuric chloride with tetrazoles. Conjugated π segments include phenyl, tolane, and its phenylethynyl-elongated homologue. Disclike and a dendritic molecule have been obtained, and two compounds with a 3,4,5-tris(octyloxy) substitution form broad thermotropic mesophases. The linear optical properties, solvatochromism of the fluorescence, acidochromism, and the two-photon absorption efficiency of selected compounds are reported.
Extension of Conjugation Leading to Bathochromic or Hypsochromic Effects in OPV Series
2004
Four OPV series 1-4 (a-d) with a terminal dialkylamino group as electron donor were prepared by Wittig-Horner reactions. To study the influence of the push-pull effect on the long-wavelength absorption, three of the four series contained terminal acceptor groups (CN, CHO, NO(2)). The length of the chromophores strongly affects the intramolecular charge transfer (ICT)-an effect which superimposes upon the extension of the conjugation. Increasing numbers n of repeat units cause an overall bathochromic shift for the purely donor-substituted series 1 a-4 a and the series 1 b-4 b with CN as weak acceptor. The two effects annihilate each other in the series 1 c-4 c with terminal CHO groups, so th…
A DFT study of the mechanism of Brønsted acid catalysed Povarov reactions
2015
Abstract The molecular mechanism of the Bronsted acid (BA) catalysed Povarov reaction of N -phenyl- C -methoxycarbonyl imine with a methylenecyclopropane (MCP) has been investigated using DFT methods at the MPWB1K/6-31G(d) level. This BA catalysed Povarov reaction is a domino process initialised by the formation of a cationic intermediate which experiences a quick intramolecular Friedel–Crafts reaction yielding the final tetrahydroquinoline. Protonation of the imine nitrogen atom notably increases the electrophilicity of the corresponding species, accelerating the reaction through ionic processes. Analysis of the Parr functions in the initial nucleophilic attack of MCP to the protonated imi…