Search results for "Effects"
showing 10 items of 2634 documents
Weak intermolecular interactions promote blue luminescence of protonated 2,2′-dipyridylamine salts
2014
In this work we demonstrate that protonation and π-stacking can be exploited to convert non-luminescent 2,2′-dipyridylamine into blue-emitting derivatives. We have synthesized a series of luminescent 2,2′-dipyridylamine (dpa) salts, i.e., (dpaH)X·nSolv (dpa = 2,2′-dipyridylamine, X = HF2, n = 0.5, Solv = H2O 1; X = Cl, n = 2, Solv = H2O 2; X = Br, n = 2, Solv = H2O 3; X = I n = 1, Solv = H2O 4a; X = I n = 1, Solv = CHCl34b), (dpaH)2[SiF6]·H2O 5 and (dpaH)X (X = I36; SbF67; BF48) and characterized their emission properties, both in the solid-state and in solution. To rationalize our observations and relate the luminescence properties to the structure in the solid state and in solution, we ha…
Effect of self-assembled surfactant structures on ion transport across the liquid|liquid interface
1999
In this paper, the effect of a coadsorbed polyanion–cationic surfactant system on the transport of tetraethylammonium ion across the water|1,2-dichloroethane interface is studied. It is shown that the change in double-layer structure due to the presence of adsorbed or coadsorbed surfactant can explain the experimental observations, thus concluding that no other effects on ion transfer (e.g., steric hindrance) are relevant under these experimental conditions. The implications of these results are discussed. Keywords: ITIES, Ion transfer, Self-assembled monolayers, Surfactants, Double-layer effects
Chemistry of density : extension and structural origin of Carnelley's rule in chloroethanes
2012
Low-density liquids and solids, with all intermolecular contacts longer than the sum of van der Waals radii, are formed by all ethanes chlorinated at one locant: CH2ClCH3, CHCl2CH3 and CCl3CH3. The concepts of molecular symmetry described by Carnelley and that of point groups have been compared. Carnelley's rule, when applied to liquid and solid chloroethanes clearly reveals the density dependence on the presence of intermolecular Cl⋯Cl and H⋯Cl short contacts, or their absence due to steric hindrances of overcrowded substituents. At 2.62 GPa, CH2ClCH3 freezes directly into phase II, with molecules arranged into layers with short Cl⋯Cl, H⋯Cl and H⋯H contacts. Only for CH2ClCH3, both the low…
Solid State Luminescence Enhancement in π-Conjugated Materials: Unraveling the Mechanism beyond the Framework of AIE/AIEE
2017
Solid state luminescence enhancement (SLE) of conjugated organic materials has had a great impact in materials science, but a deep understanding has been rather limited to date. Here, we investigate a prototype example of SLE materials, cyano-substituted distyrylbenzene (DCS), by varying systematically and subtly the substitution pattern (inter alia of the position of the cyano-substituent) to give largely different photoresponse in fluid and solid solution as well in the crystalline state. The combination of quantitative (ultra)fast optical spectroscopic techniques, appropriate quantum-chemical methods, and structural (X-ray) data allows us to elucidate and rationalize all details of the S…
Rare-earth metal bis(tetramethylaluminate) complexes supported by a sterically crowded triazenido ligand
2010
Complexes [NNN]Ln(AlMe(4))(2) (Ln = Y, La, Nd, Lu) bearing the sterically demanding aryl-substituted triazenido ligand [(Tph)(2)N(3)] (Tph = [2-(2,4,6-iPr(3)C(6)H(2))C(6)H(4)]) can be obtained from homoleptic complexes Ln(AlMe(4))(3) in moderate yields, both via protonolysis with [(Tph)(2)N(3)]H and a salt metathesis reaction pathway utilizing [(Tph)(2)N(3)]K. In the solid state the Y and Lu derivatives are isostructural, with both tetramethylaluminate groups coordinated in an eta(2) fashion, while one of the [AlMe(4)] ligands of the Nd derivative features a distorted eta(2) coordination mode. Due to the high affinity of the triazenido ligand toward the more Lewis-acidic and harder aluminiu…
Highly Conjugatedp-Quinonoidπ-Extended Tetrathiafulvalene Derivatives: A Class of Highly Distorted Electron Donors
2004
A new class of pi-extended TTF-type electron donors (11 a-c) has been synthesized by Wittig-Horner olefination of bianthrone (9) with 1,3-dithiole phosphonate esters (10 a-c). In cyclic voltammetry experiments, donors 11 a-c reveal a single, electrochemically irreversible oxidation-yielding the corresponding dicationic products-at relatively low oxidation potentials (approximately 0.7-0.8 V). Theoretical calculations, performed at the DFT level (B3 P86/6-31 G*), predict a highly-folded C(2h) structure for 11 a. In the ground state, the molecule adopts a double saddle-like conformation to compensate the steric hindrance. The calculations suggest that the intramolecular charge transfer associ…
Micelles formed from photochemically active amphiphiles: structural characterization by small-angle neutron scattering
1996
Abstract A novel class of photochemically active amphiphiles has been synthesized containing a ketone moiety as a biradical or radical pair precursor on the hydrophobic tail of sodium sulfate surfactants. Alteration of the molecular structure of each ketone-containing surfactant allows for the systematic and predictable manipulation of the micellar size and shape, both of which are important in determining the coupling between the unpaired electrons confined within the micelle and the intraradical dynamics. The structure of the resulting aggregates has been analyzed by small-angle neutron scattering (SANS). The results show that the amphiphiles form ellipsoidal micelles with aggregation num…
(o-Hydroxyphenyl)methylphosphonic acids: Synthesis and potentiometric determinations of their pKaValues
1993
(o-Hydroxyphenyl)methylphosphonic acids are readily obtained from o-(bromomethyl)- or o-(hydroxymethyl)phenols and trialkyl phosphites. Subsequent hydrolysis leads to the corresponding phosphonic acids. For a series of such compounds, the pKa values have been determined by potentiometry. Their dependence on additional substituents in the aromatic ring is discussed in terms of electronic and steric effects.
Thermotropic properties and molecular packing of discotic tristriazolotriazines with rigid substituents.
2014
Tristriazolotriazines with a threefold dialkoxyaryl substitution have been prepared by Huisgen reaction of cyanuric chloride and the corresponding tetrazoles. Although these dyes show a negative or inverted solvatochromism of the UV/Vis absorption, their fluorescence is strongly positive solvatochromic. These discotic fluorophores are also emissive in their solid state and in their broad liquid-crystalline mesophase. The structural study indicates that the thermotropic properties and organization of these systems can be well tuned by the steric demand of the aryl groups. Depending on the substituents, the compounds showed either a pure crystalline phase or a highly complex helical superstru…
On the reaction of 3-bromo-2-nitrobenzo[b]thiophene with some ortho-substituted anilines: an analysis of the products of reaction and of their NMR an…
2003
Abstract The title reaction, carried out in DMF in the presence of triethylamine or potassium carbonate, has furnished the ‘expected’ 3-amino-2-nitrobenzo[ b ]thiophenes 2 o together with the ‘unexpected’ 2-amino-3-nitrobenzo[ b ]thiophenes 3 o , thus recalling the situation observed with other weak nucleophiles in the presence of non-nucleophilic bases. The effects (electronic as well as steric) of the ortho -substituent (OH, NH 2 , OMe, Me, Et, F, Cl and Br) on the course of the reaction have been investigated, determining their influence on yields and product ratios ( 2 o / 3 o ). An analysis of 13 C NMR and MS spectra of 2 o and 3 o has been carried out. Ab initio computations on 2 o f …