Reversible intramolecular photocycloaddition of a bis(9-anthrylbutadienyl)paracyclophane--an inverse photochromic system. (Photoactive cyclophanes 5).

The title compound, 4,13-bis[(1E,3E)-4-(9-anthracenyl)buta-1,3-dienyl][2.2]paracyclophane (2), prepared in 35% overall yield from [2.2]paracyclophane, absorbs light at lambda(max) = 400 nm with a tail down to 480 nm. By irradiation into this band, 2 generates a single photoproduct, 4, whose absorption maximum is situated at 306 nm. The starting material is recovered by irradiation at 306 nm or by heating. This 'inverse' photochromic system has a potential for optical information storage, compound 4 being stable in visible light, at ambient temperature.

2,3-Diethoxy-9,10-anthraquinone.

Anthraquinone derivatives form an important class of dyes and are also known for their medicinal properties. Recently, 2,3-disubstituted anthraquinones have been shown unexpectedly to jellify various organic solvents. No information on the packing mode of these derivatives was known. Here, the first X-ray structure of a 2,3-disubstituted anthraquinone is reported, namely 2,3-diethoxy-9,10-anthraquinone, C(18)H(16)O(4). The merit of this study lies in the observation of significant differences between the packing in 9,10-anthraquinone, which displays a herring-bone arrangement, and that in the title 2,3-diethoxy derivative, in which the molecules lie on parallel crystallographic morror planes separated by a distance of 3.4081 (1) A, reminiscent of the graphite layer architecture.

Structural variations in a family of orthodialkoxyarenes organogelators.

A series of low mass organic gelators (LMOGS) 1 to 6 whose chemical structures have in common an orthodialkoxyarene feature was prepared in order to compare the shape of their fibrillar network as investigated by small-angle neutron scattering (SANS) experiments. All members of the family exhibit a pronounced tendency to bundle formation by merging isolated fibers in extended packets of average diameter >500 A. Variations of the 2D packing symmetry are observed from hexagonal to square orderings with close derivatives of the reference member 2,3-didecyloxyanthracene (DDOA). Networks in which the fraction of isolated fibers is significant enough to allow for their SANS identification are those for 6,7-dichloro-2,3-didecyloxyanthracene (Cl(2)DDOA) and 2,3-dodecyloxy-9,10-anthraquinone (5). For this latter, the monodispersity of the cross-sections (thickness=74 A) is remarkable and the rectangular shape (b/a approximately 0.12) accounts for a merging mechanism into anisotropic bundles (ribbons).

Synthesis of 2,3-substituted tetracenes and evaluation of their self-assembling properties in organic solvents.

[structure: see text] Rod-shaped 2,3-di-alkoxytetracenes, soluble in common organic solvents, have been synthesized and studied for their gelling ability in organic solvents and their unusual UV-visible spectroscopic properties.

Photodimers of a soluble tetracene derivative. excimer fluorescence from the head-to-head isomer.

[reaction: see text] Irradiation of 5,12-didecyloxytetracene (1) leads to photodimers P(1) (planosymmetric) and P(2) (centrosymmetric). P(1) is characterized by naphthalene excimer fluorescence, whereas P(2) emits naphthalene monomer fluorescence.

Photoprotodesilylation of 9-trimethylsilylanthracene in alcohols.

It was found that the anomalous fluorescence quenching in methanol (as compared to other solvents) of 9-trimethylsilylanthracene (2) is accompanied by a chemical reaction leading to anthracene. This ipso substitution is due to a hydrogen bonding formation in the excited singlet state preceding the carbon-silicon bond cleavage. The mechanism was studied using stationary and dynamic fluorescence, laser flash photolysis and reactivity kinetics as a function of temperature. The kinetic parameters were determined for the formation of an intermediate "X" (A(X) approximately 2.5 x 10(11) s(-1) Ea(X) approximately 19.5 kJ mol(-1)) and for the global reaction (A(R) approximately 4 x 10(10) s(-1) and Ea(R) approximately 19.2 kJ mol(-1)), indicating that, after the formation of X, the reaction does not involve any step with an activation energy larger than 19 kJ mol(-1). The intermediate X undergoes partitioning between the product (a approximately 0.18) and the starting material. The isotopic effect for the quenching by methanol was found to be kX(H)/kX(D) approximately 1.9, in keeping with the proposed protonation in the excited singlet state (S1). The reactivity ratio between the S1 state and the ground state, kR(S1)/ kR(S0) approximately 10(12) is in line with those observed by other authors. This unusual photoreaction can proceed for 2 with other alcohols. ipsoProtodesilylation of aromatic silanes are known to occur in the ground state but in acidic media.

Factors predicting long-term efficacy of Hylan GF-20 viscosupplementation in knee osteoarthritis.

OBJECTIVES: To describe the long-term effects of Hylan GF-20 viscosupplementation in patients with knee osteoarthritis and to identify factors predicting efficacy. METHODS: One hundred and fifty-five patients (80 women and 75 men; mean age, 69 years) with symptomatic knee osteoarthritis each received three intraarticular Hylan GF-20 injections. Effectiveness, safety, and satisfaction were evaluated 7-14 months later based on a physician's examination and a five-item questionnaire. Radiological data (distribution and degree of joint space loss), size of the effusion (none, moderate, large), injection route (anterior, medial to the patella, or lateral to the patellar), and side effects were recorded. Factors predicting effectiveness were looked for by univariate analysis followed by multivariable analysis with adjustments on age, body mass index, gender, and time from treatment to questionnaire administration. RESULTS: Satisfaction was good in 78% and 58.9% of the patients according to the physician examination and questionnaire, respectively. Safety was considered excellent or good in 96.2% of the patients. Factors significantly (P < 0.05) associated with a good outcome were a moderate effusion, injection lateral to the patella, joint space loss in a single compartment, and radiological meniscal calcinosis. CONCLUSION: The factors predictive of a good response to Hylan GF-20 in this study need to be confirmed, and their impact quantitated, in prospective studies.

Photoinduced formation of a cryptand from a coronand: an unexpected switch in cation binding affinity.

Aza-crown ethers 2 and 3 with anthracene-containing pendant arms have been synthesised and characterised. Both compounds bind Group 1 metal cations in solution, forming complexes of 1:1 stoichiometry. The properties of compound 2 and its complexes have been studied by a range of techniques, including NMR, UV and fluorescence spectroscopy and X-ray crystallography. The pendant arms can adopt either a cis or a trans geometry, the cis geometry favoured with larger cations. The geometry of the complex affects the fluorescence properties of the system, with larger cations giving higher excimer/monomer ratios. Upon irradiation at lambda>300 nm, coronand 2 forms the cryptand 5 through a reversible intramolecular [4pi+4pi] cycloaddition reaction. The rates of the forward and reverse reactions of this photochromic process are cation dependent; in particular the rate of the thermal reverse reaction is decreased by smaller cations and increased by larger cations, especially Rb(+). The metal binding constants in methanol for 2 and 5 have been determined, revealing that the cryptand 5 binds Na(+) and Rb(+) more weakly than crown ether 2 by over two orders of magnitude.

Bis(isoquinoline N-oxide) pincers as a new type of metal cation dual channel fluorosensor.

[structure: see text] A new type of donor-spacer-acceptor podand system has been synthesized and proved as an efficient dual channel fluorosensor for Li+, Mg2+, and Ca2+. The known ability for the N-oxide function to bind Lewis acids is the key step in the appearance of a new emitting charge-transfer (CT) excited state. The occurrence of this CT state for alkaline earth (Mg2+ and Ca2+) and not for alkaline metals (Li+) provided a new type of dual channel fluorosensors.