Real-time multiplexed digital cavity-enhanced spectroscopy.

Cavity-enhanced spectroscopy is a sensitive optical absorption technique but one where the practical applications have been limited to studying small wavelength ranges. This Letter shows that wideband operation can be achieved by combining techniques usually reserved for the communications community with that of cavity-enhanced spectroscopy, producing a multiplexed real-time cavity-enhanced spectrometer. We use multiple collinear laser sources operating asynchronously and simultaneously while being detected on a single photodetector. This is synonymous with radio frequency (RF) cellular systems in which signals are detected on a single antenna but decoded uniquely. Here, we demonstrate results with spectra of methyl salicylate and show parts-per-billion per root hertz sensitivity measured in real-time.

A highly symmetric diamond-like assembly of cyclotricatechylene-based tetrahedral cages.

The combination of six Cu(II) centres with four cyclotricatechylene (ctc(6-)) ligands generates large (Cu(6)ctc(4))(12-) cages with the topology of the tetrahedron. The anionic tetrahedral cages are cemented together, triangular face to triangular face, by Na(+) cations together with water molecules to generate a highly symmetric diamond-like assembly (space group Fd-3m, the same as that of diamond itself) whose adamantane-like units have an iodide ion at the centre of every cyclohexane-like face.

A doughnut-like (Mn(III))12 metallocycle formed by a rigid angular bis-catecholate with a nanometer-sized central hole.

Reaction of the rigid angular ligand tetrahydroxy-9,10-dimethyl-9,10-dihydro-9,10-ethanoanthracene, hereafter LH(4), with Mn(CH(3)CO(2))(2) x 2 H(2)O in a basic aqueous medium, in air, affords a crystalline product of composition Na(12){[Mn(H(2)O)](12)L(12)} x xH(2)O. Single-crystal X-ray diffraction reveals the presence of large [Mn(III)(12)L(12)](12-) metallocycles of roughly hexagonal appearance, somewhat resembling a doughnut in which the central hole (van der Waals surface to surface) is roughly a nanometer across. This is the first example of a metal derivative of the fully deprotonated form, L(4-). Associations with aquated Na(+) counterions lead to a pleasingly symmetrical packing arrangement resembling honeycomb, with the central holes of individual metallocycles lined up one above the other. The ligand L(4-), on account of its rigid angularity and its strong metal binding properties, promises to provide a rich source of unusual metal-containing structures, in particular cages, in future studies.

Cages with tetrahedron-like topology formed from the combination of cyclotricatechylene ligands with metal cations.

Cage the elephant: anionic tetrahedral assemblies, formed from the combination of cyclotricatechylene anions with transition metal ions, such as vanadium, contain large internal cavities that can act as hosts for alkali metal ions and solvent molecules. With appropriate metal centers, the anionic units can be linked together to form highly symmetric coordination polymers (V blue, O red, C black).

Closed and open clamlike structures formed by hydrogen-bonded pairs of cyclotricatechylene anions that contain cationic "meat".

Clamming up: The hexaphenolic compound cyclotricatechylene, which has a bowl-shaped cavity, forms clamlike pairs that encapsulate cations (see picture). Variable hydrogen bonding allows two linked cyclotricatechylene clamshells to be in a closed arrangement when smaller cations such Rb(+) or Cs(+) provide the clam meat, whereas larger cations such as NMe(4) (+) and NEt(4) (+) cause the clam to be partially opened.