We cap silver, copper, and gold nanocolloids with long-chain alkylxanthates. In comparison to thiol capping, the particles are less hydrophobic and are stable in aqueous solutions for over a month, though being less stable than the corresponding oleate-capped particles. They can be transferred into relatively polar organic media (such as dichloromethane) but not into nonpolar solvents (such as dodecane). Unlike noncapped, thiol-capped, and oleate-capped colloids, they are temperature sensitive, as a result of the thermal decomposition of the xanthate molecule itself, and can be applied as thermally decomposable colloids. They demonstrate exceptional resistivity toward cyanide-induced corrosion by oxygen, when compared to noncapped or even to oleate-capped colloids. Xanthate capping enables the production of stable copper nanocolloids in aqueous solution under ambient conditions.

We investigate the properties of long-chain alkyl xanthate-capped platinum nanoparticles. First an uncapped platinum colloid, 4.0 ± 1 nm in diameter, is produced in an aqueous phase, and then the capping agent is added. The capped particles are hydrophobic and easily transfer into organic solvents. They can be dried and repetitively transferred to various organic liquids in a reversible manner. Xanthate-capped platinum colloids are more stable than the analogous thiol-capped particles (and certainly noncapped particles) toward chemical corrosion (by oxygen in the presence of cyanide ion) and are also stable on heating. These colloids exhibit a characteristic sharp absorption in the range 450−470 nm in addition to the extinction in the UV. This absorption might be assigned tentatively to a weak d−d transition of platinum observed in this region also for the PtCl6 2- salt and for its adduct with xanthate, though it is absent for uncapped Pt particles. The transition for the capped colloid, however, is much stronger compared to that observed for the salts.

We study 2-(p-N-hexadecyl-N-methylamino)benzylidene-1,3-indandione (1a) as a model compound for the preparation of nonlinear optically (NLO) active Langmuir-Blodgett (LB) layers. The pressure-area (π-A) isotherm of (1a) at the air-water interface is investigated. A limiting area of 0.60 ( 0.02 nm 2 per molecule is found. The alternate-layer LB deposition of compound (1a) and an inert spacer, cadmium stearate, at different surface pressures is performed. The effects of temperature and delay time between spreading of the Langmuir film and the deposition of the LB films are studied. An increase of collapse pressure from 20 to 30 mN/m is observed as the delay time increases. UV-vis spectra indicate a uniform transfer of (1a) and show compressioninduced changes as a function of the deposition conditions. A split of the absorption maximum is observed for LB films deposited at higher pressures and lower temperatures. The two bands can result from two different molecular electronic transitions, affected by the aligning influence of the surface, and the different environments in the film compared to solution. Alternatively, these two bands can be associated with (at least) two different conformers. The orientation of the transition moments is evaluated on the basis of polarized UV-vis spectra at different angles of incidence, and found to be 40-44°. Significant second harmonic (SH) generation by the LB films is observed. Analysis of the SH response gives a tilt angle of 44°, in agreement with the finding from UV absorbance.

Quantum mechanical calculations show that N,N cycloaddition of alkenes and alkynes to s-tetrazines is possible as an alternative to the well-known C,C cycloaddition (Carboni-Lindsey reaction). Formation of 1,2,4-triazole derivatives (formal product of N,N cycloaddition) along with the pyrazole (formal product of C,C cycloaddition) corroborates this theoretical prediction.

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