Michael B. Sponsler

Switchable holograms recorded in liquid crystalline monomers

Holographic gratings recorded by photopolymerization of liquid crystalline monomers have been immediately and reversibly developed, or switched, by application of electric fields. Diffraction efficiency modulation has exceeded 200-fold, with maximum efficiency about 13% in the on state for 10 micrometers samples. Fixing of the holograms in the more efficient state has been accomplished by short exposure to a single writing beam. Microscopic images of the switching gratings recorded on videotape have provided information about grating structure and supported our proposed mechanism for the recording and switching effects.

Iodine-induced transannular coupling of 1,6-cyclodecadiyne

Treatment of 1,6-cyclodecadiyne (1) with one equivalent of iodine in ether leads to regioselective transannular coupling, producing 1,5-diiodo-2,3,4,6,7,8-hexahydronaphthalene (2) in excellent yield. Solvent-incorporation products are observed in addition to 2 when the reaction is done in benzene, chlorobenzene, or methanol. Bromination of 1 gives analogous products, but the reaction is not as clean.

Synthesis and X-ray structural determination of pentamethylcyclopentadienyl dichloro oxo molybdenum

Abstract Dark red crystals of the paramagnetic complex Cp*MoCl 2 (O) (Cp*=η 5 −C 5 (CH 3 ) 5 ) were obtained from the reaction of Cp*MoCl 4 and water. The compound crystallizes in the triclinic space group P 1 with a =8.654(2), b = 11.150(3), c =6.545(1) A, α= 93.76(3), β = 91.12(3), γ= 85.68(3)°, V = 628.3(3) A 3 , D calc =l.681 g/cm 3 and Z =2. The structure was solved and refined based on 1463 reflections with F o ⩾6σ( F o ) (6104 collected; Mo Kα radiation, λ=0.71073 ») and R =0.033. The piano-stool structure, exhibiting a distorted Cp* ligand, is compared with reported structures for the closely related compounds, CpMoCI 2 (O) (Cp=η 5 −C 5 H 5 ), Cp*VCl 2 (O) and Cp*ReCl 2 (O).

Trithiocarbonate-mediated free-radical photopolymerization: improved uniformity in hologram recording.

A holographic material based on a photopolymerizable nematic acrylate was improved by the addition of the trithiocarbonate, EtO2CCH2SC(S)SCH2CO2Et, increasing uniformity and reproducibility in the formation of electrically switchable holographic gratings. Diffraction efficiencies as high as 34%, the thin-grating theoretical maximum, were achieved at large (10-14 microm) grating spacings. Improved diffraction efficiency was seen over a range of grating spacings (0.35-10 microm). The exposure window for grating formation was increased by an order of magnitude, resulting in much improved reproducibility.

Liquid crystalline monomers as switchable holographic recording media

Abstract Dynamic holographic gratings have been recorded by photopolymerization of a liquid crystalline monomer mixture. Clean on- off modulation of diffraction efficiency has been achieved by application and removal of small (3 V) AC electric fields. The samples showed high efficiency, sensitivity, and switching durability. An optional fixing step was also demonstrated.