Polysiloxane coatings containing chemically-bound ("tethered") quaternary ammonium salt (QAS) moieties were investigated for potential application as environmental-friendly coatings to control marine biofouling. A combinatorial/high-throughput approach was applied to the investigation to enable multiple variables to be probed simultaneously and efficiently. The variables investigated for the moisture-curable coatings included QAS composition, ie alkyl chain length, and concentration as well as silanol-terminated polysiloxane molecular weight. A total of 75 compositionally unique coatings were prepared and characterized using surface characterization techniques and biological assays. Biological assays were based on two different marine microorganisms, a bacterium, Cellulophaga lytica and a diatom, Navicula incerta, as well as a macrofouling alga, Ulva. The results of the study showed that all three variables influenced coating surface properties as well as antifouling (AF) and fouling-release (FR) characteristics. The incorporation of QAS moieties into a polysiloxane matrix generally resulted in an increase in coating surface hydrophobicity. Characterization of coating surface morphology revealed a heterogeneous, two-phase morphology for many of the coatings investigated. A correlation was found between water contact angle and coating surface roughness, with the contact angle increasing with increasing surface roughness. Coatings based on the QAS moiety containing the longest alkyl chain (18 carbons) displayed the highest micro-roughness and, thus, the most hydrophobic surfaces. With regard to AF and FR properties, coatings based on the 18 carbon QAS moieties were very effective at inhibiting C. lytica biofilm formation and enabling easy removal of Ulva sporelings (young plants) while coatings based on the 14 carbon QAS moities were very effective at inhibiting biofilm growth of N. incerta.

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Silicon nanocrystals (SiNCs) with bright bandgap photoluminescence (PL) are of current interest for a range of potential applications, from solar windows to biomedical contrast agents. Here, we use the liquid precursor cyclohexasilane (Si6H12) for the plasma synthesis of colloidal SiNCs with exemplary core emission. Through size separation executed in an oxygen-shielded environment, we achieve PL quantum yields (QYs) approaching 70% while exposing intrinsic constraints on efficient core emission from smaller SiNCs. Time-resolved PL spectra of these fractions in response to femtosecond pulsed excitation reveal a zero-phonon radiative channel that anticorrelates with QY, which we model using advanced computational methods applied to a 2 nm SiNC. Our results offer additional insight into the photophysical interplay of the nanocrystal surface, quasi-direct recombination, and efficient SiNC core PL.

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141 Crystal structure analysis of (Et4N),. 7 . C H X N (the values in brackets represent results of a structure determination on a second data set obtained from an independently grown new crystal): a = 16.557(!) [16.563(4)], b = 18.915(6) [18.879(6)], C = 17.110(6) [17.108(5)] A, a = / f = y = 9 0 " ; space group, Pbcm, 2 = 4 , pCalcd=1.35 g cm-,, pl,hu,= 1.40 g cm-,, p=12.9 cm-', 2Q,,,=4O0 (MoKa, L=O.71069A); 2620 unique reflections; used in refinement with F~z > 3 u ( F~) : 1290 [1376]; parameters 198. Final R=0.0699 I0.07331, R, =0.0647 10.06891. The low number of observed reflections for both data sets is due to the fact that crystals of high crystallographic quality could not be isolated. This problem, coupled with positional disorders encountered with two of the three [Et4N]" cations, accounts for the rather high temperature factors obtained for some of the carbon atoms. Further details of the crystal structure investigation are available on request from the Fachinformationszentrum Energie, Physik, Mathematik GmbH, D-7514 Eggenstein-Leopoldshafen 2 (FRG), on quoting the depository number CSD-53 196, the names of the authors, and the journal citation. [IS] H. Beinert, A. Dedicated to Professor Hans Bock on the occasion of his 60th birthdayAlthough the chemistry of the silanediyls is well developed and of continuing interest,"] there are few convenient methods for generating these species on a preparative scale. We had need for a variety of methods for making di-rert-butylsilanediyl (2) and in this communication we report three convenient routes for generating this intermediate, possibly in a complexed form like 8, in high yields.'21 2 has been proposed as a product of the photolyses of hexa-tert-butylcy~lotrisilane~~~ and di-tert-butylsilyldi-a~i d e . '~] We have found [Eqn. (a)] that when di-tert-butyl-dichlorosilane ( l a ) and lithium in T H F in the presence of excess of triethylsilane, were irradiated with ultrasonic waves using an ultrasonic cleaning bath, the di-tert-butylsilanediyl insertion product l,l,l-triethyl-2,2-di-tert-butyldisilane (3) was isolated in 60% yield.[51 The same product was obtained in comparable yields from l b and l c . This is the first example of a metal-promoted a-elimination of dihalosilanes on a preparative scale. tBu2SiX2 + Li a [tBu,Si:] E13S'H * Et,Si-SiHtBu2 (a) l a , X = C1 2 Ib, X = Br lc, x = 1 3We have investigated the reactions of l a and lithium with other trapping agents and in the absence of a quenching agent. With trans-butene for example, 1,l-di-tert-butyltrans-2,3-dimethylsilirane (4), was isolated in 65-70% yield. None of the cis isomer was detected by gas chromatography. When cis-butene was used as a trap, 1,l-di-tertbutyl-cis-2,3-dimethylsilirane was also isolated in 65-70% yield.16] A small amount (< 5%) of 4 was detected along with 5 but was understood to arise from the presence of 2-5% trans-butene in our samples of cis-butene.