Nanoscale plasmonic stamp lithography on silicon.

Nanoscale lithography on silicon is of interest for applications ranging from computer chip design to tissue interfacing. Block copolymer-based self-assembly, also called directed self-assembly (DSA) within the semiconductor industry, can produce a variety of complex nanopatterns on silicon, but these polymeric films typically require transformation into functional materials. Here we demonstrate how gold nanopatterns, produced via block copolymer self-assembly, can be incorporated into an optically transparent flexible PDMS stamp, termed a plasmonic stamp, and used to directly functionalize silicon surfaces on a sub-100 nm scale.

UV-initiated hydrosilylation on hydrogen-terminated silicon (111): rate coefficient increase of two orders of magnitude in the presence of aromatic electron acceptors.

UV-initiated (254 nm) hydrosilylation of hexadecene on Si(111)-H has been studied in the presence of various aliphatic and aromatic molecules (additives). Many of these additives cause an enhancement in the pseudo-first-order rate coefficient (k(obs)) of hydrosilylation, some up to 200× faster than observed in neat hexadecene. It is proposed that these additives capture the photoejected electron from the surface, thereby increasing the probability of reaction of the alkene with the surface hole (h(+)), leading to Si-C bond formation.

Toward a mechanistic understanding of exciton-mediated hydrosilylation on nanocrystalline silicon.

White-light initiated hydrosilylation of nanocrystalline porous silicon was found to be far more efficient (in terms of both kinetics and yield) in the presence of electron-accepting molecules with suitably high reduction potentials, particularly halocarbons. It is known that absorption of visible light by nanocrystalline silicon results in the formation of excitons (electron/hole pairs) and that this exciton can be harnessed to drive a hydrosilylation reaction with an alkene; the Si-C bond forms as a result of attack of the π-electrons of the alkene on the positively charged holes. In order to better understand the white-light initiated mechanism through which this reaction takes place, and to compare with UV-mediated photoemission on Si(111)-H, a series of electron acceptors were screened for their effect on surface alkene hydrosilylation.

A glimpse at the chemistry of GeH2 in solution. Direct detection of an intramolecular germylene-alkene π-complex.

The photochemistry of 3-methyl-4-phenyl-1-germacyclopent-3-ene (4) and a deuterium-labeled derivative (4-d(2)) has been studied in solution by steady state and laser flash photolysis methods, with the goal of detecting the parent germylene (GeH(2)) directly and studying its reactivity in solution. Photolysis of 4 in C(6)D(12) containing acetic acid (AcOH) or methanol (MeOH) affords 2-methyl-3-phenyl-1,3-butadiene (6) and the O-H insertion products ROGeH(3) (R = Me or Ac) in yields of ca. 60% and 15-30%, respectively, along with numerous minor products which the deuterium-labeling studies suggest are mainly derived from hydrogermylation processes involving GeH(2) and diene 6.

Long-range intramolecular photoredox reaction via coupled charge and proton transfer of triplet excited anthraquinones mediated by water.

The formal intramolecular photoredox reaction initially discovered for the parent 2-(hydroxymethyl)anthraquinone (1) has been extended to include analogs 3-6 in which the oxidizable benzyl alcohol group is significantly further away from the anthraquinone moiety. All of 3-6 undergo a clean and efficient formal intramolecular photoredox reaction in water catalyzed by acid (Phi = 0.1-0.

1,1-Bis[4-(trifluoro-meth-yl)phen-yl]germetane.

The inter-nal C-Ge-C bond angle in the germacyclo-butane ring of the title compound, C(17)H(14)F(6)Ge or [Ge(C(3)H(6))(C(7)H(4)F(3))(2)], is 77.8 (3)°. The -CF(3) groups display rotational disorder [occupancies 0.

Photoaddition of water and alcohols to the anthracene moiety of 9-(2'-hydroxyphenyl)anthracene via formal excited state intramolecular proton transfer.

The title compound undergoes efficient photoaddition of a molecule of a hydroxylic solvent (H(2)O, MeOH, (Me)(2)CHOH) across the 9- and 10-positions of the anthracene moiety to give isolable triphenylmethanol or triphenylmethyl ether type products. The reaction is believed to proceed via a mechanism involving water-mediated formal excited state intramolecular proton transfer (ESIPT) from the phenolic OH to the 10-position of the anthracene ring, generating an o-quinone methide intermediate that is observable by nanosecond laser flash photolysis, and is trappable with nucleophiles. A "water-relay" mechanism for proton transfer seems plausible but cannot be proven directly with the data available.

Photochemical deuterium exchange of the m-methyl group of 3-methylbenzophenone and 3-methylacetophenone in acidic D2O.

Photolysis of the title compounds in acidic aqueous solution results in "activation" of the distal m-methyl group, resulting in deuterium exchange (Phi approximately 0.1) when D(2)O is used. The reaction is not observed in neutral aqueous solution or in deuterated organic solvents such as CD(3)CN.