Single electron transfer-promoted photocyclization reactions of linked acceptor-polydonor systems: effects of chain length and type on the efficiencies of macrocyclic ring-forming photoreactions of tethered alpha-silyl ether phthalimide substrates.

Results of an investigation, aimed at gaining information about the factors governing the efficiencies of single electron transfer (SET)-promoted photocyclization reactions of linked acceptor-polydonor systems, are described. One set of substrates used in this effort includes alpha-trimethylsilyl ether terminated, polymethylene- and polyethylenoxy-tethered phthalimides and 2,3-naphthalimides. Photocyclization reactions of the polyethylenoxy-linked phthalimides and naphthalimides were observed to take place in higher chemical yields and with larger quantum efficiencies than those of analogs containing polymethylene tethers of near equal length. These findings show that the rates of formation of 1,omega-zwitterionic biradicals that serve as key intermediates in the photocyclization processes are enhanced in substances that contain oxygen donor sites in the chain. The findings suggest that these donor sites facilitate both initial SET to acceptor excited states and ensuing intrachain SET, resulting in migration of the cation radical center to the terminal alpha-trimethylsilyl ether position. In addition, an inverse relationship was observed between the quantum yields of photocyclization reactions of the tethered phthalimides and naphthalimides and the length of the polyethylenoxy chain. Finally, the roles played by chain type and length in governing photoreaction efficiencies were investigated by using intramolecular competition in photoreactions of polyethylenoxy and polymethylene bis-tethered phthalimides. Mechanistic interpretations and synthetic consequences of the observations made in this study are discussed.

Relationship between crystal packing and high electron mobility in the single crystal of thienyl-substituted methanofullerene.

The X-ray crystal structure of 1-(3-methoxy-carbonyl)-propyl-1-thienyl-[6,6]-methanofullerene (ThCBM) was determined and the electron mobility of the single crystal was measured using a TRMC method to reveal high electron mobility (2 cm(2) V(-1) s(-1)) along the long axis (a-axis) and its remarkable anisotropy (7 times).

Photoaddition reactions of 1,2-diketones with silyl ketene acetals. formation of beta-hydroxy-gamma-ketoesters.

Photochemical reactions taking place between 1,2-diketones and silyl ketene acetals and their excited state reaction mechanisms have been explored. Irradiation of benzene, acetone, or acetonitrile solutions containing 1,2-diketones and silyl ketene acetals is observed to promote formation of 1,4-dioxenes, resulting from [4 + 2]-cycloaddition, oxetanes, arising by Paterno-Buchi processes, and beta-hydroxy-gamma-ketoesters, generated by SET-promoted Claisen-type condensation. These competitive pathways leading from the excited states of the 1,2-diketones to these products are influenced by solvent polarity and the nature of the silyl ketene acetal and 1,2-diketone. The Claisen-type condensation process, following an SET desilylation pathway and predominating when the photoreactions are carried out in the polar solvent acetonitrile, represents an efficient method to prepare a variety of diversely substituted beta-hydoxy-gamma-ketoesters.

A facile approach to the preparation of bis-crown ethers based on SET-promoted photomacrocyclization reactions.

A novel methodology for the synthesis of bis-crown ethers has been developed. The preparative route takes advantage of an efficient single electron transfer promoted photomacrocyclization reaction of polyether branched bisphthalimides which contain alpha-trimethylsilylmethyl groups at terminal positions. The generality of the methodology was demonstrated by its application to the synthesis of symmetric and unsymmetric bis-crown ethers of various ring sizes. Finally, the metal cation binding and fluorescence emission properties of the bis-crowns, prepared by using the developed procedure, were briefly explored.