Sean A. Vail

Synthesis, photochemistry and photophysics of stilbene-derivatized fullerenes

The photochemistry and photophysics of two sets of stilbene-derivatized fullerene isomers, in which stilbene is covalently linked to C60, are described. Synthesis and characterization of cis- and trans-stilbene substituted methanofullerenes 1 and 2, and cis- and trans-stilbene substituted fulleropyrrolidines 7 and 8 are described. While UV irradiation of the stilbene-substituted ketal precursors to 1 and 2 lacking the fullerene moiety afforded a photostationary state with 90:10 cis:trans ratio, similar to that of other model stilbene systems, direct and fluorenone-sensitized irradiation of 1 and 2 led to complete conversion to the trans isomer 2, as determined by HPLC analysis. The same results were obtained using cis-trans isomers 7 and 8, namely, the photostationary state on excitation below 350 nm is essentially 100% trans. No isomerisation in either system was obtained on excitation above 400 nm, where all the light is absorbed by the fullerene moiety. By analogy to previous studies of quenching of stilbene excited states, these results suggest that both singlet and triplet excited states of the trans-stilbene moiety in 2 and 8 are being quenched by intramolecular energy transfer to the attached C60, while the much shorter lived cis-stilbene excited states are not similarly quenched. Fluorescence studies on compound 8 support this hypothesis, since the characteristic fluorescence emission of trans-stilbene and trans-stilbene derivatives is not observed in the case of adduct 8. Because of the well established fact that trans-stilbene S1 states are longer lived than the S1 states of the corresponding cis isomers, rapid intramolecular singlet-singlet energy transfer to the appended C60 moiety, ket approximately 10(12) s(-1), is able to compete effectively with radiative and radiationless deactivation of the trans-stilbene S1 states in 2 and 8, but not in the corresponding cis isomers 1 and 7.

Nanostructured Surfaces for Microfluidics and Sensing Applications

The present work demonstrates the use of light to move liquids on a photoresponsive monolayer, providing a new method for delivering analyses in lab-on-chip environments for microfluidic systems. The light-driven motion of liquids was achieved on photoresponsive azobenzene modified surfaces. The surface energy components of azobenzene modified surfaces were calculated by Van Oss theory. The motion of the liquid was achieved by generation of a surface tension gradient by isomerization of azobenzene monolayers using UV and Visible light, thereby establishing a surface energy heterogeneity on the edge of the droplet. Contact angle measurements of various solvents were used to demonstrate the requirement for fluid motion.