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color="#000000"><b>Seminar on</b></font></div>
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color="#000000"><b>Modern Optics and Spectroscopy</b></font></div>
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<div align="center"><font face="Times New Roman"
color="#000000"><b>Fluorescence Spectra of Single-Walled Carbon
Nanotubes: From Discovery to Applications</b></font></div>
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<div align="center"><font face="Times New Roman"
color="#000000"><b>Bruce Weisman</b>, Rice
University<i>,</i></font></div>
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<div align="center"><font face="Times New Roman"
color="#000000">Tuesday , October 7, 2008</font></div>
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<div align="center"><font face="Times New Roman" color="#000000">12:00
- 1:00 p.m.</font></div>
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<div><font face="Times New Roman" color="#000000">Single-walled carbon
nanotubes (SWCNTs) are artificial nanostructures composed of carbon
atoms covalently bonded into cylindrical tubular frameworks with large
aspect ratios. They display a range of remarkable mechanical, thermal,
electronic, and optical properties that have attracted intense
interest among basic and applied researchers. SWCNTs exist in a
variety of well defined structures differing in diameter and chiral
angle. Most of these forms are semiconducting, with band gaps that
depend on nanotube physical structure. A seminal event in SWCNT
research was the discovery and structural assignment of near-infrared
photoluminescence (fluorescence) spectra of disaggregated
semiconducting nanotubes. This spectral assignment process and several
subsequent applications will be reviewed. In one application,
near-IR fluorescence microscopy is used to investigate the
photophysical properties of individual SWCNTs. Calibrated photometric
measurements on selected nanotubes provide absolute intrinsic values
of fluorescence action cross-sections as a function of
(<i>n</i>,<i>m</i>) structure. To quantify the extrinsic variations in
these values, fluorimetric brightness has been measured for more than
400 (10,2) nanotubes whose lengths were individually deduced from
translational diffusion constants determined by trajectory analysis.
Individual nanotubes were also observed in fluorescence microscopy
while they were exposed to chemical reactants that quench the
emission. Stepwise changes in emission intensity were clearly observed
and identified as single-molecule reaction events. Analysis of the
step heights reveals that each sidewall reactive event quenches
excitons in a ~100 nm region of the nanotube surrounding the reaction
site. Another application area involves the development of near-IR
fluorimetry into a rapid, sensitive, and automated method for
quantitative (<i>n</i>,<i>m</i>)-level analysis of bulk SWCNT samples.
Near-IR fluorescence is also proving useful in developing SWCNT
biomedical applications. In the first observation of nanotubes inside
a living organism, SWCNTs have been imaged inside fruit fly larvae
that had been fed nanotubes in their food. Individual nanotubes could
be imaged and structurally identified inside dissected tissue
specimens.</font></div>
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<div align="center"><font face="Times New Roman" color="#000000">Grier
Room, MIT Bldg 34-401</font></div>
<div align="center"><font face="Times New Roman"
color="#000000">Refreshments served after the lecture</font></div>
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