Experimental
Measurement of the Binding Configuration
and Coverage of Chirality-Sorting Polyfluorenes on Carbon Nanotubes
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Abstract
Poly(9,9-dioctylfluorene-2,7-diyl)
(PFO) exhibits exceptional (<i>n</i>,<i>m</i>)
chirality and electronic-type selectivity
for near-armchair semiconducting carbon nanotubes. To better understand
and control the factors governing this behavior, we experimentally
determine the surface coverage and binding configuration of PFO on
nanotubes in solution using photoluminescence energy transfer and
anisotropy measurements. The coverage increases with PFO concentration
in solution, following Langmuir-isotherm adsorption behavior with
cooperativity. The equilibrium binding constant (PFO concentration
in solution at half coverage), <i>K</i><sub>A</sub>, depends
on (<i>n</i>,<i>m</i>) and is 1.16 ± 0.30,
0.93 ± 0.12, and 1.13 ± 0.26 mg mL<sup>–1</sup> for
the highly selected (7,5), (8,6), and (8,7) species, respectively,
and the corresponding PFO wrapping angle at low coverage is 12, 17,
and 14 ± 2°, respectively. In contrast, the inferred <i>K</i><sub>A</sub> for metallic nanotubes is nearly an order
of magnitude greater, indicating that the semiconducting selectivity
increases with decreasing PFO concentration. This understanding will
quantitatively guide future experimental and computational efforts
on electronic type-sorting carbon nanotubes
