Web Release Date: February 28,
Single-Molecule Spectroscopy Reveals the Conformational Heterogeneity of Conducting Polymers Encapsulated within Hollow Silica Spheres
and
Instituto de Tecnología Química CSIC-UPV, Universidad Politécnica de Valencia, 46022 Valencia, Spain,
Departament de Química, Universitat Aut
noma de Barcelona, 08193 Cerdanyola del Vallès, Spain,
ICFO-Institut de Ciències Fotniques, Mediterranean Technology Park, 08860 Castelldefels, Spain, and
ICREA-Institució Catalana de Recerca i Estudis Avançats, 08015 Barcelona, Spain
Received: September 13, 2007
In Final Form: December 24, 2007
Abstract:
Poly-2,6-naphthylidenevinylene (PNV) has been synthesized inside microporous hollow silica spheres of a
uniform diameter of 600 nm. The spheres obtained by acid hydrolysis followed by basic condensation of
phenyltrimethoxysilane and final aerobic calcination at 550 
C have a specific surface area (SBET) of 482 m2
g-1, have an average pore size of 6.8 Å, and are nonfluorescent. Adsorption of 2,6-bis(bromomethyl)naphthalene
as PNV precursor and subsequent room-temperature treatment with potassium tert-butoxide renders PNV
inside the hollow spheres. Use of small monomer amounts allows preparation of silica spheres with only one
or very few encapsulated polymers, as revealed by single-molecule fluorescence spectroscopy. Fluorescence
intensity and polarization experiments on individual PNV molecules within the spheres uncover different
spectroscopic behaviors arising from the heterogeneous distribution of polymer chain conformations. Tight-coiled PNV molecules fluoresce from a small number of emitting sites due to efficient excited-state energy
funneling, whereas multiple emitter behavior is found for extended polymer chains. Coexistence of both
extended and coiled segments in individual polymers accounts for the intermediate fluorescing properties
encountered for a significant portion of PNV molecules within the particles.
Download the full text: PDF | HTML
