2005 APS March Meeting
Monday–Friday, March 21–25, 2005;
Los Angeles, CA
Session J4: Conducting Polymers
11:15 AM–2:15 PM,
Tuesday, March 22, 2005
LACC
Room: 515A
Sponsoring
Unit:
DPOLY
Chair: Rachel Segalman, UC-Berkeley
Abstract ID: BAPS.2005.MAR.J4.5
Abstract: J4.00005 : Understanding the Intra- and Interchain Electronic Structure of Conjugated Polymers by Encapsulation in Mesoporous Silica
1:39 PM–2:15 PM
Preview Abstract
Abstract
Author:
Benjamin Schwartz
(Dept. Chem. \& Biochem., UCLA)
It is becoming increasingly clear that the morphology of a conjugated
polymer sample -- that is, the conformation of the individual polymer chains
and the way they pack together -- plays a direct role in the electronic
properties conjugated polymer films. In this talk, we describe the results
of work that provides a new method for controlling conjugated polymer
morphology and hence electronic properties: encapsulation of the polymer
chains into the channels of aligned mesoporous silicas. We find, for
example, that in small-pore silica samples where only a single polymer chain
can fit into each pore, essentially no polarons are formed upon excitation
and phenomena such as exciton-exciton annihilation that are prevalent in
bulk films do not occur. We also find that energy transfer (exciton
migration) occurs much more slowly along the polymer backbone than between
polymer chains, suggesting that the predominant mechanism for exciton
diffusion in bulk films is interchain Forster energy transfer. In
medium-sized pores that contain just a few polymer chains, we find that the
chains are still aligned by the encapsulation, and that polarons can be
formed upon directly upon excitation. We also see that exciton-exciton
annihilation is now possible, but that it occurs predominantly at kinks or
defect sites. In still larger pores, the polymer chains exhibit more bulk
film-like properties, including a high degree of photogeneration of polarons
and exciton-exciton annihilation. We also show that in the intermediate pore
size regime, the alignment of the polymer chromophores leads to
significantly lower lasing thresholds than bulk films of comparable optical
density, even though the physical density of the chromophores encapsulated
into the porous silica is much lower than that in bulk films. Taken
together, the results allow a new picture of how interactions between
polymer chains control the electronic properties of conjugated polymer
films.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2005.MAR.J4.5