Optical Studies of Semi-conducting Polymers

Background

Time resolved photoluminescence and photoinduced absorption studies of light emitting polymers provide insight into fundamental processes of charge recombination and light emission.

Recent Advances

Exciton dynamics in poly(p-pyridyl vinylene)

J. W. Blatchford, S. W. Jessen, L. B. Lin, J. J. Lih, T. L. Gustafson
    Department of Physics, The Ohio State University, Columbus, Ohio 43210-1106
A. J. Epstein
    Department of Physics, The Ohio State University, Columbus, Ohio 43210-1106
    Department of Chemistry, The Ohio State University, Columbus, Ohio 43210-1106
D. K. Fu, M. J. Marsella, T. M. Swager, A. G. MacDiarmid
    Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104–6323
S. Yamaguchi, and H. Hamaguchi
    Kanagawa Academy of Science and Technology, KSP East 301, 3-2-1 Sakato, Kawasaki 213, Japan

(Received 30 June 1995)

We present results of picosecond photoinduced absorption (PA) and time-resolved photoluminescence studies on solid and solution forms of poly(p-pyridyl vinylene). The nearly identical PA response of all forms of the polymer reflects the generation of the same primary
photoexcitation, a Couloumbically bound intrachain singlet exciton, and the absence of exotic species such as interchain excimers. The time
dependence of the PA points to direct intersystem crossing as the origin of triplet excitons, ruling out generation of free carriers as a
precursor to exciton formation. ©1996 The American Physical Society.

Photoluminescence in pyridine-based polymers: Role of aggregates

J. W. Blatchford and S. W. Jessen
    Department of Physics, The Ohio State University, Columbus, Ohio 43210
L.-B. Lin and T. L. Gustafson
    Department of Chemistry, The Ohio State University, Columbus, Ohio 43210
D.-K. Fu, H.-L. Wang, T. M. Swager, and A. G. MacDiarmid
    Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104
A. J. Epstein
    Department of Physics
    Department of Chemistry, The Ohio State University, Columbus, Ohio 43210

(Received 31 May 1996)

We present a study of the morphology dependence of the photoluminescence (PL) properties of the pyridine-based polymers poly(p-pyridyl
vinylene), poly(p-pyridine), and poly(p-pyridyl vinylene p-phenylene vinylene) (PPyVPV). The photoluminescence of solution samples is
characterized by high quantum efficiency (>70% in PPyVPV), weak coupling to vibrational modes (Huang-Rhys parameter ~0.5) and a
single-exponential decay (radiative lifetime ~1 ns). On the other hand, film samples display strongly redshifted, featureless emission with low
quantum yield (<20%) and highly nonexponential decay dynamics. Through consideration of absorption and excitation spectra, the
``site-selectivity'' of the PL, and the concentration dependence of the PL spectrum, we demonstrate that the redshifted film spectra are a
result of the formation of low-energy aggregate sites due to strong interchain interactions. Time-resolved measurements suggest a longer
radiative lifetime for the aggregate vs solution, leading to the lower efficiency. Aggregate formation is found to be morphology dependent,
and is minimal in ``powder'' samples which are precipitated after polymerization. ©1996 The American Physical Society.

Spatially and temporally resolved emission from aggregates in conjugated polymers

J. W. Blatchford
    Department of Physics, The Ohio State University, Columbus, Ohio 43210-1106
T. L. Gustafson
    Department of Chemistry, The Ohio State University, Columbus, Ohio 43210-1173
A. J. Epstein
    Department of Physics and Department of Chemistry, The Ohio State University, Columbus, Ohio 43210-1106
D. A. Vanden Bout, J. Kerimo, D. A. Higgins, and P. F. Barbara
    Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455-0431
D.-K. Fu, T. M. Swager, and A. G. MacDiarmid
    Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323

(Received 13 May 1996)

We present results of cw, time-resolved, and spatially resolved spectroscopic studies of emission and absorption in a model conjugated
polymer, poly(p-pyridyl vinylene) (PPyV). The redshifted film spectra suggest the formation of aggregated regions. The ~4 x reduction in
emission efficiency in films vs solution is attributed to a longer radiative lifetime for aggregate excitons, as is evidenced by time-resolved
fluorescence measurements. We present direct optical imaging of aggregates in a conjugated polymer via near-field scanning optical
microscopy. The aggregate emission and absorption are found to be localized to partially aligned regions of the film ~200 nm in size.
©1996 The American Physical Society.

Publications

J.W. Blatchford, T.L. Gustafson, and A.J. Epstein, Electronic Structure of Pyridine-Based Polymers, Journal of Chemical Physics 105, 9214-9226 (1996).

J.W. Blatchford, S.W. Jessen, L.B. Lin, T.L. Gustafson, A.J. Epstein, D.K. Fu, H.L. Wang, T.M. Swager, and A.G. MacDiarmid, Aggregate Formation in Pyridine Based Polymers, Materials Research Society Symposium Proceedings 413, 671-676 (1996).

J.W. Blatchford, S.W. Jessen, L.B. Lin, J.J. Lih, T.L. Gustafson, A.J. Epstein, D.-K. Fu, M.J. Marsella, T.M. Swager, A.G. MacDiarmid, S. Yamaguchi, and H. Hamaguchi, Exciton Dynamics in Poly(p-pyridyl vinylene), Physical Review Letters 76, 1513-1516 (1996).

K. Kim, J.W. Blatchford, T.L. Gustafson, A.G. MacDiarmid and A.J. Epstein, Picosecond Photoinduced Absorption and Long-lived Effects in Polyaniline, Synthetic Metals 69, 247-250 (1995).

Created by Darren Gebler. Maintained by John Rohrbacher. Last updated 5/30/00.