1 Introduction
Light-emitting polymers with a π-conjugated structure have attracted considerable
interest in the fields of both fundamental science and applied research owing to their
fascinating one-dimensional (1D) characteristics and potential optoelectronic
applications [1–6]. Figure 1 shows the chemical structures of a few examples of
π-conjugated light-emitting polymers: polythiophene (PTh), poly(3-alkylthiophene)
(P3AT), poly(3,4-ethylenedioxythiophene) (PEDOT), poly(p-phenylenevinylene)
(PPV), and poly[2-methoxy-5-(2
0 -ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV).
The π-conjugated structure of light-emitting polymers refers to the alternation of
single and double covalent bonds between adjacent carbon atoms [7]. This π-conjugation leads to delocalized π-electrons along the polymeric main chains, which play
an important role in the electronic and optical properties of light-emitting polymers
[8]. The electronic structures of π-conjugated polymers are successfully described by
the Su–Schrieffer–Heeger (SSH) Hamiltonian model [9–11]. As a consequence of the
π-conjugated structure, these light-emitting polymers have a semiconducting band
gap. Both theoretical and experimental studies have been conducted on chemical
processes for engineering the energy band structure of π-conjugated polymers
[10, 12–24]. Thus, the optical and electrical properties of π-conjugated polymers
can be varied by controlling the energy band structure and by chemical doping.
With rapid developments in nanoscience and nanotechnology, various
nanostructures, including nanotubes (NTs), nanowires (NWs), and nanoparticles
(NPs), have been fabricated using light-emitting polymers [4–6]. The intrinsic
characteristics of π-conjugated polymer nanostructures can be controlled through
the physical dimensions, chemical processes, and post-synthetic treatments.
This review article introduces and summarizes the fabrication, characterization,
and modification processes as well as optoelectronic applications of various lightemitting polymer nanostructures.
2 Synthetic Methods for Nanostructures
π-Conjugated light-emitting polymer nanostructures, including NTs, NWs, and NPs
have been synthesized using template and template-free methods [5, 6, 25–29].
Recently, Jenekhe et al. reviewed various synthetic methods for 1D nanostructures
of π-conjugated molecular systems [30]. Template-based methods are categorized
into two sub-categories depending on the type of template, i.e., soft templates and
hard templates. Anodic aluminum oxide (Al 2 O 3 ), particle track-etched membrane,
mesoporous silica, microchannel array, and zeolite are typically employed as hard
templates. The synthesis of π-conjugated polymer NTs or NWs with hard templates
involves a combination of electrochemical [25, 31–33], chemical [34–37], and
organic vapor deposition [38] techniques. The formation of NTs or NWs and
their physical dimensions, such as diameter and length, are determined by the
Synthesis, Characteristics, and Applications of Intrinsically Light-Emitting. . .
203
Light-emitting polymers with a π-conjugated structure have attracted considerable
interest in the fields of both fundamental science and applied research owing to their
fascinating one-dimensional (1D) characteristics and potential optoelectronic
applications [1–6]. Figure 1 shows the chemical structures of a few examples of
π-conjugated light-emitting polymers: polythiophene (PTh), poly(3-alkylthiophene)
(P3AT), poly(3,4-ethylenedioxythiophene) (PEDOT), poly(p-phenylenevinylene)
(PPV), and poly[2-methoxy-5-(2
0 -ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV).
The π-conjugated structure of light-emitting polymers refers to the alternation of
single and double covalent bonds between adjacent carbon atoms [7]. This π-conjugation leads to delocalized π-electrons along the polymeric main chains, which play
an important role in the electronic and optical properties of light-emitting polymers
[8]. The electronic structures of π-conjugated polymers are successfully described by
the Su–Schrieffer–Heeger (SSH) Hamiltonian model [9–11]. As a consequence of the
π-conjugated structure, these light-emitting polymers have a semiconducting band
gap. Both theoretical and experimental studies have been conducted on chemical
processes for engineering the energy band structure of π-conjugated polymers
[10, 12–24]. Thus, the optical and electrical properties of π-conjugated polymers
can be varied by controlling the energy band structure and by chemical doping.
With rapid developments in nanoscience and nanotechnology, various
nanostructures, including nanotubes (NTs), nanowires (NWs), and nanoparticles
(NPs), have been fabricated using light-emitting polymers [4–6]. The intrinsic
characteristics of π-conjugated polymer nanostructures can be controlled through
the physical dimensions, chemical processes, and post-synthetic treatments.
This review article introduces and summarizes the fabrication, characterization,
and modification processes as well as optoelectronic applications of various lightemitting polymer nanostructures.
2 Synthetic Methods for Nanostructures
π-Conjugated light-emitting polymer nanostructures, including NTs, NWs, and NPs
have been synthesized using template and template-free methods [5, 6, 25–29].
Recently, Jenekhe et al. reviewed various synthetic methods for 1D nanostructures
of π-conjugated molecular systems [30]. Template-based methods are categorized
into two sub-categories depending on the type of template, i.e., soft templates and
hard templates. Anodic aluminum oxide (Al 2 O 3 ), particle track-etched membrane,
mesoporous silica, microchannel array, and zeolite are typically employed as hard
templates. The synthesis of π-conjugated polymer NTs or NWs with hard templates
involves a combination of electrochemical [25, 31–33], chemical [34–37], and
organic vapor deposition [38] techniques. The formation of NTs or NWs and
their physical dimensions, such as diameter and length, are determined by the
Synthesis, Characteristics, and Applications of Intrinsically Light-Emitting. . .
203