CHEM 548: Materials Chemistry

Lecture 21: Organic Conductors

Mon 11/16/2026 · Meeting 23

Reading: Woodward, Karen, Evans, and Vogt, Solid State Materials Chemistry
Ch. 10 §§10.5–10.6

Conductivity of Select Materials

Table of conductivities for selected materials in siemens per meter, from silver at 6.2 times ten to the seventh down to Teflon at ten to the minus twenty-second, with doped polyacetylene at 8 times ten to the fourth.

Organic Conductors: From Polymers to Nanotubes

Learning Objectives

Explain how π-conjugation leads to delocalized molecular orbitals that form bands
Relate Peierls distortion and redox doping to the band gap and carrier formation in polymers
Define nanotube (n,m) indices and compute diameter and chiral angle
Predict metallic vs semiconducting behavior from the (n−m)/3 rule and E_g ∝ 1/d
Compare transport limits in polymers vs nanotubes and link back to structure

Why Organic Conductors?

Breaking the Paradigm

Traditional view: organics = insulators
1970s revolution: conjugated systems conduct
Conductivity spans 15 orders of magnitude
2000 Nobel Prize in Chemistry

Key Advantages

Lightweight & flexible
Solution processable
Tunable properties
Applications: OLEDs, solar cells, sensors

Organic Electronics: Market Snapshot

Application Area	Estimated Market Size (USD)	Notes
OLED / Organic Electronics (displays, flexible devices)	~46B	By far the largest real-world use of organic conductors; includes OLED materials and organic layers in display stacks.
Conductive Polymers (coatings, EMI shielding, antistatic, electronics)	~5B	Pure organic conductor materials used in coatings, components, printed electronics interfaces.
Organic Photovoltaics / Polymer Solar Cells	~1.7B	Rapid growth; still small compared with displays but expanding quickly.
Sensors, Actuators, Printed Electronics	~0.8B	Includes wearables, IoT devices, smart materials using organic conductors.
Bioelectronics / Medical & Wearable Interfaces	0.1–1B (varies)	Highly specialized; smaller but high-value and growing.

OLED and organic electronics, meaning displays and flexible devices, are roughly a forty-six billion dollar market: by far the largest real-world use of organic conductors; it includes OLED materials and organic layers in display stacks.

Conductive polymers for coatings, EMI shielding, antistatic, and electronics: roughly five billion — pure organic conductor materials used in coatings, components, printed electronics interfaces
Organic photovoltaics and polymer solar cells: roughly 1.7 billion — rapid growth; still small compared with displays but expanding quickly
Sensors, actuators, and printed electronics: roughly 0.8 billion — wearables, IoT devices, smart materials using organic conductors
Bioelectronics, medical and wearable interfaces: 0.1 to 1 billion depending on how you count — highly specialized; smaller but high-value and growing

To understand how an organic material can conduct at all, start with the simplest comparison: Teflon next to polyacetylene.

Teflon vs. trans-Polyacetylene

The Teflon repeat unit, a saturated CF2 chain, beside trans-polyacetylene drawn both with explicit carbons and hydrogens and as the alternating single and double bond zigzag chain.

The $\pi$ and $\pi^*$ Bands of trans-Polyacetylene

The C2H2 repeat unit, an energy-level stack of filled sigma and pi bands and empty pi-star and sigma-star bands, the pi and pi-star crystal orbitals at k equals zero and k equals pi over a, and the resulting pi and pi-star band dispersion with the Fermi level in the gap.

The crystal orbitals corresponding to the π MOs are shown at k = 0 and π/a.

At k = 0 the band formed from the π MO is completely bonding and will have the lowest possible energy; the band formed from the π* MO is completely antibonding and will have the highest possible energy.

At k = π/a the interaction between carbon atoms in neighboring unit cells changes sign, so the band formed from the π MO runs uphill from k = 0 to π/a and the band formed from the π* MO runs downhill.

The individual widths of the π and π* bands are estimated to be 5-6 eV.

If all carbon-carbon distances were identical, the bands would touch at k = π/a and trans-polyacetylene would be a metal.

But the distances alternate between 1.44 Å (single bond) and 1.36 Å (double bond); this alternation lifts the degeneracy and is responsible for the presence of a band gap of 1.7-1.8 eV.

This is a classic case of a Peierls distortion.

A band gap near two electron volts is a semiconductor, not a metal, so we need doping.

Doping Polyacetylene: Polarons, Bipolarons, Solitons

Oxidative doping sequence for polyacetylene: pristine chain, polaron after one oxidation, bipolaron after a second oxidation, conversion to solitons, and finally two separated charged solitons.

PEDOT:PSS

PEDOT and PSS Structures

Chemical structures of the PEDOT chain, positively charged thiophene rings with ethylenedioxy bridges, above the PSS chain, a polystyrene backbone carrying sulfonate and sulfonic acid groups.

Key Advantage #1: Water Processable

The single biggest reason for commercial success

Processing Methods

Solution casting at room temperature
Spin coating
Screen printing
Roll-to-roll compatible
Standard coating tools

Competitive Advantage

Other conducting polymers require:

Harsh organic solvents
In-situ oxidative polymerization
Special handling conditions

Key Advantages #2 & #3: Stability & Film Quality

Advantage 2, air stable: unlike most conducting polymers that degrade in oxygen or moisture, storage without special precautions, standard shipping, long shelf life. Advantage 3, superior films: optically clear, uniform thickness, low surface roughness, no cracking or defects.

Key Advantages #4 & #5: Tunability & Industry Fit

Advantage 4, tunable conductivity: adjusting the PEDOT to PSS ratio or adding secondary dopants like DMSO, ethylene glycol, or sorbitol takes films from 1 to over 1000 siemens per centimeter, shown as a bar chart. Advantage 5, industry compatible: OLED displays, touch panels, photovoltaics, sensors, antistatic coatings.

Single-Walled and Multi-Walled Carbon Nanotubes

Four-panel diagram: graphene multi-layered gives graphite; graphene rolled up gives a single-walled carbon nanotube; multi-layering the tube gives multi-walled carbon nanotubes.

Defining the Chiral Vector

A graphene sheet with the origin O, the chiral vector C h drawn to the lattice point labeled 6 comma 3, the perpendicular translational vector T to 4 comma minus 5, and the Cartesian formulas for the lattice vectors a1 and a2.

The way you wrap up the shee of graphene determines the electronic properties.

Circumferential vector: can be expressed as a linear sum of the a and b lattice vectors of graphene, in the general form C = 6a + 3b, where 6 and 3 are integers
Translational vector T: perpendicular to C, links two equivalent sites
The rectangle formed by C and T defines the unit cell of the carbon nanotube
Imagine excising a strip from the graphene sheet — width defined by C, infinite length — and rolling it up into a tube by connecting opposite sides
The structure is completely defined by the integers 6 and c, expressed using the notation (n,m), where n is the a1 integer and m is the a2 integer

Let's wrap our first tube: a (10,0) zigzag.

Wrapping the (10,0) Zigzag Nanotube

A graphene sheet with a highlighted strip whose chiral vector C h equals 10 comma 0 runs along a1; a click plays the source's wrapping animation frame for the (10,0) zigzag single-walled nanotube.

Wrapping the (10,10) Armchair Nanotube

A graphene sheet with a diamond-shaped region whose chiral vector C h equals 10 comma 10 runs along a1 plus a2; a click plays the source's wrapping animation frame for the (10,10) armchair single-walled nanotube.

Wrapping the (10,5) Chiral Nanotube

A graphene sheet with the wrapping region for chiral vector C h equals 10 comma 5, between the zigzag and armchair directions; a click plays the source's wrapping animation frame for the (10,5) chiral single-walled nanotube.

The (n,m) Map: Metallic or Semiconducting

The graphene sheet labeled with every (n,m) lattice point from (0,0) to (11,0), the zigzag edge along (n,0) and the armchair line along (n,n); red dots mark the metallic tubes where n minus m equals 3q, open circles the semiconductors.

Graphene's Dirac Points

Three-dimensional plot of graphene's pi and pi-star bands over the Brillouin zone, touching at the K and K-prime Dirac points, with crystal-orbital insets at Gamma and a note that band energies change linearly with k away from the Dirac points.

Why Some Nanotubes Are Metallic

Metallic or Semiconducting?

Screenshot of the Wolfram demonstration Brillouin Zone of a Single-Walled Carbon Nanotube with sliders at n equals 3, m equals 3: the allowed k lines cut through the K points of the hexagonal zone; a click moves the sliders to n equals 4, m equals 2, where the lines miss the Dirac points.

Carbon Nanotube Synthesis

Diagram of the standard chemical vapor deposition method for synthesizing carbon nanotubes: hydrocarbon and inert gas flow through a furnace at 500 to 1000 degrees Celsius over catalyst particles on a substrate, with base-growth and tip-growth mechanisms shown below.

Separating Metallic from Semiconducting Tubes

$Ultracentrifuge separation, with a density-gradient centrifuge tube and absorbance spectra, beside chromatographic separation, with column fractions and bottles of sorted metallic and semiconducting nanotube suspensions.$

Carbon Nanotube Markets

Application Area	Estimated Market Size (USD)	Notes
CNT-enhanced composites (plastics, automotive, aerospace, sports equipment)	~1.2–1.5B	Largest current CNT use; small CNT loadings improve conductivity, strength, ESD resistance; used in automotive fuel systems, EV lightweighting, structural materials.
CNT conductive additives for Li-ion batteries	~0.9–1.1B	Fastest-growing segment; CNTs used as conductive networks in battery cathodes/anodes; driven by EV growth; increasingly replacing carbon black in high-performance cells.
Transparent / conductive films & coatings	~0.2–0.3B	Used in flexible displays, touch panels, heaters; CNT films compete with ITO in specialty applications where flexibility or durability is required.
Sensors and electronics (RF devices, nanosensors, interconnects)	~0.1–0.2B	Includes strain sensors, biosensors, gas sensors, and early nanoelectronic components; small market but high R&D intensity.
CNT powders, inks, dispersions	~0.1B	Base materials sold as powders, masterbatches, dispersions; sold to electronics, composites, and energy manufacturers.

CNT-enhanced composites, in plastics, automotive, aerospace, and sports equipment, are roughly a 1.2 to 1.5 billion dollar market: the largest current CNT use; small CNT loadings improve conductivity, strength, ESD resistance; used in automotive fuel systems, EV lightweighting, structural materials.

CNT conductive additives for lithium-ion batteries: roughly 0.9 to 1.1 billion — the fastest-growing segment; conductive networks in battery cathodes and anodes; driven by EV growth; increasingly replacing carbon black in high-performance cells
Transparent conductive films and coatings: roughly 0.2 to 0.3 billion — flexible displays, touch panels, heaters; CNT films compete with ITO in specialty applications where flexibility or durability is required
Sensors and electronics, meaning RF devices, nanosensors, and interconnects: roughly 0.1 to 0.2 billion — strain sensors, biosensors, gas sensors, and early nanoelectronic components; a small market but high R&D intensity
CNT powders, inks, and dispersions: roughly 0.1 billion — base materials sold as powders, masterbatches, dispersions to electronics, composites, and energy manufacturers

That brings us to your practice questions.

Practice questions

Work the Lecture 21 practice questions before the next class. They cover π-conjugation and band formation in trans-polyacetylene, the Peierls distortion and the band gap it opens, redox doping with polarons, bipolarons and solitons, PEDOT:PSS and why it is water processable, the nanotube chiral vector and (n,m) indices, and the rule that decides whether a tube is metallic or semiconducting.

Open the Lecture 21 practice questions

Every question carries a worked explanation, so you can check your reasoning as you go.