1 3
Theor Chem Acc (2015) 134:109
DOI 10.1007/s00214-015-1704-9
REGULAR ARTICLE
Metallic and semiconducting 1D conjugated polymers based
on –S–C ≡ C– repeating units in poly(sulfur acetylide)
Károly Németh
1
Received: 20 May 2015 / Accepted: 17 July 2015 / Published online: 22 August 2015
© Springer-Verlag Berlin Heidelberg 2015
1 Introduction
Synthetic metals and semiconductors are an important fi eld
of materials chemistry and physics. These materials are
based on conjugated π -electron systems. On the one hand,
the various options of synthetic chemistry to link numerous
possible pieces of conjugated π -electron systems together
allow for tuning the properties of these materials. On the
other hand, band structure calculations allow for the theoretical design of conjugated π -electron systems with specifi c predefi ned properties [ 1 – 8 ]. Poly(sulfur nitride),
(SN) x , has been the earliest example of a synthetic metal
based on a 1D conjugated π -electron system [ 9 ]. It has fi rst
been synthesized [ 10 ] in 1910, but its conductivity has been
measured only in 1973 [ 11 ], and its superconductivity at
0.26 K has been discovered in 1975 [ 12 ]. Another signifi -
cant advance in the fi eld of quasi 1D (semi)conductors was
the synthesis and characterization of polyacetylene (CH) x
by Heeger, MacDiarmid, Shirakawa and coworkers [ 13 – 15 ]
in 1977. While (SN) x is a metal without doping, (CH) x is a
semiconductor with a 1.4 eV band gap [ 16 ]. Despite decades of work on conjugated polymers, (SN) x remains the
sole polymer that is metallic without doping. (CH) x and
other known conjugated polymers become metallic only
when doped, e.g., by iodine [ 16 ].
Peierls’ instability theorem from 1955 predicts [ 17 ] that
an equidistantly placed (quasi) 1D chain of identical atoms
with a single electron per atomic site is unstable and undergoes geometric rearrangements, such as bond-length alternation in a unit cell containing two atoms instead of one,
to stabilize itself. In fact, Peierls’ instability theorem is a
special case of the well-known Jahn–Teller distortion [ 18 ]
which states that a molecule with a degenerate ground state
is unstable and undergoes a geometric distortion until its
ground state becomes non-degenerate. Peierls’ instability
Abstract The existence and the properties of a new 1D
conjugated polymer, poly(sulfur acetylide), with –S–C ≡ C–
repeating unit are predicted on the basis of density functional theory calculations. Depending on the conformation
of the polymer, specifi cally on the C–S–C angles, the corresponding material is either a metallic conductor (C–S–C
near linear) or a semiconductor (C–S–C not linear). It is
a semiconductor with 1.6 eV band gap in the minimum
energy conformation bent geometry. The polymer can be
stretched out at a relatively large and impractical energy
cost of 2.6 eV per –S–C ≡ C– unit upon which it becomes
a metallic conductor. However, this semiconductor–metal
transition appears to be unique in as much as it happens
along a bending mode of the polymeric backbone. This new
material appears to be easy to synthesize and is expected
to be stable under normal conditions. Despite its simplicity and close relation to other well-known 1D conjugated
polymers, such as poly(sulfur nitride) (SN) x , polyacetylene
(CH) x or polyyne (–C ≡ C–) x , poly(sulfur acetylide) still
remains to be explored.
Keywords Poly(sulfur acetylide) · Conjugated polymer ·
Organic semiconductor · Band structure design
Electronic supplementary material The online version of this
article (doi: 10.1007/s00214-015-1704-9 ) contains supplementary
material, which is available to authorized users.
Published as part of the special collection of articles “Festschrift
in honour of P. R. Surjan”.
* Károly Németh
nemeth@agni.phys.iit.edu
1
Physics Department , Illinois Institute of Technology ,
Chicago , IL 60616 , USA
199
Reprinted from the journal
Theor Chem Acc (2015) 134:109
DOI 10.1007/s00214-015-1704-9
REGULAR ARTICLE
Metallic and semiconducting 1D conjugated polymers based
on –S–C ≡ C– repeating units in poly(sulfur acetylide)
Károly Németh
1
Received: 20 May 2015 / Accepted: 17 July 2015 / Published online: 22 August 2015
© Springer-Verlag Berlin Heidelberg 2015
1 Introduction
Synthetic metals and semiconductors are an important fi eld
of materials chemistry and physics. These materials are
based on conjugated π -electron systems. On the one hand,
the various options of synthetic chemistry to link numerous
possible pieces of conjugated π -electron systems together
allow for tuning the properties of these materials. On the
other hand, band structure calculations allow for the theoretical design of conjugated π -electron systems with specifi c predefi ned properties [ 1 – 8 ]. Poly(sulfur nitride),
(SN) x , has been the earliest example of a synthetic metal
based on a 1D conjugated π -electron system [ 9 ]. It has fi rst
been synthesized [ 10 ] in 1910, but its conductivity has been
measured only in 1973 [ 11 ], and its superconductivity at
0.26 K has been discovered in 1975 [ 12 ]. Another signifi -
cant advance in the fi eld of quasi 1D (semi)conductors was
the synthesis and characterization of polyacetylene (CH) x
by Heeger, MacDiarmid, Shirakawa and coworkers [ 13 – 15 ]
in 1977. While (SN) x is a metal without doping, (CH) x is a
semiconductor with a 1.4 eV band gap [ 16 ]. Despite decades of work on conjugated polymers, (SN) x remains the
sole polymer that is metallic without doping. (CH) x and
other known conjugated polymers become metallic only
when doped, e.g., by iodine [ 16 ].
Peierls’ instability theorem from 1955 predicts [ 17 ] that
an equidistantly placed (quasi) 1D chain of identical atoms
with a single electron per atomic site is unstable and undergoes geometric rearrangements, such as bond-length alternation in a unit cell containing two atoms instead of one,
to stabilize itself. In fact, Peierls’ instability theorem is a
special case of the well-known Jahn–Teller distortion [ 18 ]
which states that a molecule with a degenerate ground state
is unstable and undergoes a geometric distortion until its
ground state becomes non-degenerate. Peierls’ instability
Abstract The existence and the properties of a new 1D
conjugated polymer, poly(sulfur acetylide), with –S–C ≡ C–
repeating unit are predicted on the basis of density functional theory calculations. Depending on the conformation
of the polymer, specifi cally on the C–S–C angles, the corresponding material is either a metallic conductor (C–S–C
near linear) or a semiconductor (C–S–C not linear). It is
a semiconductor with 1.6 eV band gap in the minimum
energy conformation bent geometry. The polymer can be
stretched out at a relatively large and impractical energy
cost of 2.6 eV per –S–C ≡ C– unit upon which it becomes
a metallic conductor. However, this semiconductor–metal
transition appears to be unique in as much as it happens
along a bending mode of the polymeric backbone. This new
material appears to be easy to synthesize and is expected
to be stable under normal conditions. Despite its simplicity and close relation to other well-known 1D conjugated
polymers, such as poly(sulfur nitride) (SN) x , polyacetylene
(CH) x or polyyne (–C ≡ C–) x , poly(sulfur acetylide) still
remains to be explored.
Keywords Poly(sulfur acetylide) · Conjugated polymer ·
Organic semiconductor · Band structure design
Electronic supplementary material The online version of this
article (doi: 10.1007/s00214-015-1704-9 ) contains supplementary
material, which is available to authorized users.
Published as part of the special collection of articles “Festschrift
in honour of P. R. Surjan”.
* Károly Németh
nemeth@agni.phys.iit.edu
1
Physics Department , Illinois Institute of Technology ,
Chicago , IL 60616 , USA
199
Reprinted from the journal