Diacetylene
Diacetylene, also known as butadiyne, is the organic compound with the formula C4H2. It is the simplest compound containing two triple bonds and is the first in the series of polyynes, which are of theoretical but not of practical interest[1].
Occurrence
Diacetylene has been identified in the atmosphere of Titan and in the protoplanetary nebula CRL 618 by its characteristic vibrational spectrum. It is proposed to arise by a reaction between acetylene and the ethynyl radical (C2H), which is produced when acetylene undergoes photolysis. This radical can in turn attack the triple bond in acetylene and react efficiently even at low temperatures. Diacetylene has also been detected on the Moon[1].
Preparation
This compound may be made by the dehydrohalogenation of 1,4-dichloro-2-butyne by potassium hydroxide (in alcoholic medium) at ~70°C[1].
Polydiacetylenes
Polydiacetylenes (PDAs) are a family of conducting polymers closely related to polyacetylene. They are created by the 1,4 topochemical polymerization of diacetylenes. They have multiple applications from the development of organic films to immobilization of other molecules[2].
History
The first polydiacetylene to be discovered was Poly(1,6-bishydroxy hexa-2,4-diacetylene) by Gerhard Wegner in 1969. This was achieved by exposing crystals of 1,6-bishydroxy hexa-2,4-diyne to UV light. Polymerization was assumed to occur because of the spatial arrangement of diynes in the crystal, but this was not confirmed until 1972 when Raymond H. Baughman coined the term "topochemical polymerization" to describe polymerization due to spatial arrangement and put forth the spatial requirements needed for a polymerization of this sort[2].
Synthesis
Synthesis of polydiacetylenes occurs through topochemical polymerization of 1,3-diynes. Typically, this must occur in the solid state, because many diynes undergo both 1,2 and 1,4 polymerization in solution – such is the case with diiodobutadiyne, and other diynes with electron withdrawing substituents. The ideal arrangement of diynes in the solid state is a repeat distance of 5Å, a 45° tilt angle, and a 3.5Å distance between C1 of one monomer and C4 of the adjacent diyne monomer[2].
Properties and Applications
Polydiacetylenes exhibit thermochromism caused by twisting of the polymer backbone, changing the amount of conjugation in the system. Depending upon the structure of the monomer, the resulting PDA can have interesting properties such as formation of a vesicle or tube structure. The chromatic transition from blue to red phase of PDA is caused by the electronic structure of PDAs' backbone which is featured by the alternative carbon double bond and carbon triple bond. Upon exposure to the external stimuli such as thermal, chemical and mechanical stimulus, the conjugation effect will endow the chromatic properties to this type material[2].
Recent Research
Zhu et al. have recently published an article about the synthesis of polydiacetylene using copper catalyst. This is the first report on synthesis of polydiacetylenes in the solution phase[2]. Additionally, research has been conducted on the synthesis and solid-state polymerization of diacetylene derivatives, which are well known to polymerize topochemically in the solid state via ultraviolet (UV) irradiation or thermal annealing to afford polydiacetylenes (PDAs)[3].
Citations:
[1] https://en.wikipedia.org/wiki/Diacetylene
[2] https://en.wikipedia.org/wiki/Polydiacetylenes
[3] https://www.nature.com/articles/pj201667
[4] https://pubchem.ncbi.nlm.nih.gov/compound/1_3-Butadiyne
[5] https://pubs.acs.org/doi/10.1021/jacs.7b11255