Formation of C H Ablation of Graphite, Coal or C Particles Suspended in Selected Solvents - Polyynes: Synthesis, Properties, and Applications - page 124

studied laser ablation of small graphite particles in solutions using a focused
694 nm ruby laser beam of 500 J/cm 2 with a long pulse period of about 1ms.
In the product analysis, using the high-performance liquid chromatography
(HPLC), they obtained three peaks of C 60 ,C 70 , and C 80 -C 90 fullerenes in
toluene solution. They found that the relative intensity of C 70 peak was
unusually stronger than that of more stable C 60 peak. Gaumet et al. [3]
studied laser ablation of a graphite cylinder in benzene using a focused 266,
532, and 1064 nm YAG laser (180mJ/pulse) with a short pulse period of
about 10 ns. On the basis of a product analysis using gas chromatography/

mass spectrometry (GC/MS), they obtained experimental evidence for the
formation of small C 1 ,C 2 ,C 3 , and C 4 carbon clusters by laser vaporization
of graphite in solution. Two types of laser reactions were observed: addition
of carbon clusters to a phenyl radical and aggregation of carbon clusters
resulting in hydrogen-capped C 2n H 2 (n 4 and 6) polyynes.

Due to its unique geometrical structure, polyynes are ranked on promis-
ing one-dimensional conducting materials, which can be used for ''mole-
cular wires'' [4]. Unlike fullerenes and carbon nanotubes, however, the
existence of polyynes is still disputed. Therefore, studies on polyynes are
rather rare compared with those on fullerenes and carbon nanotubes. The
synthesis of mixtures of polyynes up to 32 carbon atoms was reported by
Eastmond et al. in 1972 [5]. C 2n H 2 polyynes were prepared using copper
chloride (Hay coupling) and mixtures of acetylenic carbon compounds
that contained 2 to 16 acetylene units (Et) 3 Si-(C

¼

C) n -Si(Et) 3 : (Et, ethyl).
Synthesis of polyynes via Hay coupling must be carried out at low temper-
ature, because short-chain polyynes are only stable at low temperatures.
Since multisteps are required for the synthesis of long-chain polyynes via
Hay coupling, laser ablation in solutions at room temperature is a new
promising technique for the one-pot synthesis of polyynes.
We have recently studied laser ablation of graphite and C 60 particles
suspended in solutions [6,7]. It was found that hydrogen-capped polyynes
(C 2n H 2 : n

¼

4-8) were produced from graphite particles suspended in
benzene, toluene, or hexane solution [6], while C 2n H 2 (n

¼

4-6) polyynes
were formed from C 60 in hexane or methanol solution [7]. Cataldo [8,9] has
recently synthesized C 2n H 2 (n ¼ 2-9) polyynes by a submerged electric arc

discharge in organic solvents.
In this review, in addition to more detailed experimental data for the
synthesis of polyynes by laser ablation of graphite in solutions, new data
for Indonesian and Australian coals are reported. In the experiments for
graphite, besides benzene, toluene, and hexane used in our previous report
[6], cyclohexane and methanol are used as solvents. It is known that
long C 2n F 2 polyynes are generated by laser ablation of graphite in an
F-containing gas [10]. Therefore, such F-containing solvents as hexafluoro-
benzene, perfluorooctane, and perfluorodecaline are also used as new
solvents. The absorbances of polyynes in each solvent are measured not only
at 355 nm laser irradiation reported previously [6] but also at 266, 532, and