  In recent years there has been a growing interest in sp-carbon chains as
possible novel nanostructures. An example of sp-carbon chains are the so-called
polyynes, characterized by the alternation of single and triple bonds that can
be synthesized by pulsed laser ablation in liquid (PLAL) of a graphite target.
In this work, by exploiting different solvents in the PLAL process, e.g. water,
acetonitrile, methanol, ethanol, and isopropanol, we systematically investigate
the solvent role in polyyne formation and stability. The presence of methyland
cyano-groups in the solutions influences the termination of polyynes, allowing
to detect, in addition to hydrogen-capped polyynes up to HC22H, methyl-capped
polyynes up to 18 carbon atoms (i.e. HCnCH3) and cyanopolyynes up to HC12CN.
The assignment of each species was done by UV-Vis spectroscopy and supported by
density functional theory simulations of vibronic spectra. In addition,
surface-enhanced Raman spectroscopy allowed to observe differences, due to
different terminations (hydrogen, methyl-and cyano group), in the shape and
positions of the characteristic Raman bands of the size-selected polyynes. The
evolution in time of each polyyne has been investigated evaluating the
chromatographic peak area, and the effect of size, terminations and solvents on
polyynes stability has been individuated.
