In situ synthesis of polyynes in a polymer matrix by pulsed laser ablation in liquid

Polyynes are finite chains formed by sp-hybridized carbon atoms with alternating single and triple bonds and displaying intriguing electronic and optical properties. Pulsed laser ablation in liquid (PLAL) is a well assessed technique for the physical synthesis of hydrogen-capped polyynes in solution, however, their limited stability prevents further exploitation in materials for different applications. In this work, polyynes in poly(vinyl alcohol) (PVA) were produced in a single-step PLAL process by ablating graphite directly in aqueous solution of PVA, investigating the role of polymer concentration. The presence of PVA solution, as a participating medium for PLAL, is shown to favour the formation of polyynes. The addition of Ag colloids to the aqueous PVA/polyynes solution allowed surface-enhanced Raman spectroscopy (SERS) measurements, carried out both on liquid samples and on free-standing nanocomposites, obtained after solvent evaporation. We show that polyynes in the nanocomposite remain stable at least for 11 months, whereas the corresponding PVA/Ag/polyynes solution displayed a strong polyyne reduction already after 3 weeks. These results open the view to further characterizations of the properties of polyyne-based films and materials.