Polyynes are 1D systems consisting of linear chains made of sp-hybridized carbon atoms. Their outstanding predicted properties attracted the interest of chemists and material scientists during the last decades. Vibrational spectroscopy emerged as the major way to investigate these properties. Indeed, polyynes are characterized by a Raman-active collective vibration (the ECC mode) whose position and shape are strongly influenced by chain structural and electronic properties.<br/>Pulsed laser ablation in liquid (PLAL) emerged as the most efficient and versatile physical synthesis technique of polyynes. The ablation process occurs by shining a high-intensity pulsed laser onto a graphite target immersed in a liquid that generates a plasma plume in which polyynes grow. However, the dynamics of the formation of polyynes during PLAL are still unclear. For this reason, we investigated the synthesis of polyyne by PLAL through synchrotron-based in situ UV resonance Raman (UVRR) spectroscopy. Thanks to the resonance condition and the tunability of the synchrotron radiation, we could detect and track the formation of size- and termination-selected polyynes with an improved time resolution (see Fig. 1a). The resonance enhancement allowed us to follow the first stages of the ablation when the concentration is too low for conventional Raman and without perturbing the ablation environment. We found that the production rate is higher in solvents with a high C/H ratio and low oxygen solubility (see Fig. 1b). We detected that polyynes production increases with the laser fluence and we discovered a threshold fluence when ablating at 1064 nm at which polyyne production is almost negligible. We also evaluate the production of single shots and the effect of diffusion mechanisms in PLAL.<br/>Our results shed light on the dynamics of the formation of polyyne by PLAL, improving the knowledge of this technique. Better control of the synthesis will simplify the scalability to an industrial level and a precise functionalization of polyynes.

In situ UV resonance raman spectroscopy to explore the formation mechanism of linear sp-carbon chains by pulsed laser ablation in liquid

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