Identifying sp-sp2 carbon materials by Raman and infrared spectroscopies.

Two-dimensional (2D) materials composed of sp and sp(2) carbon atoms (e.g., graphyne and graphdiyne) show many interesting properties. These materials can be constructed through alkyne homocoupling; however, the occurrence of various side reactions increases the difficulty of their synthesis and structural characterization. Here, we investigate the thermodynamic properties and vibrational spectra of several aryl-alkynes. Both homocoupling and side reactions are found to occur spontaneously at room temperature in terms of thermodynamics. The calculated Raman spectra of the homocoupling products show regular changes with increasing polymerization degree. By rationalizing the vibrational modes of various oligomers, the Raman spectrum of a 2D sp-sp(2) carbon sheet is predicted; it exhibits three sharp peaks at 2241, 1560, and 1444 cm(-1). Although the target and byproducts display similar vibrational modes, a combination of Raman and infrared spectroscopies can be used to differentiate them. The theoretical results are then used to analyze the structure of a synthesized sample and provide useful information.