Effect of Acetylene Links on Electronic and Optical Properties of Semiconducting Graphynes

The family of graphynes, novel two-dimensional semiconductors with various and fascinating chemical and physical properties, has attracted great interest from both scientific and industrial communities. Currently, the focus is on graphdiyne or graphyne-2. In this work, we systematically study the effect of acetylene, i.e., carbon-carbon triple bond, links on the electronic and optical properties of a series of graphynes (graphyne-n, where n = 1-5, the number of acetylene bonds) using ab initio calculations. We find an even-odd pattern, i.e., n = 1, 3, 5 and n = 2, 4 having different features, which has not been discovered in studying graphyne or graphdiyne alone. It is found that as the number of acetylene bonds increases, the electron effective mass increases continuously in the low-energy range because of the flatter conduction band induced by the longer acetylene links. Meanwhile, longer acetylene links result in a larger red shift of the imaginary part of the dielectric function, loss function, and extinction coefficient. In this work, we propose an effective method to tune and manipulate both the electronic and optical properties of graphynes for the applications in optoelectronic devices and photochemical catalysis.