Using ultrahigh vacuum (UHV) scanning tunneling microscopy (STM), many olefins have been shown to self-assemble on the hydrogen-passivated Si(100)-2 x 1 surface into one-dimensional nanostructures. This paper demonstrates that similar one-dimensional nanostructures can also be realized using alkynes. In particular, UHV STM, sum frequency generation (SFG), and density functional theory (DFT) are employed to study the growth mechanism and binding configuration of phenylacetylene (PA) one-dimensional nanostructures on the Si(100)-2 x 1:H surface. Molecular-resolution UHV STM images reveal the binding position and spacing of PA with respect to the underlying silicon dimer rows. Furthermore, UHV STM characterization of heteromolecular one-dimensional nanostructures of styrene and PA shows distinct electronic contrast between the two molecules, which is confirmed using simulated STM images derived from DFT and provides insight into the nature of PA binding to silicon. Additional evidence from SFG measurements corroborates the conclusion that the terminal carbon atoms of PA retain pi-conjugation following reaction to the Si(100)-2 x 1:H surface.