The electronic and geometrical structure of 1,4-bis(phenylethynyl)-2,5-bis(ethoxy)benzene (PEEB) molecules adsorbed on a Au(111) surface is investigated by low temperature scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) in conjunction with density-functional-based tight-binding (DFTB) simulations of the density of states and the interaction with the substrate. Our density functional theory calculations indicate that the PEEB molecule is physisorbed on the Au(111) substrate, with negligible distortion of the molecular geometry and charge transfer between molecule and substrate.