The spectral behavior of single terrylene molecules at a hexadecane-silica interface structure is studied. Different sample preparation techniques indicate that molecules close to a silica substrate in a hexadecane matrix are subject to additional dephasing or spectral diffusion. The temperature activation of the homogeneous line width of these molecules shows much reduced activation energies as compared to those of molecules in bulk hexadecane. These low-lying activation energies may be attributed to surface phonon states or local phonon modes particular to the interface structure. With the aid of a low-temperature scanning confocal microscope, the distance of single terrylene molecules to the silica surface can be measured with a precision of 60 nm. A drastic increase of the homogeneous line width for molecules with distances less than 150 nm to the silica surface is found.