Effects of Metal−Ion Complexation for the Self-Assembled Nanocomposite Films Composed of Gold Nanoparticles and 3,8-Bis(terthiophenyl)phenanthroline-Based Dithiols Bridging 1 μm Gap Gold Electrodes: Morphology, Temperature Dependent Electronic Conduction, and Photoresponse

3,8-Bis(3′,4′-dibutyl-5′′-mercapto-2,2′:5′,2′′-terthiophen-5-yl)-1,10-phenanthroline (2) with a molecular length of 3.36 nm and its Ru(II), Fe(II), and Cu(II) complexes were treated with tert-dodecanethiol-protected active gold nanoparticles (Au-NPs) in an average size of 3.3 nm in the presence of two facing Au electrodes with a 1 × 1 μm2 gap. Stable self-assembled molecular junctions were produced, wherein dithiols-bridged Au-NPs were chemisorbed to the electrodes by means of Au−S-bonded contacts. SEM and AFM micrographs showed that different morphologies of the films were formed depending on the number of ligand 2 in the molecules and the coordination configurations of transition metal ions. Among them a relatively homogeneous granular thin film was obtained successfully in the case of the [Ru(bpy)2]2+ complex. Temperature-dependent current−voltage measurements for these junctions were performed in the temperature range of 8−300 K. The electronic conduction is dominated by the sum of tunneling and thermal excitation. Classical Arrhenius plots and their linear fits, wherein the temperature-independent tunneling current was deducted, were obtained to determine the average activation energies of these nanodevices. Photoresponsive properties of these self-assembled films were studied at different temperature (80, 160, and 300 K, respectively), where reversible and reproducible photoresponse can be recorded at room temperature in the presence of [Ru(bpy)2]2+ species. The comparison of results before and after metal−ion complexation reveals that the introduction of Ru(II) ion into the metal−molecule system can improve effectively the morphology of the self-assembled films and the overall conductivity, decrease the barrier for activation energy, and enhance the photoresponse of these nanodevices.