Controlling supramolecular structures in iron tetrasulfonated phthalocyanine films through pH variation: implications for thin-film device performance

Abstract

Improving the performance of thin film-based devices is a crucial factor for their successful application, mainly for organic electronic semiconductors. The adjustment of supramolecular structuring of thin films plays a role in the optical and electrical properties. In this sense, we investigated how various pH values, such as 2.5, 6.0, and 9.0, of the solutions influenced the growth of iron tetrasulfonated phthalocyanine (FeTsPc) Layer-by-Layer (LbL) films and their respective supramolecular structures as well as their electrochemical properties. The supramolecular structures were evaluated via UV-vis absorption spectroscopy, quartz crystal microbalance (QCM), micro-Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and cyclic voltammetry. The different pH values of the solution induce different degrees of molecular aggregation for FeTsPc (monomer, dimer, and aggregate formation). For instance, the higher the pH, the higher the aggregation. Films produced at pH 2.5 were organized preferentially with the molecules perpendicular to the substrate, while films at pH 6.0 and 9.0 were organized preferentially with the molecules parallel to the substrate. Besides, the film produced at pH 2.5 results in higher film thickness, higher stability, and better electrocatalytic behavior for the electrochemical detection of catechol. The results presented here enhance the understanding of nanostructured films, helping to harness supramolecular organization to improve the performance of thin-film devices.