Substrate/solvent dependent THPP non-covalent functionalization of polyester support: A comparative physicochemical study with mercury readout

The non-covalent immobilization of porphyrins onto polymeric substrates introduces complex solvent-substrate interplay governing supramolecular organization. In this comparative physicochemical investigation, synergistic effects between these factors were screened by depositing tetrakis(4-hydroxyphenyl) porphyrin (THPP) onto commercially available polyester sheets. Polyethylene terephthalate (PET), polylactic acid (PLA), and PLA/PET multilayer were employed as solid supports, while ethyl acetate (AcOEt) or a binary ethanol/diethyl ether (EtOH/Et2O) mixture were selected as solvent system for porphyrin dispersion prior to deposition. The first is chosen as good solvent favouring the optimal solubilization of THPP, while the second one leverages the “good-bad” solvent effect, promoting controlled aggregation. A combination of analytical techniques, including attenuated total reflectance infrared (ATR-IR) and UV-vis spectroscopy, confocal dark-field microscopy, atomic force microscopy (AFM), wettability investigation, surface free energy (SFE) measurements, and Variable Angle Spectroscopic Ellipsometry (VASE), was employed to elucidate both morphological and chemical characteristics at the interface. These structural and interfacial parameters critically dictate porphyrin aggregation mode and binding site accessibility. The well-known selectivity of THPP for mercury ions was assessed as functional readout to compare the porphyrin response in the investigated substrate-solvent combinations. The homogeneous aggregate's distribution and smaller size found for THPP from EtOH/Et2O on PET made this system the most responsive, allowing also to evaluate its qualitative response toward other dications. The structure-property correlations presented in this study offer valuable design insights to guide the scalable non-covalent functionalization of porphyrin-polymer platform for a wide range of potential applications.