Tuning hybrid porphyrin-melanin films <i>via</i> supramolecular approach

The search for novel self-assembled materials has brought particular attention towards functional melanin-like polymers able to form robust underwater adhesive coatings on various substrates. In this scenario, the realization of hybrid porphyrin-melanin like films can gather attention by the well-known photophysical and chemical properties of porphyrinoid systems. Thus, in this paper we aim to synthesize functionalized melanin-like films on glass substrates by using four different cationic porphyrins: H2T4, CuT4, ZnT4 and SnT4. Alongside the porphyrins, we also investigated the effects of adding amine-rich molecules such as spermine on the hierarchical self-assembly of the hybrid melanin-like@glass films. We have set up a simple and feasible synthetic method which consists of dipping the glass substrate in either a PBS buffer solution of porphyrin/L-DOPA or porphyrin/spermine/L-DOPA with an incubation time of 14 days. The obtained functionalized glass substrate was characterized by UV-vis spectroscopy to ensure the deposition of the hybrid porphyrin-melanin film and by AFM to study its surface morphological properties. Our analysis revealed no significant differences in the surface textures of the hybrid film obtained with H2T4 and CuT4, contrary to both the ZnT4 and SnT4 films, which exhibited an increase in all surface parameters on account of their different coordination number. On the other hand, the addition of spermine involved a general flattening of the analyzed surface area in all instances. Overall, our results can be exploited in the ever-growing materials science field to develop tailored and robust functionalized melanin-like films.