Amphiphilic porphyrin-cardanol derivatives in Langmuir and Langmuir–Blodgett films applied for sensing

This study presents the preparation of a nanostructured films with an amphiphilic meso-porphyrin whose side chains are derived from cardanol, a byproduct of the cashew industry. The Langmuir films were prepared on acidified water to reducing the self-aggregation of the complex and the mean molecular area for the meso-porphyrin measured by surface pressure isotherms was 177 Å2 and confirmed by compressibility modulus. The 700 nm band observed in the Langmuir films supports the coexistence of monomers and dimers similar to the spectra of the solution (CHCl3/CH3COOH). The formation of bright block domains with different sizes and shapes for the monolayer disappears after surface pressure starts to increase (π ≥ 2 mN m−1), as observed by Brewster angle microscopy measurements. Results of UV–vis spectra of the Langmuir films and FTIR reflection of the Langmuir–Blodgett (LB) films of meso-porphyrin indicated that the molecules exhibit preferential orientation with the planes perpendicular to the water (Langmuir) and parallel to the substrate (LB) surface. The LB films were tested as a promethazine sensor, which detected a concentration of 2 μM, a value greater than those obtained by other nanostructured systems.