Pyrene-naphthalene based Schiff Base: Smartphone integrated paper-based sensor for copper sensing and solid-state latent fingerprint detection

Recently, researchers have focused on developing a new molecular architecture by integrating rigid and extended pi-conjugation molecules for future applications. Smart functional materials with appealing optical features are essential because of their wide range of applications in sensor and forensic science. A new pyrene-naphthalene-based Schiff base ligand, PSB was developed by a simple condensation method of 2‑hydroxy-1-naphthaldehyde and 1-aminopyrene. The ligand PSB was thoroughly characterized by pivotal techniques such as NMR, FT-IR, HR-MS, and elemental analysis. Paper-based sensors have also been developed for the sensing of Cu2+, which relies on the change in color from yellow to discoloration based on the concentration of Cu2+ in the sample solution. The quantitative determination was executed by calculating the signal intensity of PSB on Whatman filter paper after the addition of Cu2+ using an RGB color detector and smartphone. The calculated LODs from absorption titration and paper-based sensing were 1.7 µM and 2.28 µM, respectively. Moreover, the metal-ligand complex was formed at a 1:1 ratio, which was confirmed by Job's plot, and the binding constant was calculated by the Benesi-Hildebrand plot (5.3 × 104 M−1). The copper complex formation was further confirmed by experimentally and theoretical calculations using Gaussian 09 W software. The prepared PSB is a strong red-emitting fluorescent probe for the identification of latent fingerprints for forensic applications.