A naphthalene exciplex based Al3+ selective on-type fluorescent probe for living cells at the physiological pH range: experimental and computational studies

2-((Naphthalen-6-yl)methylthio)ethanol (HL) was prepared by one pot synthesis using 2-mercaptoethanol and 2-bromomethylnaphthalene. It was found to be a highly selective fluorescent sensor for Al3+ in the physiological pH (pH 7.0-8.0). It could sense Al3+ bound to cells through fluorescence microscopy. Metal ions like Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Ag+, Cd2+, Hg2+, Cr3+ and Pb2+ did not interfere. No interference was also observed with anions like Cl-, Br-, F-, SO42-, NO3-, CO32-, HPO42- and SCN-. Experimentally observed structural and spectroscopic features of HL and its Al3+ complex have been substantiated by computational calculations using density functional theory (DFT) and time dependent density functional theory (TDDFT).