Synthesis of calix[4]arenes bearing thiosemicarbazone moieties with naphthalene groups: Highly selective turn off/on fluorescent sensor for Cu(II) recognition

•Calix[4]arene bearing thiosemicarbazone with naphthalene groups were synthesized.•L1 and L2 recognize selectivity Cu2+ in presence of cations and anions.•L2 conformation change from cone to pinched cone in presence of copper.•L2 has a detection limit of 1.58 ppb for Cu2+ in acetonitrile.