Thiourea-based molecular clips for fluorescent discrimination of isomeric dicarboxylates

A new clip-like receptor, which comprises two thiourea-based binding groups and two naphthalene units, has been designed and synthesized as fluorescent chemosensor for distinguishing o-phthalate from two other isomers of dicarboxylates. Upon the addition of these three ions, the emission intensity at 420 nm ( excitation at 340 nm) decreases drastically through PET. When excited at 380 nm, a new emission band at 460 nm appears and develops gradually upon the addition of the o-phthalate ion and the fluorescent intensity increases markedly over time, but the presence of m-phthalate or p-phthalate do not cause this kind of change. It suggests a guest-induced "off-on" conformational switching signaling transduction. The presence of the o-phthalate anion induces a special conformation with two naphthalene units positioned close enough to exhibit a new emission.