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 a 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.