Aggregation-induced emission enhancement of phosphaphenanthrene-containing p-phenylene dibenzoate and its application to detecting transition metal ions

Fluorescence of the organic light-emitting compounds is often quenched when the luminophors are fabricated into solid thin films, which has greatly limited their scope of practical applications. So, it is important to design and synthesize the novel organic luminophors with excellent light emission property in the solid state. When 6-oxa-5-oxo-5-[2,5-di(benzoyloxyphenyl)]-5-phosphaphenanthrene (OP) aggregates to a certain degree, the fluorescence strength of OP increases proportionably, which shows obvious aggregation- induced emission enhancement (AIEE) property because the aggregation state of OP restricts rotation of the phosphaphenanthrene groups based on π-π stacking and polarity interaction between the molecules. The experimental result indicates that the concentration of OP influences AIEE property. If OP concentration was lower than 1 × 10^-6 mol·L^-1, AIEE property disappeared. Hg²⁺, Fe₂+and Fe³⁺ ions (1 × 10^-4 mol· L^-1) can efficiently quench the emission intensity of OP (2 × 10^-5 mol·L^-1) during the aggregation state formation, with the quenching efficiency to OP fluorescence being 26%, 34%, 74%, respectively and higher than those by Pb²⁺, Zn²⁺, Cd²⁺, Co²⁺, Mn²⁺, Cu²⁺, Ni₂₊ and Ag₊ ions. This novel phenomenon may enable the molecule to find applications to discriminating chemosensors to detect the transition metal ions.