Aggregation induction of tetraphenylethylene AIEgen and its supramolecular aggregates toward light-emitting diodes

Aggregation behavior of luminophores is a subject of great interest over more than half a century. Aggregation generally causes quenching of luminescence of luminophores, which is detrimental for the solid state electroluminescence device fabrication. In oppose to the aggregation caused quenching, aggregation-induced emission phenomenon leads to highly luminescence state of luminophores upon aggregate formation. However, aggregation-induced emission behavior of the luminophores is commonly observed in irregular bulk solids, by adding antisolvents into a solution or in the biological cells, where the state of aggregation remains uncontrolled. Here we report on the synthesis of a new tailor made luminogen, 4′,4‴-(2,2-bis(4-methoxyphenyl)ethene-1,1-diyl)bis([1,1′-biphenyl]-4-carbaldehyde) (TPE 2) using Suzuki coupling reaction with high yield. We form the well-controlled supramolecular aggregates of TPE 2 ​at the air−water interface of a Langmuir trough. As a consequence, the mono- and multilayer Langmuir−Blodgett films of TPE 2 show a large enhancement of luminescence in comparison to the solution phase owing to the aggregation-induced emission phenomenon. We reveal inherent interaction of TPE 2 complexes within the supramolecular aggregates using density functional theory. This unique feature of luminescence enhancement is utilized for the fabrication of light-emitting diodes with low threshold voltage using TPE 2 as active layer. This study opens up the advantage of ordered supramolecular assembly to achieve optimal luminescence performances.