Self-assembly solid-state enhanced red emission of quinolinemalononitrile: optical waveguides and stimuli response

The fluorescence of luminescent emitters is often quenched in the solid state, because of the typical aggregation-caused quenching (ACQ) effect, which is a thorny obstacle to high-performance organic optoelectronic materials. The exploration of solid-state enhanced long wavelength, red-emitting chromophores, especially possessing one-dimensional (1D) assembly features, is of great importance. Interestingly, an excellent solid-state enhanced red emission system (denoted as ED) based on quinolinemalononitrile has been developed via the delicate modification of the conventional ACQ dicyanomethylene-4H-pyran (DCM) derivative (denoted as BD) through crystal engineering. ED exhibits extraordinary self-assembly property in a variety of solvents, even realizing the "waving ribbons" with a length of 6 mm and a diameter of 10 μm. Crystal analysis shows that the CH···π and CH···N supramolecular interactions of ED contribute to the twisted self-assembly solid-state enhanced emission phenomenon. However, for BD, strong face-to-face stacking leads to fluorescence quenching in the solid state. Because of such easy assembly and strong solid-state emission properties, application for optical waveguides of ED is realized with a low optical loss. Stimuli-responsive behavior is also elaborated with color change between orange and red by grinding/fuming or pressing/heating.