A “breathing” dendritic molecule—conformational fluctuation induced by external stimuli

A series of PAMAM dendrimers peripherally modified with tetraphenylethylene (TPE), a typical chromophore with emission enhancement in aggregate, were synthesized (D0–D4). The dendrimers are molecularly dissolved in toluene, a selective solvent. The intramolecular rotation of TPE is depressed by the restrained conformation caused by the congested packing periphery in higher generation dendrimers (D2–D4), which results in a remarkable emission enhancement. The fluorescence quantum yield increases more than 10-fold in D3 and D4 dendrimers compared with a model compound. Furthermore, the emission intensity of dendrimers can be tuned by changing the temperature or solvent conditions, which alters the conformational confinement. Unimolecular spheres with multiple chromophores and conformation-controlled emission are reminiscent of proteins with modulated sizes and photofunctions. Developing these dendritic systems will promote the research of multi-functionalized chromophores and lead to their potential applications in biomimics and sensors.