Tetraphenylcyclopentadiene Derivatives: Aggregation-Induced Emission, Adjustable Luminescence from Green to Blue, Efficient Undoped OLED Performance and Good Mechanochromic Properties

Silole derivatives, the first reported and famous AIEgens, are a series of Si-containing conjugated rings with the sigma*-pi* conjugation, and this unique electronic structure imparts them high electron affinity and fast electron mobility, but not ideal blue luminogens due to their relatively long conjugation length. By replacing the Si atom with the C one, six new AIEgens without the sigma*-pi* conjugation effect are successfully synthesized based on a tetraphenylcyclopentadiene core. In addition to the skyblue emission (lambda(EL) = 492 nm) with L-max, eta(C,max), and eta(P,max) up to 24 096 cd m(-2), 6.80 cd A(-1), and 4.07 lm W-1, respectively, the careful control of the conjugation degree by changing the linkage mode, results in the blue one (lambda(EL) = 440 nm) with relatively good performance (L-max: 8721 cd m(-2) and eta(C,max): 3.40 cd A(-1)), indicating that the replacement of the Si atom by C one is an alternative design strategy to yield blue even deep-blue AIEgens with good device performance. Meanwhile, their reversible mechanochromic properties are realized with apparent fluorescence changes between deep-blue and green emissive colors, offering them additional promising applications in optoelectronic devices.