Alkoxy chain regulated stimuli-responsive AIE luminogens based on tetraphenylethylene substituted phenanthroimidazole derivatives and non-doped OLEDs with negligible efficiency roll-off
TThree novel tetraphenylethylene derivatives with different length of alkoxy chain, named TPEO1-PPI, TPEO4-PPI and TPEO6-PPI, are synthesized and fully characterized. All of them show obvious aggregation-induced emission (AIE) properties with high photoluminescence quantum yield (PLQY) in film state. The synthesized emitters exhibit green or blue emission in solid state, a significant blue-shift is observed in emission spectra upon increasing the length of alkoxy chains. Interestingly, all these compounds demonstrate mechanofluorochromic (MFC) properties with a significant red-shifted after mechanical grinding. X-ray diffraction results indicate that the MFC property can be attributed to morphological transition from crystalline to amorphous. Due to the high PLQY in film states and matched energy levels , the device based on TPEO4-PPI, showing outstanding maximun luminance (up to 15995 cd m−2 at 8.7 V), remarkable electroluminescence (EL) eﬃciencies (4.51 lm W−1 and 4.22 cd A−1) and maximum external quantum efficiency (EQE) of 4.07%. In addition, these devices show small eﬃciency roll-oﬀ, the corresponding EQE remained at 3.59% at a high luminance of 1000 cd m-2. These results indicate the length of the peripheral alkoxy chains connected to the terminal group can have great influence on the photophysical properties, which deserves attention in molecular design.