Blue fluorescent emitter based on HLCT and AIE: acidichromism behaviors and narrow-band emission in OLEDs application

Abstract

Due to the low cost, less toxicity, and high exciton utilization, fluorescent emitters based on the hybridized local and charge-transfer (HLCT), namely “hot exciton”, as potential organic light-emitting diodes (OLEDs) materials have attracted significant interest. However, because the pure blue emitters possess wide energy gap and π-π molecular stacking effects, developing blue efficient and narrow full width at half maximum (FWHM) fluorescence material is still a challenge. Herein, a blue fluorescent emitter (CF3-PPI-TPE) was successfully designed and synthesized by incorporating aggregation-induced emission (AIE) unit of tetraphenylethylene (TPE) and HLCT unit of phenanthroimidazole (PPI). The HLCT excited state and AIE properties of CF3-PPI-TPE were proved by photophysical measurements and time-density functional theory (TD-DFT) calculation. In addition, CF3-PPI-TPE exhibited obvious acidichromism behaviors with the color change from blue to green after fuming with trifluoroacetic acid (TFA), and the color change was reversible after treatment with NH3 gas. The non-doped (device I) and doped (as host, device II; as guest, device III) OLEDs features based on CF3-PPI-TPE have been explored. The three devices color CIE coordinates are (0.126, 0.099), (0.135, 0.051) and (0.135, 0.061), and the FWHM of in OLEDs are 22.2 nm, 17.3 nm and 22.9 nm, respectively. Addition, their Commission Internationale de L'Eclairage (CIEy) are less than 0.07 in OLEDs. These results provide a new strategy for developing narrow FWHM for OLEDs and stimuli-responsive materials based on AIE and HLCT effects.