Acceptor Copolymerized Axially Chiral Conjugated Polymers with TADF Properties for Efficient Circularly Polarized Electroluminescence

Abstract Chiral conjugated polymer has promoted the development of the efficient circularly polarized electroluminescence (CPEL) device, nevertheless, it remains a challenge to develop chiral polymers with high electroluminescence performance. Herein, by the acceptor copolymerization of axially chiral biphenyl emitting skeleton and benzophenone, a pair of axially chiral conjugated polymers namely R‐PAC and S‐PAC are synthesized. The target polymers exhibit obvious thermally activated delayed fluorescence (TADF) activities with high photoluminescence quantum yields of 81%. Moreover, the chiral polymers display significant circularly polarized luminescence features, with luminescence dissymmetry factor (|g lum|) of nearly 3 × 10−3. By using the chiral polymers as emitters, the corresponding circularly polarized organic light‐emitting diodes (CP‐OLEDs) exhibit efficient CPEL signals with electroluminescence dissymmetry factor |g EL| of 3.4 × 10−3 and high maximum external quantum efficiency (EQEmax) of 17.8%. Notably, considering both EQEmax and |g EL| comprehensively, the device performance of R‐PAC and S‐PAC is the best among all the reported CP‐OLEDs with chiral conjugated polymers as emitters. This work provides a facile approach to constructing chiral conjugated TADF polymers and discloses the potential of axially chiral conjugated luminescent skeletons in architecting high‐performance CP‐OLEDs.


General Information
All reagents were purchased from commercial providers without further purification. 1H NMR and 13 C NMR spectra were recorded on AVIII 500 MHz NMR spectrometers in CDCl3 solutions.High-resolution mass spectra were measured on a Thermo Fisher® Exactive high resolution LC-MS spectrometer.HPLC analysis were performed on Agilent 1260 Infinity.
Analytical injections were performed on chiral stationary phase using the column (Chiralpak® ID, 4.6 mm × 150 mm) and the mobile phase of methanol.Single crystal data was obtained on a Bruker Smart APEXII CCD diffractometer using graphite monochromated Cu Kα radiation.
The average weights of the polymers were measured by gel permeation chromatography (GPC) on Waters 410 using polystyrene as standard and THF eluent.The thermogravimetric analysis (TGA) and differential scanning calorimetric (DSC) measurement were respectively performed on Q600 thermogravimeter and Q2000 simultaneous thermal analyzer at a heating rate of 10 °C min -1 in nitrogen.Cyclic voltammetry was performed using a CHI600A analyzer with a scan rate of 100 mV/s at room temperature.A conventional three electrode cell was used as electrolytic cell with a glassy carbon working electrode, Pt wire as the counter electrode, and an Ag/Ag + (0.01 M AgNO3) as the reference electrode.The oxidation potential was measured in dichloromethane with 0.1 M of tetra-n-butylammonium hexafluorophosphate (n-Bu4NPF6) as a supporting electrolyte.Ferrocene used as internal standard for calibrating the reference electrode.
The repetitive unit structure of the chiral polymer was optimized with dispersion corrected density functional theory (DFT-D3) at the B3LYP-D3(BJ)/6-31G(d) level using Gaussian 09 S1] The energy levels of excited states were calculated at the B3LYP-D3(BJ)/6-31G(d) level with the time-dependent density functional theory (TD-DFT) method.The natural transition orbits (NTOs) were calculated through TD-DFT method and the Multiwfn 3.8 program was used to analyze the characteristics of excited states.The spin-orbit coupling (SOC) matrix elements were calculated using the spin-orbit mean-field (SOME) methods based on the excited state wave functions obtained from TD-DFT calculations.All these calculations were performed utilizing ORCA 5.0.4 program.S2] UV-Vis spectra were recorded on PerkinElmer® UV/Vis/NIR spectrometer (Lambda 950).
The photoluminescence spectra and transient PL decay characteristics were measured on an Edinburgh Instruments FLS 1000 spectrometer.The absolute photoluminescence quantum yield (PLQY) was measured on the FLS 1000 spectrometer using an integrating sphere at an excitation wavelength of 340 nm.The circular dichroism (CD) spectra were recorded on a JASCO J810 spectropolarimeter.The circularly polarized photoluminescence (CPL) and circularly polarized electroluminescence (CPEL) measurements were performed utilizing a commercialized instrument JASCO CPL-300 spectrophotometer at room temperature.

Figure S5 .
Figure S5.HPLC profile of R-ACBr after heating to 100º C.

Figure S6 .
Figure S6.HPLC profile of S-ACBr after heating to 100º C.

Figure S26 .
Figure S26.The glum values versus wavelength curves of R/S-PAC and R/S-ACBr in toluene solution (c = 10 -5 M) at 298 K.

Table S1 .
Crystal data and structure refinement for R-ACBr.

Table S2 .
Crystal data and structure refinement for S-ACBr.

Table S3 .
The summary of HPLC profiles of rac-ACBr and R/S-ACBr.