Achiral dynamic helical polymers, poly(quinoxaline-2,3-diyl)s (P1 and P2) bearing achiral carboxylic acid side chains, i.e., carboxymethoxymethyl (in P1) and carboxyethoxymethyl (in P2), with different polymerization degrees were synthesized. They exhibited induced circular dichroism (ICD) in the presence of chiral amines such as 1-phenylethylamine and nicotine, 1,2-amino alcohols such as valinol, leucinol, and prolinol, and the basic amino acid, arginine, in response to the induction of right- or left-handed helical conformation. The efficiency of helix induction depends on the compatibility of the structures of amines and polymers, with no clear structural correlation. The highly sensitive and formulated nature of ICD with the helical polymer-based poly(carboxylic acid)s allowed their use as CD-based sensors to detect and quantify minute imbalances of the enantiomeric excess of chiral molecules. We determined 0.2%-0.6% ee in the commercially available 1-phenylethylamine from three different suppliers, which have the label of "dl" or no indication of enantiopurity using P1 as a chemosensor.
N-(o-Cyanophenyl)carbazole can be dimerized at different positions, which may change excited state behaviors. Herein, 2,3'-dicyano-3,4'-di(carbazol-9-yl)biphenyl (D34C) is designed and synthesized and doped into polymers. However, we find that D34C does not exhibit room temperature phosphorescence but emits fluorescence (FL) and bright thermally activated delayed fluorescence (TADF) with lifetimes of hundreds of milliseconds, which is observed in diverse matrices such as PMMA, MBS, ABS, PS, HIPS, and SIS. The simple positional isomerization makes the abundant triplet excitons undergo only reverse intersystem crossing rather than room temperature phosphorescence (RTP) radiation, which is rather rare in organic doped polymers. Since the production of TADF afterglow requires a certain excitation time, the generally indistinguishable FL and TADF efficiencies are separated for the first time. This work not only provides novel TADF afterglow polymers with diverse mechanical properties but also will evoke the subtle design of conjugated organic molecules to dramatically change photoexcitation and emission behaviors.
A blend of high-density polyethylene (HDPE, Mw = 59.4 kDa) and stearic acid was efficiently degraded under cerium catalyzed photodecarboxylation conditions, and the molecular weight decreased to Mw = ∼5 kDa. The reaction proceeds at 100 °C in tert-butylnitrile (tBuCN) in air, where HDPE does not dissolve or swell. The products are solid material with >90% weight recovery of the starting HDPE + stearic acid. Control experiments supported that carbon radicals generated by cerium-catalyzed photodecarboxylation of stearic acid transferred to the main chain of the HDPE, which undergoes oxidative degradation to lower the molecular weight.