Color-Tunable and Stimulus-Responsive Luminescent Liquid Crystalline Polymers Fabricated by Hydrogen Bonding

Luminescent liquid crystalline polymers (LLCPs) show extensive application potentials, such as liquid crystal displays and circularly polarized luminescence. In this work, we employ a hydrogen-bonding strategy different from the traditional covalent-bonding method to fabricate LLCPs. First, the acceptor and donor of hydrogen bonding, (4,4'-dibutanoxy tetraphenylethylene)-1-pyridine (PTPEC₄) and poly(2-vinyl terephthalic acid) (PPA), respectively, are successfully synthesized. Then, mixtures with different molar ratios ( x's) of PTPEC₄ to PPA are used to prepare a series of LLCPs [denoted as PPA(PTPEC₄) _x]. The resultant LLCPs show a smectic A phase ( x ≥ 0.8), a columnar nematic phase (0.6 ≤ x ≤ 0.05), and an amorphous state ( x = 0.025), depending on the x value. Meanwhile, all polymers exhibit typical aggregation-induced emission behavior. More interestingly, with the variation of the PTPEC₄ content, the series of LLCPs show different colors, that is, the emission peak red shifts from 510 nm ( x = 1.0) to 551 nm ( x = 0.025). Furthermore, because of the reversible protonation effect of the N atom of pyridine in PTPEC₄ by the strong proton acid, PPA(PTPEC₄) _x shows reversible color transformation. This work provides a new method to construct LLCPs with different emission colors and reversible color transformation.