Preparation and property manipulation of high efficiency circularly polarized luminescent liquid crystal polypeptides

Abstract

Circularly polarized luminescent (CPL) materials show great potential applications in asymmetric synthesis, chemical sensors, biological probes, 3D displays and other fields. However, the preparation of high efficiency circularly polarized luminescent materials with a high solid fluorescence quantum yield and a large g_lum value is still a challenge. This article creatively combines the construction strategy of CPL materials and side-chain chiral liquid crystal polymer materials to engineer a series of new CPL-active side-chain chiral liquid crystal polymers (named PGAC-m, m is the spacer length, m = 4, 6, 10). The chiral poly(L-glutamate) with an α-helical secondary structure is devised as the backbone, and the cyanostilbene with aggregation-induced emission enhancement (AIEE) characteristics is applied as luminescent mesogen pendants, which is covalently linked to the backbone by different spacer lengths. The phase structure and the photophysical properties of PGAC-m were characterized in detail. The experimental results show that PGAC-m can self-assemble to form a lamellar-ordered chiral smectic C (SmC*) phase structure and show typical AIEE characteristics with high solid-state quantum yield. The chirality of polypeptides can be transferred to cyanostilbene, which makes PGAC-m emit circularly polarized light. Meanwhile, the chiral helix structure of PGAC-m can effectively enlarge the g_lum value, and therefore PGAC-m shows high solid quantum yield and a large g_lum value. Interestingly, the photophysical properties of PGAC-m can be regulated by changing the spacer length. The solid fluorescence quantum yield of PGAC-m decreases gradually with the increase of spacer length, while the g_lum value shows the opposite trend. The maximum solid fluorescence quantum yield and the g_lum value of PGAC-m can be 34.1% and 4.5 × 10⁻², respectively.