Synthetic Concept of Intrinsically Elastic Luminescent Polyfluorene-Based Copolymers via RAFT Polymerization

Abstract

An easy and novel synthetic concept for building intrinsically stretchable and elastic semiconducting polymers is designed in this study, in which a conjugated rod−coil block copolymer with a rigid poly(9,9-di-n-octyl-2,7-fluorene) (PFO)conjugated rod and soft poly(isoprene) (PI) coils were utilized as model compounds for demonstration. By combining a coupling reaction for a conjugated block and reversible addition− fragmentation chain transfer for a functional soft block, a simplified synthetic procedure for semiconducting polymers incorporating different lengths of the PI moiety, PF-b-(PI) x (x = 0.9, 1.2, and 1.8), was thus developed. Upon intense mechanical stress, both their stretching and rubbery properties associated with highly stable luminescence were demonstrated because of the molecular-level rigid island structure of self-assembly nanostructured PF domains bridged by PI segments. In particular, the PF-b-PI 1.8 thin film could not only be stretched by up to 150% without forming any cracks but also be employed for the fabrication of free-standing films with both excellent elasticity and tough mechanical strength after cross-linking, showing high stability in quantum yield over 1000 stretching cycles at 150% strain.

Intrinsically flexible displays: key materials and devices

“…Copyright 2022, John Wiley and Sons. (g) Molecular structure of the stretchable PF-b-PI copolymer [ 78 ]. Copyright 2020, American Chemical Society.…”

“…(h) Schematic illustration of the deformable polymer with a PF-b-PI 1.8 matrix and cross-linker 1, 9-nonanedithiol (DT). Blue-rectangular block, pink fibril and gray sphere denote the PF rod, PI coil and the cross-linked point, respectively [ 78 ]. Copyright 2020, American Chemical Society.…”

“…Copyright 2020, American Chemical Society. (i) Photographic images of the cross-linked stretchable PF-b-PI 1.8 film at a strain of 0% and 300% [ 78 ]. Copyright 2020, American Chemical Society.…”

“…In addition to the doping strategy, copolymerization is another effective approach to designing intrinsically flexible OESCs. Rigid rods connected with elastomeric coils facilitate polymer rigid island-soft bridge stacking, ensuring improved stretchability and optoelectronic properties [ 78 ]. Jao et al .…”

“…The elastomeric spacer lent good stretchability to the emissive polymer, but sacrificed charge transfer efficiency. A similar strategy was used by Au-Duong et al ., where a rigid poly (9,9-di-n-octyl-2,7-fluorene) (PFO)-conjugated rod and soft poly (isoprene) (PI) coils were connected to obtain PF-b-(PI)x [ 78 ]. The obtained PF-b-PI 1.8 could sustain 150% strain over 1000 stretching cycles without losing its photoluminescence quantum yield (PLQY) (Fig.…”