Rational molecular design allows for manipulating the chain conformations of polymer semiconductors by cooperative arrangement of bulky groups with steric hindrance effect and supramolecular groups with noncovalent attractions. Herein, a model polyfluorene with β-phase, poly[4-(octyloxy)-9,9-diphenylfluoren-2,7-diyl]-co-[5-(octyloxy)-9,9-diphenylfluoren-2,7-diyl] (PODPF), has been synthesized successfully via key Baeyer–Villiger rearrangement reaction. Its thin film exhibited excellent spectral stability without green band emission after thermal annealing at 200 °C under air and nitrogen ambients. The β-phases of PODPF in the concentrated toluene solution, organogels, and films have been characterized and confirmed by UV absorption and PL spectra as well as grazing-incidence X-ray scattering. The results suggest that the octyloxy substituents enable backbone planarization via van der Waals forces of the in-plane alkyl chains to overcome intrachain repulsion between fluorene monomers. Organic lasers using β-phase PODPF exhibit lower threshold than those of poly(9,9-dioctylfluorene), suggesting promising optical gain media. This observation suggested that supramolecular steric hindrance (SSH) is a promising molecular design of polymer semiconductors, and supramolecular steric polymers are one kind of model to get insight into the structure–function relationships for electrically pumped organic lasers in organic electronic and photonics.

Bulky conjugated polymers with high crystallinity is the prerequisite for the overall improvement of performance in wide-bandgap semiconductors, including charge transport, photoluminescence quantum yield, processing reliability, and stability. Herein, we report a stable β-phase film of bulky polydiarylfluorene (PODPF) preparing by thermal annealing at ∼220 °C. The β-phase conformation and regular molecular packing are confirmed by UV-vis, photoluminescence (PL), Raman spectra, and grazing incidence X-ray diffraction (GIXD), respectively. Polymer light-emitting diodes (PLEDs) with crystalline and β-phase film serving as the active layer exhibit higher current efficiency of 1.8 cd/A (6.0 V) and more stable electroluminescence over the amorphous one. Surprisingly, mixed conformations in PODPF film produce dually tunable amplified spontaneous emission (ASE) at 463 and 482 nm. Polydiarylfluorenes with quasi-planar conformation will be a promising candidate for the next-generation gain medium toward a broadly tunable lasing and dual-wavelength laser.

Scheme 1. Schematic representation of the supramolecular self-encapsulation strategy for wide-bandgap LCPs. A) Typical molecular model of our supramolecular self-encapsulated LCPs (SMART: Synergistically Molecular Attractor-Repulsor Theory). B) Chemical structures of the model polymer, PHDPF-Cz, together with the controlled polyfluorenes. C) Computer-generated model of PHDPF-Cz: i) axial and ii) lateral views. Schematic diagram illustrating the ideal molecular packing model for a PHDPF-Cz self-assembled superstructure, where the pendent Cz groups self-assemble into a sheath and act as an encapsulated layer to isolate the chain and inhibit the interchain interaction between π-π backbones, similar to previous studies. [47,52,53] The blue rings signify the backbone chain. The red loops indicate the Cz-threaded layers. The yellow arrow represents the 2D charge transport channel. The orange-yellow arrow denotes the penetration path for various gases, which is disrupted by the Cz-threaded layer.

During the past decades, π-conjugated polymers have been studied intensively owing to their potential applications in organic optoelectronic devices, such as polymeric light-emitting diodes, bulk heterojunction solar cells, organic field-effect transistors (OFETs), organic memories, biosensors, and actuators. 1,2 The performance of organic devices is determined not only by the inherent electronic structures of individual polymer chain 3,4 but also by multiscale morphologies that were constructed by the drive of supramolecular interactions or van der Waals' forces. Many efforts have been made to design the controllable welldefined nanostructures or hierarchically ordered assemblies in the field of supramolecular semiconductors and electronics for the high-performance or new functional devices. 5,6 One typical example is that ordered self-organization of polythiophenes dramatically influences the performance of bulk heterojunction photovoltaic cells as well as the mobility of OFETs. 7,8 Lightemitting polyfluorenes (PFs) is another impressive example of polymorphisms, including amorphous phase, semicrystalline (R-) phase and R 0 -phase, β-phase, and nematic liquid crystalline (N-) phase. These abundant phases provide a unique opportunity to study the relationship between phase morphology and device performances. 9-13 For example, PFO thin film containing the β-phase exhibits the excellent spectral stability in PLEDs and the pumped lasers with low threshold. 14-16 In this context, it is of the utmost importance to explore further the unique morphology and phase of π-conjugated polymers, which are based on its unique self-assembly mode and supramolecular interactions. Supramolecular gel is a fascinating state that appears solid-like and yet is composed predominantly of a liquid and a small amount of gelators stabilized by supramolecular interactions with 3D networks. 17-20 Until now, low-molecular-mass organogels (LMOGs) have been applied in a wide range of fields, such as biomimetics, separations, drug delivery, soft templates, and tissue engineering. 21-24 Steroid or lipid units have served as gelators to generate cross-linking points in the 3D networks. 25 In addition, some electronically inactive comb-shaped polymers (isotactic and syndiotactic polystyrene (PS), 26 poly(methyl methacrylate), 27 and polyesters 28 ) have also been found to form gel networks easily owing to their unique helical conformations. However, little attention has been paid to π-conjugated polymers. 29-32 Supramolecular π-conjugated polymer gels (SCPGs) can be served as one kind of semiconducting soft materials with distinguished porous structures that may find applications in nanosensors, 33 mimic-artificial muscle, 34 super capacitor, 35 and lithium battery material. 36 Poly(3-alkylthiophene)-based gels were prepared by quenching xylene solution at 150°C, and its conductivity was improved. 37,38 ABSTRACT: Supramolecular π-conjugated polymer-based gels (SCPGs) are one important kind of semiconducting soft materials. Herein we demonstrate a p...