Progress in fluorene-based wide-bandgap steric semiconductors

Emission Enhanced and Stabilized by Stereoisomeric Strategy in Hierarchical Uniform Supramolecular Framework

“…Molecular orientation and anisotropy may induce long effective conjugation length, resulting in a range of extra absorbance peaks at longer wavelengths and an overall redshift of the PL spectrum (Figures 2, S11, and S12). 35,36 A new absorption shoulder, lower in energy than the p-p* transition, is the dominant feature associated with the formation of oriented planar conjugated backbone structures (Figure 2A). This high molecular orientation also produces profound changes in the photophysical behaviors because of the longer conjugation and increased effective p-electron delocalization.…”

Hereditary Character of Alkyl-Chain Length Effect on β-Phase Conformation from Polydialkylfluorenes to Bulky Polydiarylfluorenes

“…Their long-range and short-range conformations of polymer chains give rise to their polymorphism, offering a versatile library to optimize device performance. − Polymorphism involves networks of complex noncovalent bonding among the polymer chains, related to the conformation change, deformation, steric strains, as well as chain entanglement from solution to film under the nonequilibrium external conditions; this makes the manipulation of PFs polymorphism become extremely challenging. − Among the various morphologies of PFs, the β-phase exhibits several merits over the amorphous state, such as efficient light-emission, charge carrier mobility, and amplified spontaneous emission. − The alkyl-chain length effect has been demonstrated in polydialkylfluorenes (PF n , n = 6, 7, 8, 9) comprehensively, for example, the octyl chain was the most favorable length to induce β-phase, and different intrachain torsional angles have corresponding unit cells in their thin film states. − However, green-band emission of PFs is detrimental to the efficiency and color purity of PLEDs. − Steric groups have been incorporated into PFs to effectively avoid green-band emission, as well as the ladder-type PFs modified with aryl groups. − However, these strategies either impeded the formation of β-phase or were limited by difficult synthesis. According to supramolecular steric hindrance effect (SSH), we obtained β-phase in a polydiarylfluorene recently, which exhibited not only a high fluorescent efficiency and excellent stability by thermal annealing but also a superior crystallinity among the sterically hindered PFs. − …”

Crystalization-enhanced Stability by Effectively Suppressing Pho-tooxidation Defect for Lasing Emission and Electroluminescent Device

“…20 Since 1990s ~ 2000s, uorene-based building blocks have been indispensable candidates in OWBGSbased systems and photoelectronic devices. 21,22 Generally, amorphous molecules with high glassy transition temperature (Tg) serve as the stable active layers, where molecular arrangements are disordered and loose. In this case, the generation of massive defects from the O 2 /O.…”