Liquid Crystalline Fluorene-2,1,3-Benzothiadiazole Oligomers with Amplified Spontaneous Emission

Conjugated fluorene-based molecules are a powerful class of materials for optoelectronic applications, known for their outstanding photoluminescence quantum yields and easily tunable optical properties. While conjugated polymers like poly(fluorene-co-benzothiadiazole) have been extensively studied, their performance is often hindered by product inhomogeneity and morphological constraints. By contrast, well-defined oligofluorenes offer precise molecular structures and better morphological control, making them an attractive alternative to conjugated polymers. Among them, benzothiadiazole (BT)-centered oligofluorenes exhibit strong yellow emission with remarkably high photoluminescence quantum yields, yet their morphological properties remain largely unexplored. In this study, a straightforward synthesis of BT-cored pentafluorenes is reported, where the alkyl side chains are systematically varied to investigate their impact on the morphology. These pentamers demonstrate amplified spontaneous emission (ASE) with thresholds as low as 1.64 µJ cm⁻2. By fine-tuning the alkyl chains, crystalline, amorphous, and liquid crystalline morphologies are achieved, while maintaining consistent optical properties, paving the way for defined materials in advanced optoelectronic applications.

Correlation between the Molecular Properties of Semiconducting Polymers of Intrinsic Microporosity and Their Photocatalytic Hydrogen Production

Increasing the interface area between organic semiconductor photocatalysts and electrolyte by fabricating nanoparticles has proven to be an effective strategy to increase photocatalytic hydrogen production activity. However, it remains unclear if increasing the internal interface by the introduction of porosity has as clear benefits for activity. To better inform future photocatalyst design, a series of polymers of intrinsic microporosity (PIMs) with the same conjugated backbone were synthesized as a platform to independently modulate the variables of porosity and relative hydrophilicity through the use of hydrophilic alcohol moieties protected by silyl ether protecting groups. When tested in the presence of ascorbic acid and photodeposited Pt, a strong correlation between the wettable porosity and photocatalytic activity was found, with the more wettable analogue of two polymers of almost the same surface area delivering 7.3 times greater activity, while controlling for other variables. Transient absorption spectroscopic (TAS) investigation showed efficient intrinsic charge generation within 10 ps in two of the porous polymers, even without the presence of ascorbic acid or Pt. Detectable hole polarons were found to be immediately extracted by added ascorbic acid, suggesting the generation of reactive charges at regions readily accessible to electrolyte in the porous structures. This study directs organic semiconductor photocatalysts design toward more hydrophilic functionality for addressing exciton and charge recombination bottlenecks and clearly demonstrates the advantages of wettable porosity as a design principle.

Dihydroindenofluorenes as building units in organic semiconductors for organic electronics

This review aims to discuss organic semiconductors constructed on dihydroindenofluorene positional isomers, which are key molecular scaffolds in organic electronics. Bridged oligophenylenes are key organic semiconductors that have allowed the development of organic electronic technologies. Dihydroindenofluorenes (DHIFs) belong to the family of bridged oligophenylenes constructed on a terphenyl backbone. They have proven to be very promising building blocks for the construction of highly efficient organic semiconductors for all OE devices, namely organic light emitting diodes (OLEDs), phosphorescent OLEDs, organic field-effect transistors (OFETs), solar cells, etc.

Rigidly Fused Spiro-Conjugated π-Systems

Spiro-fused π-systems have gained considerable attention for their application as semiconductors in molecular electronics. Here, a synopsis regarding recent breakthroughs in ladderized spirobifluorenes and indeno-spirobifluorenes, along with further spiro-condensed heteroatomic hydrocarbons with donor-acceptor moieties, is provided. Additionally, an extended range of rigid spirobifluorene polymers and specific doubly linked spiro-systems with partial chiral character is discussed. The diverse applications of the aforementioned structures are thoroughly evaluated.