Functionalization of Biphenylcarbazole (CBP) with Siloxane-Hybrid Chains for Solvent-Free Liquid Materials

We report herein the synthesis of siloxane-functionalized CBP molecules (4,4′-bis(carbazole)-1,1′-biphenyl) for liquid optoelectronic applications. The room-temperature liquid state is obtained through a convenient functionalization of the molecules with heptamethyltrisiloxane chains via hydrosilylation of alkenyl spacers. The synthesis comprises screening of metal-catalyzed methodologies to introduce alkenyl linkers into carbazoles (Stille and Suzuki Miyaura cross-couplings), incorporate the alkenylcarbazoles to dihalobiphenyls (Ullmann coupling), and finally introduce the siloxane chains. The used conditions allowed the synthesis of the target compounds, despite the high reactivity of the alkenyl moieties bound to π-conjugated systems toward undesired side reactions such as polymerization, isomerization, and hydrogenation. The features of these solvent-free liquid CBP derivatives make them potentially interesting for fluidic optoelectronic applications.

Spectroscopic Evidence of New Low-Dimensional Planar Carbon Allotropes Based on Biphenylene via On-Surface Ullmann Coupling

The bottom-up synthesis and preliminary characterizations of a new biphenylene-based 2D framework are presented. This new low-dimensional carbon allotrope potentially completes the many hypothesized carbon networks based on biphenylene.

Post-functionalization of Ether-linked Polymer via the Application of Ullmann-coupling Reaction: Synthesis, Characterization and Thermal Degradation Kinetics

A new ether-linked polymer (PE-A) was synthesized via the polycondensation of 1,4-dibromo-2,5-difluorobenzene with biphenol (A). The new polymer has shown a good solubility in non-polar solvents, as well as moderate thermal stability (up to 300 °C). The parent PE-A was subjected to post-functionalization modification applying the Ullmann-coupling reaction on the C-Br bonds of PE-A, where the bromo-sites have been replaced by aniline-linked moieties. The resulting polymer (PE-Ani-A) shows slight solubility in several solvents. Its thermal stability was enhanced by 36% when compared with PE-A. To ensure the significant impact of the inclusion of the aniline group on thermal stability, a thermal degradation kinetics study was performed and the Coats-Redfren and Broido theoretical models were applied to explore the degradation process. The calculated activation energy for PE-Ani-A degradation was thereby found to be higher than that of PE-A, which indicates the higher thermal stability of PE-Ani-A. For further insights into the thermal stability of the polymers, the limited oxygen index (LOI), which represents the flame-retardant property of the polymers, was calculated. The results indicate that PE-A is a promising candidate as a flame-retardant polymer (LOI = 46.7), since it has a high bromo-content. On the other hand, PE-Ani-A has a lower LOI although it has a higher thermal stability.

ON-SURFACE MOLECULAR REACTIONS

During the last decades, the bottom–up strategy of on-surface molecular reactions has been extensively investigated in order to fulfill controllable fabrication of covalent interlinking nanostructures/nanomaterials at atomic scale. A variety of organic reactions have been introduced to substrates, such as Ullmann coupling, Glaser coupling, cyclodehydrogenation and so on. In this paper, these on-surface molecular reactions will be reviewed from three aspects: the precursor, surface and external stimuli. Finally, a summary of past achievements and an outlook of future scientific challenges will be discussed.