Towards the Bisbenzothienocarbazole Core: A Route of Sulfurated Carbazole Derivatives with Assorted Optoelectronic Properties and Applications

Programming Positive Mechanofluorescence in Liquid Crystalline Elastomers

Liquid single crystal elastomers (LSCEs) containing organic fluorophores within their polymeric network are attractive materials to detect forces with simple spectroscopic measurements. Hitherto, all mechanoluminescent LSCEs decrease their emission intensity upon mechanical stimulation; that is, they display negative mechanofluorescence. Such behavior is governed by the mechanically induced approximation of the quenching mesogenic units and the fluorophores. In this work, we propose the integration of fluorescent molecular rotors (FMRs), whose luminescence is not quenched by the mesogens, in LSCEs as a valuable strategy to conceive elastomeric materials programmed with exactly the opposite behavior, i.e., their fluorescence increases upon deformation (positive mechanofluorescence). Specifically, carbazole-indolenine dyes are interesting candidates for this purpose since their luminescence depends mainly on the degree of intramolecular rotation allowed by the local environment. On this basis, the uniaxial deformation of an LSCE, along its anisotropic direction, incorporating such FMRs will place the fluorophores in a more restricted medium, leading to the desired enhanced emission at the macroscale.

Powder X-ray diffraction as a powerful tool to exploit in organic electronics: shedding light on the first N,N',N''-trialkyldiindolocarbazole

The first crystal structure of a fully N-alkylated diindolocarbazole derivative, namely, 5,8,14-tributyldiindolo[3,2-b;2',3'-h]carbazole (1, C₃₆H₃₉N₃), has been determined from laboratory powder X-ray diffraction (PXRD) data. A complex trigonal structure with a high-volume unit cell of 12987 ų was found, with a very long a(=b) [52.8790 (14) Å] and a very short c [5.36308 (13) Å] unit-cell parameter (hexagonal setting). The detailed analysis of the intermolecular interactions observed in the crystal structure of 1 highlights its potential towards the implementation of this core as a semiconductor in organic thin-film transistor (OTFT) devices. Since the molecule has a flat configuration reflecting its π-conjugated system, neighbouring molecules are found to stack atop each other in a slipped parallel fashion via π-π stacking interactions between planes of ca 3.30 Å, with a centroid-centroid distance between the aromatic rings corresponding to the shortest axis of the unit cell (i.e. c). The alkylation of the three N atoms proves to be a decisive feature since it favours the presence of C-H...π interactions in all directions, which strengthens the crystal packing. As a whole, PXRD proves to be a valuable option for the resolution of otherwise inaccessible organic crystal structures of interest in different areas.

Synthesis and Effect of the Structure of Bithienyl-Terminated Surfactants for Dielectric Layer Modification in Organic Transistor

A series of bithienyl-terminated surfactants with various alkyl chain lengths (from C8 to C13) and phosphono or chlorodimethylsilyl anchoring groups were synthesized by palladium-catalyzed hydrophosphonation, or platinum-catalyzed hydrosilylation as a key step. Surfactants were tested in pentacene or α-sexithiophene-based organic field-effect transistors (OFETs) for the modification of the dielectric surface. The studied surfactants increased the effective mobility of the α-sexithiophene-based device by up to one order of magnitude. The length of alkyl chain showed to be significant for the pentacene-based device, as the effective mobility only increased in the case of dielectric modification with bithienylundecylphosphonic acid. AFM allowed a better understanding of the morphology of semiconductors on bare SiO₂ and surfaces treated with bithienylundecylphosphonic acid.