Mesomorphic Behavior of Symmetric Azomethine Dimers Containing Different Chromophore Groups

Pyrene-Fused Poly-Aromatic Regioisomers: Synthesis, Columnar Mesomorphism, and Optical Properties

π-Extended pyrene compounds possess remarkable luminescent and semiconducting properties and are being intensively investigated as electroluminescent materials for potential uses in organic light-emitting diodes, transistors, and solar cells. Here, the synthesis of two sets of pyrene-containing π-conjugated polyaromatic regioisomers, namely 2,3,10,11,14,15,20,21-octaalkyloxypentabenzo[a,c,m,o,rst]pentaphene (BBPn) and 2,3,6,7,13,14,17,18-octaalkyloxydibenzo[j,tuv]phenanthro [9,10-b]picene (DBPn), is reported. They were obtained using the Suzuki-Miyaura cross-coupling in tandem with Scholl oxidative cyclodehydrogenation reactions from the easily accessible precursors 1,8- and 1,6-dibromopyrene, respectively. Both sets of compounds, equipped with eight peripheral aliphatic chains, self-assemble into a single hexagonal columnar mesophase, with one short-chain BBPn homolog also exhibiting another columnar mesophase at a lower temperature, with a rectangular symmetry; BBPn isomers also possess wider mesophase ranges and higher mesophases' stability than their DBPn homologs. These polycyclic aromatic hydrocarbons all show a strong tendency of face-on orientation on the substrate and could be controlled to edge-on alignment through mechanical shearing of interest for their implementation in photoelectronic devices. In addition, both series BBPn and DBPn display green-yellow luminescence, with high fluorescence quantum yields, around 30%. In particular, BBPn exhibit a blue shift phenomenon in both absorption and emission with respect to their DBPn isomers. DFT results were in good agreement with the optical properties and with the stability ranges of the mesophases by confirming the higher divergence from the flatness of DBPn compared with BBPn. Based on these interesting properties, these isomers could be potentially applied not only in the field of fluorescent dyes but also in the field of organic photoelectric semiconductor materials as electron transport materials.

UV light sensing and switching applications of dimeric smectic liquid crystals: comparative calculations

Two dimeric smectic molecules, namely α-ω-bis (4-n-pentylanilinebenzylidene-4'-oxy) butane (PABO4) and α-ω-bis (4-n-pentylanilinebenzylidene-4'-oxy) pentane (PABO5), have been considered for sensing UV light. The compounds' optimization process has been performed through B3LYP hybrid functional together with basis set 6-31+G (d) using the input parameters from the crystallographer. The absorption of UV analysis of these compounds has been estimated, and the configuration interaction single-level method has been used to analyse the electronic transition features coupled with the calculation of excited states using semi-empirical Hamiltonian ZINDO. The CNDO/S, INDO/S together with CI approaches, has been utilized for comparative evaluation. The spectral-associated parameters have been summarized. The molecules discussed in this manuscript present several features, viz. the absorption range of the molecules that is sensitive to different wavelengths, the usage in flexible devices, offering the prospect for UV sensors. Further, the switching applications have been explored based on the oscillator strength data in various regions of wavelengths.