This paper described a series of trimeric halogen bonded supramolecular thermotropic liquid crystals. The halogen bonding interaction was studied by infrared and X-ray photoelectron spectroscopy. It was observed that the aromatic skeleton infrared vibration of halogen bonded acceptor molecules had moved to higher frequencies relative to their corresponding unbonded counterparts. The halogen-bonded acceptors showed higher N 1s binding energies of 0.89-1.12 eV than those of unbonded components. In contrast, the halogen-bonded donors displayed lower I 3d binding energies than their corresponding unbonded species. The changes in binding energies and in infrared frequencies demonstrated the presence of effective halogen bonding interaction. The thermal behaviors of the halogen-bonded complexes were examined using differential scanning calorimetry and optical polarizing microscopy. Most of the trimeric complexes exhibited thermotropic liquid crystals with smectic A phases. The effect of length in spacers and terminal groups in halogen bond molecules on mesophase transition temperatures was investigated, revealing that there was little correlation between the length in spacers and terminal groups and phase transition temperatures.

Two model compounds, 1,3-bis(9,9-dihexylfluoren-2-yl)azulene (M1), and 1,3-bis[7-(9,9,9′,9′-tetrahexyl-2,2′-bifluoren-7-yl)azulene (M2), and polymers, poly[2,7-(9,9-dialkylfluorenyl)-alt-(1′,3′-azulenyl)] (P1−P4) and poly{[1,3-bis(9′,9′-dihexylfluoren-2′-yl)azulenyl]-alt-[2′′,7′′-(9′′,9′′-dialkylfluorenyl]} (P5, P6) were synthesized by reacting 1,3-dibromoazulene or 1,3-bis(7-bromo-9,9-dihexylfluoren-2-yl)azulene with a suitable 9,9-dialkylflourenyl-2-borate or 2,7-diborate via Suzuki cross-coupling reactions. The thermal and optical properties of the polymers were characterized by thermogravimetric analysis, differential scanning calorimetry, and UV−vis and fluorescence spectroscopy. M1, M2, and P1−P6 are nonfluorescent in the neutral state in different organic solvents. However, M1, M2, P5, and P6 become fluorescent upon the addition of trifluoroacetic acid in THF, with relative quantum efficiencies of 0.004−0.06. The “switching on” of the fluorescence for the azulene−fluorene copolymers and model compounds is due to the formation of a 6π electron aromatic azulenium cation, which alters the overall electronic character, particularly, the HOMO and LUMO, and subsequently the band gap. Cyclic voltammograms of polymer films prepared by spin-coating polymer solution onto an indium−tin oxide-coated glass substrate showed that all of the polymers films exhibited the relatively low half-wave oxidation potentials in the range 0.84−0.93 V vs Ag/AgCl. Electrochromic devices of P3 and P5 with a sandwich structure of PET-ITO/polymer/PMMA-PC-LiClO4/PET-ITO were fabricated, and color changes from light yellow to brown and from yellow to green for polymers P3 and P5 films, respectively, are observed.

Two highly air-sensitive asymmetric ligands (+/-)-diphenyl[1-(1-naphthyl)ethyl]phosphine and its arsenic analogue [(+/-)-L] have been prepared and resolved by the fractionalization of a pair of diastereomeric palladium complexes containing the appropriate ligand and ortho-metalated (R)-(1-(dimethylamino)ethyl)naphthylene. X-ray structural analysis revealed that the less soluble isomers in each resolution contained the resolving ligand of the S absolute configuration. The resolved ligands coordinated as monodentates with only the phosphorus or arsenic donor coordinated to the resolving organopalladium unit. Due to the steric congestions between the phenyl and the naphthyl rings, the Ph(2)E-C distances in both monodentate ligands are unusually long [1.885(2) A for E = P and 2.035(7) A for E = As]. The (R)-naphthylamine auxiliary could be removed chemoselectively from the resolved complexes by treatment with concentrated hydrochloric acid to give the corresponding bis(micro-chloro) complexes (-)-[(S)-LPdCl(2)](2). Treatments of these dimeric complexes with sodium acetate in ethanol gave the novel ortho-metalated complex bis(micro-chloro)bis[(S)-1-[1-(diphenylphospha)ethyl]naphthylenyl-C(2),P]dipalladium(II), with [alpha](D) +559 degrees (CH(2)Cl(2)), and the analogous ortho-metalated (S)-arsa complex, with [alpha](D) +349 degrees (CH(2)Cl(2)). The Ph(2)E-C distances recorded for the ortho-metalated phosphine complex are 1.841(6) and 1.846(5) A, and those recorded for the organometallic arsa rings are 1.938(9) and 1.945(9) A. These Ph(2)E-C distances are noticeably shorter than those recorded for their analogous monodentate complexes. The intrachelate E-Pd-C angles of the analogous amino, phospha, and arsa complexes involved in the current study are similar [within the range of 80.5(2)-82.1(3) degrees ] although it is noticeable that As > P > N.

The ortho palladation of prochiral (di-tert-butyl)(diphenylmethyl)phosphine proceeded readily to give rise to the dimeric complex, di-mu-chlorobis{[(phenyl)(di-tert-butylphosphino)methyl]phenyl-C2, P}dipalladium(II). The (S,S)-(+)-dimer was subsequently obtained by optical resolution with sodium (S)-prolinate. The absolute configuration of the optically resolved (+)-dimer was concluded from the X-ray diffraction studies of the derivatized O,O-acetylacetonate complex. The availability of the (+)-dimer is crucial to the study of the properties of the Pd-C bond. The phosphapalladacycle Pd-C bond exhibited a remarkable thermodynamic stability. It could not be permanently ruptured to give rise to the eta1-P monodentate even in a refluxing acetone solution containing concentrated hydrochloric acid. Instead, the phosphine was noted to fluctuate between the ring closed and opened states via the reversible Pd-C bond cleavage/formation under this condition. Inevitably, this resulted in the racemization of the five-membered organopalladium ring structure. In contrast, such bond cleavage was not observed at room temperature in the absence of HCl. In fact, the phosphine was observed to readily ortho palladate even under conditions not favorable to cyclopalladation. Indeed, the difficulty of isolating the phosphine as a simple eta1-P monodentate coordination complex was further noted by its lack of reactivity toward the N,N-dimethyl-1-(1'naphthyl)ethylaminate palladacycle mu-chloro dimer. Only by enhancing the Lewis acidity of the palladacycle in the form of the positively charged bis(acetonitrile) complex could the phosphine be encouraged to participate in monodentate eta1-P bonding. Even then, this form of coordination was weak and was only observed by NMR spectroscopy.