The nucleation and growth mechanism and polymorph-property correlations in the molecular cocrystal field are widely sought but currently remain unclear. Herein, a new wire-like morphology of phenazine(Phz)-chloranilic acid(H2ca) cocrystal(PHC) is demonstrated for the first time, and the self-assembly of Phz and H2ca is controlled to selectively prepare kinetically stable wires and thermodynamically stable plates. Specifically, low precursor concentration is beneficial for one-dimensional(1D) self-assembly along the [010] crystallographic direction, while only supersaturation can trigger 2D self-assembly along the [100] and [010] directions, respectively. This is understandable in terms of the(020) face showing the largest attachment energy(Eatt) and the(002) face possessing the smallest surface energy(Esurf). Moreover, anisotropic Raman spectra related to the mode symmetry and atomic displacements in two types of PHCs are revealed, and the same Raman-active vibrational bands of PHC wire and plate show different polarization responses, which is intrinsically ascribed to their different molecular orientations.Overall, this is the first case that morphologies of cocrystal are precisely tuned with comprehensive investigations of their anisotropic vibrational characteristics.
Weigang ZhuYunli WangChengcheng HuangLingyun ZhuYonggang ZhenHuanli DongZhixiang WeiDong GuoWenping Hu
Compact molecular packing with short π-π stacking and large π-overlap in organic semiconductors is desirable for efficient charge transport and high carrier mobility. Thus charge transport anisotropy along different directions is commonly observed in organic semiconductors. Interestingly, in this article, we found that comparable charge transport property were achieved based on the single crystals of a bis-fused tetrathiafulvalene derivative （EM-TTP） compound along two interaction directions, that is, the multiple strong S…S intermolecular interactions and the π-π stacking direction, with the measured electrical conductivity and hole mobility of 0.4 S cm-1, 0.94 cm2 V i s 1 and 0.2 S cm-1, 0.65 cm2 V-1 s-1, respectively. This finding provides us a new molecular design concept for developing novel organic semiconductors with isotropic charge transport property through the synergistic effect of multiple intermolecular interactions （such as π-π interactions） and π-π stacking.
Two dysprosium(Ⅲ) complexes derived from 2,2'-bipyridine-6,6'-dicarboxylic acid(H_2bpdc),[Dy(bpdc)(Hbpdc)]-3H_2O(1) and[Dy_2(bpdc)_3(H_2O)_3]·2.125H_2O(2),were isolated from the same hydrothermal reaction container as different phases.Compound1 is a mononuclear complex with a DyN_4O_4 coordination polyhedron;whereas compound 2 is a dinuclear complex with two types of eight coordinated dy sprosium(Ⅲ) ions,showing DyN_4O_4 and DyN_2O_6 coordination polyhedra,respectively.Remarkably,a new type of(H_2O)_6 supramolecular aggregate exists in the crystal structure of 2.Magnetic investigations revealed that 1 is a field-induced single-ion magnet with an effective energy barrier of 45.6 K,exhibiting two-step magnetic relaxation;while an intramolecular ferromagnetic interaction exists in 2,which is a field-induced single-molecule magnet,displaying two-step magnetic relaxation too,with effective energy barriers of 53.4 and 92.1 K,respectively.
It is a common phenomenon for organic semi- conductors to crystallize in two or more polymorphs, leading to various molecular packings and different charge transport properties. Therefore, it is a crucial issue of tuning molec- ular crystal polymorphs （i.e., adjusting the same molecule with different packing arrangements in solid state） towards efficient charge transport and high performance devices. Here, the choice of solvent had a marked effect on con- trolling the growth of a-phase ribbon and β-phase platelet during crystallization for an indenofluorene （IF） π-extended tetrathiafulvalene （TTF）-based cruciform molecule, named as IF-TTF. The charge carrier mobility of the a-phase IF-TTF crystals was more than one order of magnitude higher than that of β-phase crystals, suggesting the importance of reasonably tuning molecular packing in solid state for the improvement of charge transport in organic semiconductors.
