Multi‐Pyrene Assemblies Supported on Stannoxane Frameworks: Synthesis,Structure and Photophysical Studies

Organostannoxanes have been used as scaffolds for the preparation of multi‐chromophore assemblies. A single‐step synthesis procedure allows the preparation of compounds in which the number of chromophore units can be varied from two to six. Thus, the reactions of pyrene sulfonic acid (PySO₃H) or C₁₆H₉CHNC₆H₃(COOH)₂ (LH₂) with various organotin precursors gave pyrene‐containing organostannoxanes, that is, [Ph₃SnPySO₃]₆ ( 1 ), [{(Me₂Sn)₂(μ₃‐O)(μ‐OH)PySO₃}₂{(Me₂Sn)₂(μ₃‐O)(μ‐OH)H₂O}₂ ? 2 PySO₃] ( 2 ), [{tBu₂Sn(OH)PySO₃}₂] ( 3 ), [{(nBuSn)₁₂(O)₁₄(OH)₆{PySO₃}₂] ( 4 ), and [{(nBu₂Sn)L}₃]₂ ? C₆H₅CH₃ ( 5 ). Compounds 1 – 5 were characterized by using X‐ray crystallography. Compounds 1 and 5 are 24‐membered macrocycles. Macrocycle 1 possesses intramolecular π–π stacking interactions. An unusual co‐crystal of two tetrameric ladders in 2 was observed in which one of the components of the co‐crystal is neutral whereas the other is dicationic and two pyrenesulfonate counterions are present to balance the overall charge. In the solid state these compounds reveal rich supramolecular structures. Photophysical studies on 1 – 5 reveal that interactions in the solid state lead to considerable broadening of the emission bands.     

Conformational dependence of tag induced intramolecular STM contrast in hexaphenylbenzene molecules

Chemically tagged hexaphenylbenzene molecules physisorbed on Au(1 1 1) surface display their tag differently under STM as compared to their physisorption on a Cu(1 1 1) surface. Our STM findings complemented by First Principles and Quantum Chemistry calculations have attributed this difference to two different conformations adopted by these molecules on Au(1 1 1) in comparison to its one conformation on Cu(1 1 1). The demonstration of the sensitivity of the tag to its electronic or chemical environment would have important implications in designing single molecule machinery where the motion of the molecule is to be discerned by tracking its tag induced intramolecular STM contrast.     

Liquid Crystals of Disc-like Molecules

The paper deals with thermotropic mesomorphism in pure compounds composed of disc-like molecules. The disc-like mesogens known to date are reviewed and the present state of knowledge of the structures of the mesophases are described. A few brief remarks are made about the physics of these new systems.     

Some Comments on the Determination of Enthalpies of Liquid Crystalline Transitions by Differential Scanning Calorimetry

We demonstrate a simple practical method of improving the accuracy of determination of enthalpies of liquid crystalline transitions by differential scanning calorimetry. The method involves measurements at different heating rates and interpolation to zero heating rate.     

Single crystal EPR and optical studies of paramagnetic ions doped zinc potassium phosphate hexahydrate—Part II: VO(II)—a case of substitutional site

Single crystal electron paramagnetic resonance (EPR) studies were carried at room temperature for VO(II) doped zinc potassium phosphate hexahydrate. The results indicate that the paramagnetic impurity has entered the lattice only substitutionally, as confirmed by the single crystal rotations. The spin Hamiltonian parameters calculated from the spectra are g_//=1.9356, g=1.9764, A_//=200.9 G and A=76.5 G. The optical absorption spectrum exhibits three bands (800, 670 and 340 nm) suggesting the C_4v symmetry and the optical parameters evaluated are Dq=1492, Ds=−3854 and Dt=186 cm⁻¹.