Effect of Alkyl Groups in Pyrene Chromophore on the Mechanical Response of Pyrene‐Octafluoronaphthalene Co‐Crystals

Changes in the photophysical properties of pyrene ( Py )‐octafluoronaphthalene ( OFN ) co‐crystals ( Py ? OFN ) upon mechanical stimuli are described herein. The Py ? OFN co‐crystal showed a mechano‐induced bathochromic shift in emission, and a similar tendency was observed for the 1,3,6,8‐tetramethylpyrene‐ OFN co‐crystal. These shifts are due to disruption of the microscopic molecular orientation in the co‐crystal, which allows for excimer formation. In sharp contrast to the parent Py ? OFN and methyl‐substituted Py ‐ OFN co‐crystals, no mechano‐induced bathochromic shift was observed when longer alkyl chains were introduced to the 1‐, 3‐, 6‐, and 8‐positions of the Py chromophore. This photophysical opposability against mechanical stimuli could be explained by the orthogonally oriented alkyl groups on the Py ring, which existed between two Py cores like pillars. This fixed OFN to maintain the face‐to‐face alternatively stacked structure of the co‐crystal and thus prevented the formation of the Py excimer. The pillar effect demonstrated herein provides a rational design for co‐crystalline systems that are photophysically stable against mechanical stresses.     

Characterization of Supramolecular Hidden Chirality of Hydrogen‐Bonded Networks by Advanced Graph Set Analysis

Supramolecular hidden chirality of hydrogen‐bonded (HB) networks of primary ammonium carboxylates was exposed by advanced graph set analysis from a symmetric viewpoint in topology. The ring‐type HB (R‐HB) networks are topologically regarded as faces, and therefore exhibit prochirality and positional isomerism due to substituents attached on the faces. To describe the symmetric properties of the faces, additional symbols, Re (right‐handed or clockwise), Si (left‐handed or anticlockwise), and m (mirror), were proposed. According to the symbols, various kinds of faces were classified based on the symmetry. This symmetry consideration of the faces enables us to precisely evaluate supramolecular chirality, especially its handedness, of 0D‐cubic, 1D‐ladder and 2D‐sheet HB networks that are composed of the faces. The 1D‐ladder and 2D‐sheet HB networks generate chirality by accumulating the chiral faces in 1D and 2D manners, respectively, whereas 0D‐cubic HB networks generate chirality based on combinations of eight kinds of faces, similar to the chirality of dice.     

Superstructure-dependent optical and electrical properties of an unusual face-to-face, pi-stacked, one-dimensional assembly of dehydrobenzo[12]annulene in the crystalline state

To develop a novel pi-conjugated molecule-based supramolecular assembly, we designed and synthesized trisdehydrotribenzo[12]annulene ([12]DBA) derivative 2 with three carboxyl groups at the periphery. Recrystallization of 2 from DMSO gave a crystal of the solvate 23 DMSO. Crystallographic analysis revealed, to our surprise, that a face-to-face pi-stacked one-dimensional (1D) assembly of 2 was achieved and that the DMSO molecule played a significant role as a "structure-dominant element" in the crystal. This is the first example of [12]DBA to stack completely orthogonal to the columnar axis. To reveal its superstructure-dependent optical and electrical properties, 2 and its parent molecule 1, which crystallizes in a herringbone fashion, were subjected to fluorescence spectroscopic analysis and charge-carrier mobility measurements in crystalline states. The 1D stacked structure of 2 provides a red-shifted, broadened, weakened fluorescence profile (lambda(max) = 545 nm, phi(F) = 0.01), compared to 1 (lambda(max) = 491 nm, phi(F) = 0.12), due to strong interactions between the p orbitals of the stacked molecules. The charge-carrier mobility of the single crystal of 23 DMSO, as well as 1, was determined by flash photolysis time-resolved microwave conductivity (FP-TRMC) measurements. The single crystal of 23 DMSO revealed significantly-anisotropic charge mobility (sigma(mu) = 1.5x10(-1) cm(2) V(-1) s(-1)) along the columnar axis (crystallographic c axis). This value is 12 times larger than that along the orthogonal axis (the a axis).     

Total synthesis of (-)-martinellic acid via radical addition-cyclization-elimination reaction

The asymmetric total synthesis of martinellic acid, the first pyrrolo[3,2-c]quinoline alkaloid found in nature, is described. Three key steps in our synthesis of (-)-martinellic acid are the Bu(3)SnH-promoted radical addition-cyclization-elimination (RACE) reaction of an oxime ether with an alpha,beta-unsaturated ester to generate the pyrrolo[3,2-c]quinoline core, a chemoselective lactam carbonyl reduction, and guanidinylation under Mitsunobu reaction conditions. The key radical cyclization has also been investigated by using SmI(2). (-)-Martinellic acid was synthesized from commercially available methyl 4-bromo-3-methylbenzoate in fewer steps than previous syntheses and in an improved overall yield.     

A C3‐Symmetric Macrocycle‐Based,Hydrogen‐Bonded,Multiporous Hexagonal Network as a Motif of Porous Molecular Crystals

A C₃‐symmetric π‐conjugated macrocycle combined with an appropriate hydrogen bonding module (phenylene triangle) allowed the construction of crystalline supramolecular frameworks with a cavity volume of up to 58 %. The frameworks were obtained through non‐interpenetrated stacking of a hexagonal sheet possessing three kinds of pores with different sizes and shapes. The activated porous material absorbed CO₂ up to 96 cm³ g^?1 at 195 K under 1 atm.     

Construction of multi-component supramolecular architectures of bile acids and cinchona alkaloids through helical-pitch-synchronized crystallization

Molecular assemblies based on helical motifs are of substantial interest from the view point of fundamental science as well as application. In this study, we propose a new class of organic crystal, that is, heteroH-MOC (multi-component organic crystal containing different kinds of helical motifs consisted of different components), and describe successful construction of heteroH-MOCs with P2(1) and P2(1)2(1)2(1) space groups by using steroidal bile acids and cinchona alkaloids. In the P2(1) crystals, two kinds of helices composed of the steroid and alkaloid are arranged in a parallel fashion, while, in the P2(1)2(1)2(1) crystals, those are in a perpendicular fashion. It is remarkable that, in such systems, particularly in the latter crystals, components ingeniously achieved highly-ordered synchronization of periodicity (helical pitches r and periodic distances in the array of helices p), which is first demonstrated in this study through hierarchical interpretation of the crystal structures.     

Deposition of microcrystalline Ge films using hot-wire technique without toxic gases

To investigate the deposition of Ge films without toxic gas such as germane, we have studied the Ge films prepared by the hot-wire technique, which utilize the reaction between a Ge target and hydrogen atoms generated by the hot-wire decomposition of H₂ gas. The films deposited on Si substrate were microcrystalline Ge films and the mean crystallite size of the films increased from 13.3 to 24.8 nm with increasing the substrate temperature from 300 to 500 °C. Moreover, the deposition rate of Ge films deposited on Si substrate was higher than that of Ge films deposited on Corning 1737 substrate. It was found that the substrate temperature and the kind of substrate are key parameters for the preparation of microcrystalline Ge films by the hot-wire technique.     

Synthesis of α-(aminomethylene)-9-(methoxymethyl)-9H-purine-6-acetic acid derivatives

α-(Aminomethylene)-9-(methoxymethyl)-9H-purine-6-acetamide and the ethyl acetate, 3 and 8 , have been synthesized by catalytic hydrogenation of 6-cyanomethylene-9-methoxymethylpurine derivatives 2 and 7 which were obtained by the substitution of 6-chloro-9-(methoxymethyl)purine ( 1 ) with α-cyanoacetamide and ethyl cyanoacetate, respectively. Substitution of 3 and 8 with amines gave the corresponding N-substituted α-(aminomethylene)-9-(methoxymethyl)-9H-purine-6-acetamide and the ethyl acetate 4 and 10 . Reaction of 3 with piperidine gave 9-(methoxymethyl)-9H-purine-6-acetamide ( 5 ).     

Synthesis of 3-(β-D-ribofuranosyl)pyrazolo[3,2-i]-purine derivatives and their cytotoxic activities

9-Amino-3-(β-D-ribofuranosyl)pyrazolo[3,2-i|purine ( 6 ) has been prepared from a fully protected 3-(β-D-ribofuranosyl)pyrazolo[3,2-i]purine ( 2 ) and the 9-bromo substituted derivative 3 by nitration, followed by reduction. Reaction of 9-bromo-3-(β-D-ribofuranosyl)pyrazolo[3,2-i)purine ( 1b ) with alkali gave the (pyrazol-3-yl)imidazole derivative, followed by diazocyclization with sodium nitrate to give 9-bromo-3-(β-D-ribofuran-osyl)imidazolo[4,5-d]pyrazolo[2,3-c][1,2,3]triazine ( 10 ) after deacetylation. Compounds 6 and 10 exhibited cytotoxic activity against leukemia cells.