Intensely Fluorescent Azobenzenes: Synthesis,Crystal Structures,Effects of Substituents,and Application to Fluorescent Vital Stain

2‐[Bis(pentafluorophenyl)boryl]azobenzenes bearing hydrogen, methoxy, dimethylamino, trifluoromethyl, fluoro, n‐butyl, and tert‐butyldimethylsiloxy groups at the 4′‐position or methoxy and bromo groups at the 4‐position have been synthesized. The 4‐bromo group of the 2‐boryl‐4‐bromoazobenzene derivative was converted to phenyl and diphenylamino groups by palladium‐catalyzed reactions. The absorption and fluorescence properties have been investigated using UV/Vis and fluorescence spectroscopy. The 2‐borylazobenzenes emitted an intense green, yellow, and orange fluorescence, in marked contrast to the usual azobenzene fluorescence. The 4′‐siloxy derivative showed the highest fluorescence quantum yield (0.90) among those reported for azobenzenes to date. The correlation between the substituent and the fluorescence properties was elucidated by studying the effect of the substituent on the relaxation process and from DFT and TD‐DFT calculations. An electron‐donating group at the 4′‐position was found to be important for an intense emission. Application of fluorescent azobenzenes as a fluorescent vital stain for the visualization of living tissues was also investigated by microinjection into Xenopus embryos, suggesting these compounds are nontoxic towards embryos.     

Chain‐growth condensation polymerization of 4‐aminobenzoic acid esters bearing tri(ethylene glycol) side chain with lithium amide base

Chain‐growth condensation polymerization of p‐aminobenzoic acid esters 1 bearing a tri(ethylene glycol) monomethyl ether side chain on the nitrogen atom was investigated by using lithium 1,1,1,3,3,3‐hexamethyldisilazide (LiHMDS) as a base. The methyl ester monomer 1a afforded polymer with low molecular weight and a broad molecular weight distribution, whereas the polymerization of the phenyl ester monomer 1b at ?20 °C yielded polymer with controlled molecular weight (M_n = 2800–13,400) and low polydispersity (M_w/M_n = 1.10–1.15). Block copolymerization of 1b and 4‐(octylamino)benzoic acid methyl ester ( 2 ) was further investigated. We found that block copolymer of poly 1b and poly 2 with defined molecular weight and low polydispersity was obtained when the polymerization of 1b was initiated with equimolar LiHMDS at ?20 °C and continued at ?50 °C, followed by addition of 2 and equimolar LiHMDS at ?10 °C. Spherical aggregates were formed when a solution of poly 1b in THF was dropped on a glass plate and dried at room temperature, although the block copolymer of poly 1b and poly 2 did not afford similar aggregates under the same conditions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1357–1363, 2010     

Direct Near Infrared Light–Activatable Phthalocyanine Catalysts

The high penetration of near-infrared (NIR) light makes it effective for use in selective reactions under light-shielded conditions, such as in sealed reactors and deep tissues. Herein, we report the development of phthalocyanine catalysts directly activated by NIR light to transform small organic molecules. The desired photocatalytic properties were achieved in the phthalocyanines by introducing the appropriate peripheral substituents and central metal. These phthalocyanine photocatalysts promote cross-dehydrogenative-coupling (CDC) under irradiation with 810 nm NIR light. The choice of solvent is important, and a mixture of a reaction-accelerating (pyridine) and -decelerating (methanol) solvents was particularly effective. Moreover, we demonstrate photoreactions under visible-light-shielded conditions through the transmission of NIR light. A combined experimental and computational mechanistic analysis revealed that this NIR reaction does not involve a photoredox-type mechanism with electron transfer, but instead a singlet-oxygen-mediated mechanism with energy transfer.     

Organic phosphorus compounds. IV. Asymmetric 4-(benzothiazol-2-yl)benzylphosphonates as potent calcium antagonistic vasodilators

Various asymmetric or cyclic ester derivatives of the phosphonic acid moiety in the calcium antagonist fostedil (KB-944) were synthesized. The coronary vasodilator activity of these compounds was assessed by Langendorff's method. Among them, the ethyl isopropyl ester 12 showed the most potent activity, which was comparable to that of fostedil.     

13C- and 1H-NMR and FTIR spectroscopic evidence for aggregate formation of organosilanes in toluene

 Changes in the ¹³C and ¹H NMR chemical shifts of the silane coupling agent (3-aminopropyltri-ethoxysilane, APTS) in toluene, which were detected as the concentration of APTS increased, have been interpreted in terms of the formation of micelles and the presence of a critical micelle concentration (CMC) equal to ca. 0.47 mol 1^-1. For the protons of the n-propyl segment, ¹H NMR splitting patterns have been analyzed and conformations of the propyl segment have been discussed. Plots of relative absorbance of the two NH₂ stretch IR bands at 3324 and 3384 cm^-1 against concentration provided an inflection point (corresponding to the CMC) at a value equal to 0.46 mol 1^-1. Thus, consideration of the interaction of APTS with a surface must take into account the presence of both APTS aggregates as well as APTS monomers. Received: 16 August 1996 Accepted: 26 September 1996     

A facile synthesis of [3ncyclophanes,in which aromatic rings are connected with -CH2CO-CH2- bridges

The title compounds, I, were synthesized by the dialkylation of TosMIC, II, with appropriate bis (halomethyl) compounds, III, under phase-transfer condition, followed by acid hydrolysis.     

Backbone rearrangements of methyl (-)-kaur-9(11)-en-19-oate and its epoxide: structures of two diterpenes of a new skeletal type

cleavage of the epoxide ($\text{2}$) of methyl (-)-kaur-9(11)-en-19-oate ($\text{1b}$) with boron trifluoride-ether in benzene and in acetic anhydride yielded ($\text{3a}$) and ($\text{3b}$), respectively. On epoxidation with $\text{m}$-chloroperbenzoic acid in the presence of $\text{N}$-nitrosomethyl urea, ($\text{1b}$) suffered a backbone rearrangement to form ($\text{6}$).