Shape‐Switchable Azo‐Macrocycles

Abstract

The synthesis of four shape‐switchable macrocycles comprising different peripheral substituents is described. The macrocycles 1–4 consist of m‐terphenyl semicircles interlinked by two azo joints. These macrocycles were assembled from nitro‐functionalized m‐terphenyl moieties through reductive dimerization. The semicircles were assembled through Suzuki cross‐coupling reactions. The molecular weights of the macrocycles were determined by vapour pressure osmometry, because mass spectrometry failed in the cases of 2 and 3. The E → Z photoisomerization reactions were analysed by UV/Vis spectroscopy complemented by 1H NMR studies. A very slow thermal back‐reaction indicated considerable stabilization of the Z isomer. The reduced efficiency of the thermal back‐reaction probably arises from the reduced degree of freedom due to the mechanical interlinking of the two azo groups. The photostationary state consisted of all‐Z (85 %) and all‐E isomers (15 %). The E → Z transformation induced by irradiation displayed simple exponential kinetics, which indicates pairwise switching of the two azo groups in a macrocycle, at least on the timescale under investigation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

A Chiral Macrocyclic Oligothiophene with Broken Conjugation – Rapid Racemization through Internal Rotation

“…[34] Therefore, a procedure utilizing Kumada reaction conditions as developed by Rozenberg et al was adapted. [49] Commercially available 2-thienyl magnesium bromide (13) was added dropwise to a suspension of pseudo-para-dibromo-PC (14) and Pd-(dppf)Cl 2 in tetrahydrofuran (THF). After heating to 60°C for two h, building block 6 started to precipitate from the mixture.…”

“…[8] [9] Various molecular motifs have been reported as subunits of conjugated macrocyclic compounds, like e. g. pyridines, benzenes, acetylenes, as well as fivemembered aromatic heterocycles, like furans and thiophenes. [10] [11] We reported the assembly and investigation of a variety of macrocycles consisting of aromatic subunits in the past, among others structures comprising functional subunits like redox chromophores [12] [13] or optically addressable azo-benzenes, [14] macrocycles designed as single molecule switches [15 -17] or with pronounced π-stacking features, [18] [19] and giant macrocycles as model compounds for persistent ring currents. [20] More recently, our focus moved to axial chiral systems like bicyclic 'Geländer'-type structures [21] or the macrocyclization of the ligands assembled in a M(II) terpyridine complex resulting in a helical macrocycle with an arrangement resembling a propeller.…”

Enhancement of the photochromic switching speed of bithiophene azo dyes

“…[17][18][19][20][21][22][23][24] The performance of these materials rely on our ability to control the kinetics of the E-Z photoisomerization which can be achieved by the proper choice of the environmental media 3,6 or by the change in the azobenzene structure. [25][26][27][28] Although a large variety of diarylazo compounds are used in the design of optical materials, only a few reports concerning the photoisomerization of heterocyclic azo dyes can be found in the literature. [29][30] In the last years we have synthesized a large variety of heterocyclic azo dyes substituted by electron-donating and electron-withdrawing groups ('push/pull' substitution pattern) that possess solvatochromic, photochromic and nonlinear optical (NLO) properties which are influenced by the electronic nature of the -conjugated bridge (thienylpyrrole or bithiophene) and by the substitution pattern on the aryl and heteroaryl-diazene moieties (Figure 1).…”

Controlling charge-transfer properties through a microwave-assisted mono- or bis-annulation of dialkynyl-N-(het)arylpyrroles

“…, 2b and 2d were prepared according to previously reported procedure. 24 Pyrroles 3a, 13 3b 15 and 3d 18 have been described previously. Sonogashira coupling procedures were adapted from literature.…”