Control over molecular motion using the cis–trans photoisomerization of the azo group

• Estíbaliz Merino and
• María Ribagorda

Beilstein J. Org. Chem. 2012, 8, 1071–1090, doi:10.3762/bjoc.8.119

• .8.119 Abstract Control over molecular motion represents an important objective in modern chemistry. Aromatic azobenzenes are excellent candidates as molecular switches since they can exist in two forms, namely the cis (Z) and trans (E) isomers, which can interconvert both photochemically and thermally

• external stimuli. Keywords: azobenzenes; molecular switches; nanomachines; photoisomerization; Review This review is based on an article published in 2009 in Anales de Química (Real Sociedad Española de Química) [1]. Azobenzene was described for the first time in 1834 [2] and one century later, in 1937

• switches described so far. The azobenzenes are organic molecules that present two aromatic rings linked by an azo group (N=N). They have properties that have led to some applications of great importance, mainly for the chemical industry. The azobenzenes are highly coloured compounds and belong to the group

The effect of the formyl group position upon asymmetric isomeric diarylethenes bearing a naphthalene moiety

• Renjie Wang,
• Shouzhi Pu,
• Gang Liu and
• Shiqiang Cui

Beilstein J. Org. Chem. 2012, 8, 1018–1026, doi:10.3762/bjoc.8.114

• molecules must possess the following properties: (1) low cytotoxicity, (2) high sensitivity, (3) easy chemical modification. In the past few decades, various types of photochromic molecules, such as fulgides, spiropyranes, azobenzenes, and diarylethenes, have been developed [2][23][24][25][26][27][28][29

Recent advances towards azobenzene-based light-driven real-time information-transmitting materials

• Jaume García-Amorós and
• Dolores Velasco

Beilstein J. Org. Chem. 2012, 8, 1003–1017, doi:10.3762/bjoc.8.113

• devices. Many different organic photochromic molecules are known in photochemistry, such as azobenzenes, stilbenes, spiropyranes, fulgides, diarylethenes and chromenes among many others (Figure 1) [16]. The photochromic processes that take place when such compounds are illuminated can be divided in three

• to the initial isomer even at elevated temperatures (e.g., fulgides and diarylethenes). ● T-type (thermally reversible type); the photogenerated isomer thermally reverts to the initial form (e.g., azobenzenes, stilbenes or spiropyranes). One of the most used organic chromophores for optical switching

• applications are certainly azobenzenes. Azobenzene, a photochromic T-type system, exhibits a reversible isomerisation process between its trans and cis isomers of different stability. In this process, the photoreaction simply causes the rearrangement of the electronic and nuclear structure of the molecule

Diarylethene-modified nucleotides for switching optical properties in DNA

• Sebastian Barrois and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2012, 8, 905–914, doi:10.3762/bjoc.8.103

• [5][6][7][8], azobenzenes [9], spirobenzopyrans [10] and diarylethenes [11] represent the most promising candidates for introducing photoswitching functionality into biopolymers, and thereby for regulating biological activity [12][13]. Azobenzenes were designed and synthesized as artificial

• polymerase reaction [18], photocontrol DNA triplex formation [19], and drive photon-fueled DNA-based nanomachines [20][21]. Concerning the extent of structural change, the cis–trans isomerization of azobenzenes behaves much simpler than the ring opening of spiropyrans to merocyanines. In the latter case not

Building photoswitchable 3,4'-AMPB peptides: Probing chemical ligation methods with reducible azobenzene thioesters

• Gehad Zeyat and
• Karola Rück-Braun

Beilstein J. Org. Chem. 2012, 8, 890–896, doi:10.3762/bjoc.8.101

• 4,5,6-trimethoxy-2-mercaptobenzyl auxiliary as well as the Nα-2-mercaptoethyl auxiliary. Thus, 3,4'-AMPB derivatives/peptides proved to be significantly less prone to reduction by aliphatic and aromatic thiols than were the 4,4'-AMPB compounds. Keywords: acyl transfer auxiliary; azobenzenes; ligation

• ; molecular switches; peptides; redox chemistry; Introduction Optical switches not only offer the advantage to elucidate, but also to control biological processes with high spatial and temporal resolution by using light, either in vitro or in vivo [1]. In this context, azobenzenes remain a privileged class

• thiol molecule at the N-sulfenohydrazodiarene B, yielding the symmetric disulfide and the respective hydrazine thioester or hydrazine peptide (Scheme 3, reaction 2). The reduction of diazene units by thiols has been intensively studied in the past for electron-poor azobenzenes or azodicarboxylates, en

meta-Oligoazobiphenyls – synthesis via site-selective Mills reaction and photochemical properties

• Raphael Reuter and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2012, 8, 877–883, doi:10.3762/bjoc.8.99

• -azobenzenes did not show any photochromicity. Therefore, in recent examples in the literature the azo-units have been dissected by incorporation of biphenyl units. Hecht and co-workers investigated the effect of the electronic coupling in detail and showed that the incorporation of ortho-methyl groups on the

• . Isomerization studies Compounds 13, 15, 16 and 2 were analyzed by UV spectroscopy. All of them exhibit the typical behavior of azobenzenes, with a strong absorption at 330 nm for the π–π* transition and a weak absorption at 430 nm for the n–π* transition (Figure 3). For compounds 16 and 2 an increased

Molecular switches and cages

• Dirk Trauner

Beilstein J. Org. Chem. 2012, 8, 870–871, doi:10.3762/bjoc.8.97

• photoswitches continue to emerge and “old friends”, such as azobenzenes are constantly improved and optimized. This is not only true with respect to their photophysical properties but also with regard to their synthetic accessibility. Indeed, as molecular switches are applied in ever-increasing quantities, the

• features include their absorption spectra, conductivity, geometry and bistability, as well as their polarity, solubility, efficacy, or catalytic activity. Photoswitches are covered extensively, ranging from diarylethenes (Pu, Wagenknecht) to dihydroazulenes/vinylheptafulvenes (Nielsen) and azobenzenes

• (Rück-Braun, Hoppmann). Two reviews discuss cis-azobenzenes with rapid thermal isomerization kinetics (Velasco), and highlight the azobenzene moiety as one of the smallest light-driven molecular motors conceivable (Merino). Issues of bistability are also addressed in an account on shape-persistent

Azobenzene dye-coupled quadruply hydrogen-bonding modules as colorimetric indicators for supramolecular interactions

• Yagang Zhang and
• Steven C. Zimmerman

Beilstein J. Org. Chem. 2012, 8, 486–495, doi:10.3762/bjoc.8.55

• and exhibit a range of vivid colors. Furthermore, the application of azobenzenes in chemistry is quite broad and includes their use as switches [42], in nonlinear optics [43], sensing devices [44], and in nanostructured films for optical storage [45]. Although this work does not focus on switching

Synthesis of novel photochromic pyrans via palladium- mediated reactions

• Christoph Böttcher,
• Gehad Zeyat,
• Saleh A. Ahmed,
• Elisabeth Irran,
• Thorben Cordes,
• Cord Elsner,
• Wolfgang Zinth and
• Karola Rueck-Braun

Beilstein J. Org. Chem. 2009, 5, No. 25, doi:10.3762/bjoc.5.25

• -electronic devices, e.g. as logic gates [1]. In the life sciences, functionalized azobenzenes [6], hemithioindigos [7][8] and fulgimides [9][10] among other classes of photoswitches, have already proven to be valuable tools for photo-controlling the structure and function of complex biomolecules [6][7][8][9