1+1≥2? Norbornadiene‐Azobenzene Molecules as Multistate Photoswitches

Abstract

By combination of two photochromic molecules as multistate photoswitches new properties regarding to molecular solar thermal (MOST) energy storage systems and information storage capacity of smart materials are expected. By fusing the azobenzene with the norbornadiene system, new multinary photoswitches were designed. A successful synthesis towards different analogues was developed via Suzuki coupling reaction as key step. The isomerization behaviour of these norbornadiene‐azobenzene fusions was studied by UV‐Vis and 1H NMR spectroscopy in different solvents investigating the electronic communication within these multinary‐photochromic systems.

Borylated norbornadiene derivatives: Synthesis and application in Pd-catalyzed Suzuki–Miyaura coupling reactions

“…Thus, the coupling reaction of 2a with 1-bromonaphthalene ( 4b ), 2-bromotoluene ( 4c ), 3-bromoanisole ( 4e ), 2-bromoanisole ( 4f ) 2-bromonitrobenzene ( 4h ), 3-iodo-4-methoxybenzonitrile ( 4i ), and 2-bromopyridine ( 4j ) gave the corresponding 2-arylnorbornadienes in moderate to good yields (32–67%), whereas the reaction with the 4-cyano- and 4-methoxy-substituted halobenzene derivatives 4d and 4g gave the corresponding products only in low yield or not at all ( Scheme 2 ). It should be noted, however, that the relatively low yields of some coupling reactions are also caused by the difficult purification of the products, because most of them tend to decompose slowly in solution or during chromatographic work-up [ 31 , 34 ]. The novel compounds 5b – j were identified and fully characterized by NMR spectroscopy ( 1 H, 13 C, COSY, HSQC, HMBC); however, correct elemental analysis was not obtained in the case of the less-stable products 5d , 5g and 5j .…”

“…In another versatile approach, arylation and alkenylation reactions of the norbornadiene may be accomplished with a Suzuki–Miyaura coupling reaction. In this case, halogenated norbornadienes react with arylboronic acids or their esters to the corresponding aryl-substituted norbornadienes under optimized conditions [ 28 – 31 ]. To the best of our knowledge, however, no borylated norbornadiene derivatives have been employed in Suzuki–Miyaura coupling reactions so far, although this synthetic route appears to be a useful complementary approach to the already established one.…”

Arylazo-1,2,3-Triazoles: “Clicked” Photoswitches for Versatile Functionalization and Electronic Decoupling

“…It is well-documented that the photoreactivity can be dramatically decreased if a photoswitch is electronically coupled to another π-conjugated unit. [43][44][45][46][47][48][49] To address this issue, the effect of linker structure on the strength of electronic coupling has been widely investigated, and several decoupling strategies for azobenzenes have been developed, as illustrated in Figure 1a. Complete decoupling can be simply achieved by inserting a sp 3 -CH group as the spacer, e.g., a methylene or an aliphatic chain, which is nonetheless not suitable for designing rigid molecular architectures.…”

Arylazo-1,2,3-Triazoles: “Clicked” Photoswitches for Versatile Functionalization and Electronic Decoupling

“…It is well-documented that the photoreactivity can be dramatically decreased if a photoswitch is electronically coupled to another π-conjugated unit. [43][44][45][46][47][48][49] To address this issue, the effect of linker structure on the strength of electronic coupling has been widely investigated, and several decoupling strategies for azobenzenes have been developed, as illustrated in Figure 1a. Complete decoupling can be simply achieved by inserting a sp 3 -CH group as the spacer, e.g., a methylene or an aliphatic chain, which is nonetheless not suitable for designing rigid molecular architectures.…”