Biphotochromic Systems

Applying one of the four synthetic approaches (a-d) (see Sections 6.2.1.1 to 6.2.1.4) in combination with the same or a second approach, can lead to biphotochromic systems.30-33 In principle, these are symmetrical systems such as DHI-DHI and unsymmetrical systems such as DHI-a-DHI-b DHI, photochromic systems-c are possible. 

In the case of regio- or stereoselective reactions of 9 —> 7 as well as in biphotochromic systems (24 -> 23), the kinetics become more complicated (see Refs. 30 and 33). The 11/2 values can be used as a rough order for a structure-fade rate relationship. Again, to analyze the data in a simple way, DHI 7 is divided into... 

The combination of two photochromic units as in molecules 30, 49, 50 (Scheme 23) can result in very interesting materials. Irradiation of the mixed biphotochromic system 30 leads to a colored form absorbing in the infrared. Thus IR-sensitive materials become available. A detailed description of this new material is given in Ref. 34, 65. The charge, distribution in the colored ring open form can be schematically represented as shown in Scheme 26. 

Other photochromic systems are using the ring opening/ring closing of thienyl pyrans. Examples are 134 <20060L4931> as a biphotochromic system or 135. 

Fiigoh M, Mehl H (2005) Multiple addressing in a hybrid biphotochromic system. Angew Chem Int Ed Engl 44 5048-5052. doi 10.1002/anie.200462575... 

Biphotochromic systems containing (1) two DHI-molecules, " (2) a DHI- and a salicylideneanil," and (3) DHI-spirooxazine have also been prepared. 

A typical system for an unsymmetrical photochromic compound is molecule 32. It is prepared by reaction of 21 with pyridosaHcyHdenanil. Recently, unsymmetrical biphotochromic molecules combining spiroxazine-and spirodihydroindolizine structures have been prepared." ... 

Ortica, E, Levi, R, Gugiehnetti, R.J., Mazzucato, U., and Favaro, G., Photokinetic behaviour of biphotochromic supramolecular systems. 2. A bis-benzo-[2//]-chromene and a spiroox-azine chromene with a (Z-)ethenic bridge between each moiety, /. Photochem. Photobiol, A Chem., 139, 133, 2001, and the references therein. 

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