Photochromic conjugated polymers

Among various photoresponsive compounds, dithienylethene (DE) derivatives are the most feasible photochromic materials due to their outstanding fatigue resistance, thermal stability, and reversible properties [65-67]. Addition of this photoresponsive moiety into an aromatic conjugated polymer is attractive as a method of dynamic control of luminescence through photoisomerization-driven... 

In addition to temperature and solvation effects, there are many other factors that may alter the UV-vis spectrum of conjugated polymers. Some examples of these are affinitychromism [19,65,185], electochromism [186], halochromism [187,189], and photochromism [189]. These effects can be deliberately employed in the design of novel devices such as optical sensors. 

Functionalised conjugated polymers such as polythiophenes were studied from the point of view of the detection and transduction of chemical and physical information into an optical or electrical signal. Their ionochromism (reversible change of colour in the presence of ions), photochromism (reversible change of colour on exposure to light), affinity chromism (tendency to colour change) and electroluminescence of polythiophene complexes with crown ethers and other solutions are discussed in detail [295]. 

Photochromic diarylethenes can be incorporated into polymers by following free-radical polymerization [75], polycondensation [76], Fridel-Crafts alkylation [77], or oxidative polymerization [78], The side-chain and main-chain homopolymers, copolymers, block copolymers, and jr-conjugated polymers synthesized by the above-mentioned methods have shown good photochromic properties in films and solution phase owing to the higher content of diarylethene chromophores in the polymer system compared to that in simple guest-host systems [79-81], Selected examples are illustrated in Figure 9.8. 

A number of reviews have appeared of topical interest. These include photoisomerism of azo dyes, ° photofunctional polysilanes,photochromic pigments, rare earth complexes, pressure sensitive paints, electron-transfer processes,electroactive dendrimers, chiral polyisocyanates, photodefin-able benzocyclobutene, photoconductive polymers,excited states in conjugated polyenes, photosensitive materials and polyazomethanes. ... 

Here, we have designed and synthesized multifunctional poly(bithienylene-phenylene)s with either racemic (Poly-9) (M — 14,000) or chiral moieties ((/ )-/ (S)-Poly-lO (Mn = 10,000, 8,000, respectively), which exhibit fluorescence, liquid crystallinity, and photoresponsive properties (Fig. 11.20). The polymers are composed of a 7t-conjugated main chain, poly(bithienylene-phenylene), which acts as a fluorescence moiety and mesogen core, and photochromic DE moieties [71, 72] are linked with racemic or chiral alkyl groups in the side chains. The DE photoresponsive moiety isomerizes between its closed and open forms upon irradiation of UV and visible light, respectively. 

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