Porphyrin liquid-crystal properties

Second, in addition to the above, the fact that many expanded porphyrins are highly colored makes their use as dyes an obvious possibihty. Here their planar nature makes them particularly attractive as chromophores for use in liquid crystals and optical data storage applications. Also, these properties could make them of interest as photo-sensors in various clinical or pseudo-clinical situations. For instance, the high affinity by certain sapphyrins for enveloped viruses and cholesterol rich liposomes suggests that expanded porphyrins could be used to detect and/or destroy a variety of unwanted biological targets, including arterial sclerotic plaque. 

Phthalocyanines and metallophthalocyanines have been intensively studied as discotic liquid crystals,but porphyrins have received less attention. The first examples of porphyrin discotic phases were based on naturally occurring uroporphyrins but showed a very narrow discotic LC range. However, octa—substituted porphyrins can show discotic meso-phases over a broad temperature range, the LC phase being stabilised by metal insertion into the porphyrin, e.g. zinc. These materials are organic semiconductors whose LC properties allow them to form highly ordered thin films in the solid state. Emission, excitation and absorption spectra in... 

Porphyrins, phthalocyanines, crown ethers and their complexes, modified by long-chain peripheral substituents, exhibit attractive properties as liquid crystals [80-88]. The complex [Cu(L263)] forms part of a thermoreactive composition used for the manufacture of polymer coatings, glues and hermetic compositions, and for shaping various articles [89]. 

The Phthalocyanine discogens (Scheme 2) have been extensively studied and their synthesis and properties are well documented in books and articles [20, 21] and references therein. These, together with the poqthy-rins and metal-porphyrins form phases which typify narrow band-gap columnar liquid crystals [21-24]. 

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