Phase rebuilding mechanism

Keywords Gas-solid reaction Solid-solid reaction IntracrystaUine reaction Phase rebuilding mechanism Solid-state cascade reaction 100% yield... 

ElZ isomerizations are usually not expected in the solid state. They have been widely studied in solutions or in liquids. This includes thermal, catalytic, and photolytic processes and ElZ isomerization was also observed in competition with biphotonic excimer laser photodecompositions [47]. Most of the ElZ isomerizations in the solid state have been photo chemically observed [48], but mostly not as uniform quantitative reactions. If these isomerizations cannot be performed under selective conditions of irradiation (an exception is 83/84) [49], the only chance to have these reactions uniform with 100% yield is a very efficient isomerization (according to the phase rebuilding mechanism) that leads to an isomeric product with heavily interlocked crystal lattice. Under such circumstances side reactions of the substrate and photoconversions of the product are prohibited (including the back reaction, of course). Four favorable cases... 

Chloroanthracene. Single crystals of 7c provide particularly beautiful nanostructures if their main and side faces are irradiated to give 8c and if this reaction is probed with AFM [6, 8, 23]. Figure 16 (see color plates) shows the pronounced differences of the phase-rebuilding mechanisms on different faces, even though those could not be crystallographically specified because of lack of X-ray structural data. 

It is of some interest to compare these results with those of 9-methylan-thracene 7b, whose photodimerization has been termed topochemically allowed (d = 3.87 A [22])]. If the main surface of 7b (100) is irradiated, AFM scans floes initially and upon continuation of the irradiation these increase [8]. This shows that there are also long-range molecular transports and that phase rebuilding again governs the process. In any case, there is no special mechanism if a reaction may be termed topochemically allowed by previous convention (see Section C). 

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