Organic Photochemistry Some Case Studies

Through the analysis of some selected case studies, we hope to establish the following ideas, which appear to be general  

Photochemistry of conjugated hydrocarbons can be rationalized by the common electronic and molecular structure of the surface crossing between a covalent excited state and the ground state. 

Photochemistry of azoalkanes and enones is dominated by intersections of n-n and n-n states with the ground state as well as by the intervention of the triplet manifold. 

Photochemistry of protonated Schiff bases is also based on conical intersections however, the excited state is ionic and corresponds to an intramolecular charge transfer state thus the theoretical aspects of the problem are distinct from polyenes. 

The quantum yield in the radiationless decay and competitive photoproduct formation process in cyclohexadiene/cZc-hexatriene (1) system is controlled 

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Mechanistic Organic Photochemistry Some Case Studies 121... 

The photochemistry of small molecule LC materials has been an active area of research for many years and has been reviewed recently [9]. The photochemistry of LC polymers, per se, has received much less attention although two brief reviews have appeared [5,10], and there has been a considerable effort to apply some simple photochemical transformations such as trans-cis photoisomerization, to the development of practical devices [1-6]. This section is divided into three parts. In Part A, chromophore aggregation, which seems to be important in almost all the cases in which careful UV-Vis and/or fluorescence studies of films of pure LC polymers have been made, is explicitly discussed. Part B is devoted to a thorough review, organized by chromophore type, of the photochemistry and related photophysics of LC polymers. No attempt has been made to extensively cross-reference the work on LC polymers to the hundreds of papers and reviews on analogous non-LC compounds. However, when it seemed particularly appropriate or interesting, experiments related to optical applications of the photochemistry of LC polymers are briefly described. In Part C, a few experiments are described in which a classical photophysical method, fluorescence spectroscopy, is used to probe the microstructures of some LC polymers. 

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