Photo-orientation symmetry

Section 3.2 of this chapter recalls the pure photochemical point of view of photoisomerization of azobenzene derivatives. Section 3.3 discusses the theory of photo-orientation by photoisomerization and gives analytical expressions for the measurement of coupled photoisomerization and photo-orientation parameters. Sections 3.4 and 3.5 review observations of photo-orientation in azobenzene and push-pull azobenzene derivatives, respectively. Among other things, these sections address photo-orientation in both cis and trans isomers and discuss the effect of trans<->cis cycling, i.e., the photochemical quantum yields, on photo-orientation. Section 3.6 discusses the effect of the symmetry of photochemical transitions on photo-orientation in spiropyran and diarylethene-type chromophores. Finally, I make some concluding observations in Section 3.7. 

When the analysis of photo-orientation is performed at a wavelength different from the irradiation wavelength, the symmetry of the molecular transitions in both A and B isomers can be found. Indeed, setting n=0 in Equation 3.9, yields the following relation for the photostationary state of irradiation ... 

Photo-Orientation Dynamics and Transitions Symmetry 89 Conclusion 96... 

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