INDEX trans effect

The columns are indexed by the three states of bond i, the rows are indexed by the three states of bond i—1, and the order of indexing is t, g+, g. The statistical weight denoted by cr, which is approximately exp (-250/T), is the first-order weight of a gauche state relative to a trans state. The second-order interaction, which arises from the pentane effect where a bond pair is g gT, is weighted by to, which is approximately exp (-1000/T). 

Figure 18. Evolution of the indices of refraction in the plane of the LBK (Pj.ioi 156 monolayers) structure n, n ), and in the perpendicular direction (n ) under different conditions. The first column refers to the sample before any irradiation (New), and the columns labelled UV or B refer, respectively, to the sample after UV (360 nm) and blue-light (450 nm) irradiations. The high anisotropy shown in the columns labelled New or B indicates a highly optically anisotropic LBK structure. The columns labelled UV show a much less optically anisotropic structure. The evolution of the mean refractive index n under successive UV and blue-light irradiations suggests that the azo-molecules are switched between the two conformations (e.g., cis and trans) without a photobleaching effect.

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