Chromophores octupolar

The search for efficient NLO-phores includes also the design of octupolar derivatives [40, 70a]. The advantages associated with this alternative class of NLO-phore include an improved nonlinearity-transparency trade-off and more facile noncentrosymmetric arrangement in the solid state due to the absence of dipolar moments. To this end, the 3-D chromophores 135 and 136 with C3 and D2 (approximate T) symmetry, respectively (Scheme 4.39), have been prepared according to classical synthetic routes [73a]. 

Many octupolar chromophores have threefold symmetry based around 1,3,5-substituted benzene or triazine cores an example [66] is shown in Fig. 11.8 and this type of chromphore has more recently also been used in extended dendrimeric structures [67]. However, other non-centrosymmetric cores have been used, for example, four-coordinate tetrahedral tin centers [68],... 

Zojer et al.192 have discussed the limitations of the essential-state model in calculating the TPA of bis(dioxaborine-)-substituted chromophores. Lukes and Breza193 have made an AM1-ZINDO/SOS study of spirobifluorene type molecules. Jha et al.194 have employed their method of obtaining model exact solutions in the PPP approximation to calculate TPA cross-sections for trans-stilbene and 7,8-disubstituted stilbenes. Zhou et al 95 and Liu et al.196 have studied one and two photon absorption in octupolar compounds using DFT and ZINDO/SOS methods and the group has applied similar methods to trigonal dehydrobenzo[l8]annulenes.197... 

D. Octupolar/ Propeller Shaped Chromophores with Large Two-Photon Absorptivity... 

Figure 3.51. Schematic presentation of CT in the excited state of a C-ih chromophore along the three axes favored for CT in octupolar chromophores q0 corresponds to the amount of charge transferred in each individual arm [left (D-7t)3-A chromophore right (A-7i)3-D chromophore].

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