SBAC polymer

Among the many types of processible NLO polymers, polyurethane with symmetrical substituted tris-azo dye with fluorinated alkyl units (PSTF for short) was selected as a waveguide material. PSTF is a novel third-order NLO main-chain polyurethane with tris-azo dye incorporated into the main chain with a fluorinated alkyl backbone [40]. This polymer is similar to the SBAC polymer family whereby a symmetrically substituted 7t-conjugated molecule was incorporated in a main-chain polymer. Azo dye is an effective NLO dye investigated by many researchers and the tris-azo dye is very special for NLO applications. Fluorinated alkyl units are expected to be effective for reducing the polymer... 

The shapes of the orbitals for the other molecules of Fig. 2 are shown in Fig. 5. Molecules B and C of Fig. 2 have donors at the both ends. For B and C in Fig. 5, HOMO-1 spreads somewhat into extremities, and electron-hole symmetry does not hold either between HOMO and LUMO nor between HOMO-1 and LUMO-i-1. These shapes are beneficial for %(3). However, the orbital HOMO does not spread into the extremities. This means that transition from HOMO-1 to HOMO does not have so much moment as that of SBA. The orbital shape for molecules B and C is not so good as SBA. With respect to the orbitals of the molecules E and F, both HOMO and HOMO-1 spread, and the electron-hole symmetry does not hold. These are beneficial for Molecules D, E and F, which have amino at both ends and have nitrogen atoms at the X positions of Fig. 1, are expected to have large third order susceptibilities. These results correspond well with the experimental fact that their measured X is large and as good as conjugated polymers. The x values of SBA and SBAC, which is dichloro SBA, are 1.0 X 10 esu and 1.3 x lO" esu. The X( ) of PU-STAD is 1.5 X 10 esu, which is a derivative of molecule F in Fig. 2. 

If the molecule is in a condition where the polarized excited state is stabilized owing to some polar circumstances, this further increases X - For the polymer including SBAC structure in the main chain, the x spectrum does not maximize at the peak point of the absorption spectrum but maximizes at a lower energy point than the peak in Fig. 8 of ref. 15. We guess this is because the amorphous structure of this polymer produces a nonsymmetric condition for each finite Jt-conjugation, which stabilizes the charge separation, at the low energy side of the exited state. 

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