Organic NLO Polymers. 2. A Study of Main-Chain and Guest-Host NLO Polymers: NLO-phore Structure Versus Poling

Abstract

Several new dipolar main-chain (2) nonlinear optical (NLO) polymers were prepared. The NLO-phores, based on alkoxy substituted -cyanoacrylates, were also placed as monomeric guests within a poly(methyl methacrylate) host. Polar alignment of the NLO-phores by corona poling and their relaxation behavior was monitored by detecting the optical signal resulting from the second harmonic generation. The study revealed that two dipolar rigid-rod main-chain NLO polymers (NLOPs), having solubilizing side chains, were not responsive to alignment by corona poling. We found that each main-chain NLOP prepared in the study showed a strong resistance to alignment, whereas virtually the same NLO-phore as a guest within a polymer host responded well to corona poling. When small variations were made in the structure of the NLO-phore, it was found that when hydrogen-bonding groups are rigidly coupled to the NLO-phore they were very effective for retaining polar asymmetry induced by poling and induced no deleterious effects on the alignment process. For main-chain NLOPs, it appears for optimum alignment the bonding axis and the polar axis should not be parallel.

Second-order non-linear optical polymers

“…Köhler et al 12,13) studied the relaxation of electric field induced polar orientation in main-chain polymers. Stenger-Smith et al 65,66) , Lindsay et al 67) , Wrigth et al 68,69) and Liu et al 70) also synthesized main-chain polymers, but the reported second-order susceptibilites were low (0.17 pm/V). A polyurethane main-chain polymer with dialkylamino sulfonyl azobenzene incorporated in the main chain was studied by Xu et al 71) They measured a d 33 (-2 x; x, x) value of 40 pm/V (T g not given, poled at 115 8C, excitation at 1 064 nm).…”

Optical alignment of organic dopants in a solid gel matrix: dispersed and grafted rhodamine B molecules

“…Therefore, the idea arose [6][7][8] not to simply disperse these molecules in the matrix but to graft them on the inner surface of its pores through covalent bonds. In a similar way, recent works on doped organic polymers have proven the great interest of such a grafting [9] for nonlinear optical properties. In our case, this ought to allow much higher concentrations in dye molecules in the gel without segregation, and thus should lead to higher birefringences.…”

“…Here the spacer is the chain --(CHz)3--NH--CS--NH--, which length seems large enough to ensure the movements of the grafted rhodamine B molecule. It is important here to point out the importance of the flexibility of the spacer for the alignment of the dopants, as previous studies led on doped organic polymers have established it [9].…”

“…The spacer we envisaged in this paper, --(CH2)3 --NH---CS--NH--, may not have the optimal structure in order to insure both a maximal alignment of the dopants along the excitating field and a maximal persistence of this alignment. Recent works led on doped organic polymers [9] showed a strong influence of the structure--and especially the length--of such a spacer on the relaxation of the dopants, and may be extended to the case of inorganic gel matrices. Furthermore, thanks to the strong increase in potential doping concentration, these encouraging results may now be extended to the case of film-deposited gel matrices for guided optics.…”

Synthesis of novel poly(vinyl ether)s containing the oxybenzylidenemalononitrile group as a nonlinear optical chromophore, and their electro‐optic properties

“…There are tremendous challenges in the design and synthesis of polymers with large NLO effects. Polyesters,8–10 polyurethanes,11–15 polyamides,16, 17 and poly(phenylene ethynylene)s18 containing a chromophoric main chain have been prepared. Various polymers with NLO‐chromophores in the side chain, such as poly(meth)acrylates,19–23 polystyrene24 and polyimides25–28 have also been reported.…”