In this paper several new organometallic polymers have been prepared. Structure-property relationships for local polymer mobility and the net orientation of the organometallic nonlinear optical (NLO)-phores have been investigated using second harmonic generation (SHG). The methacrylate organometallic derivatives {775-C5H4CH202CC(CH3)=CH2}Fe{j)s-C5H4CH=C(CN)X) [4a, X = p-CeHjBr; 4b, X = 4-pyridyl; 4c, X = CN; 4d, X = C02Et] and {t5-C6H4CH=C(CN)C02(CH2)202CC(CH3)=CH2|Fe|7,6-C5H5} (7) were prepared and polymerized with methyl methacrylate (5/95, mol/mol) to afford copolymers 8a-d and 9, respectively. Comonomer {i)s-C6H4CH=C(CN)C02(CH2)20H}Fe{i;6-C5H4CH2C)H} ( 5) was synthesized and reacted with 1,6-diisocyanatohexane to yield a main-chain NLO organometallic polyurethane 10 (Mn = 7600, Tm = 176 °C). In addition, a poly(methyl methacrylate) guest-host film of NLO-phore 5 was prepared. Corona poling and SHG measurements were made under a variety of carefully controlled experimental conditions. In the case of the covalently bound ferrocenyl NLO-phore, temporal stability was greatest for the smaller acceptor group CH=C(CN)2 (t.e., copolymer 8c). The rate of relaxation for copolymer 8d was faster than that for 9, indicating that the point of attachment on the ferrocenyl NLO-phore to the polymer backbone was an important consideration. It was found that physically aging the organometallic polymers prior to poling produced samples which displayed a smaller initial SHG signal; however, the signal was significantly more stable for a longer time. The guest-host system using NLO-phore 5, with its multiple hydrogen-bonding sites, was observed to have very good long-term temporal stability. The guest-host polymer was poled negatively and showed enhanced temporal stability in comparison to a positively poled sample. The organometallic main-chain copolymer 10 responded well to poling but had concomitant decomposition, leading to an underestimation of orientational stability.
A detailed structural analysis of several ferrocene-based nonlinear optical (NLO)-phores was done by X-ray diffraction. Structures were reported for (jj5-CbH5}{)j6-C5H4CH=C(CN) (R)}Fe[la,R = CC^Et; lb, R = CN; lc, R = 4-pyridyl; Id, R = 4-bromophenylJ. The study illustrated that electron-withdrawing groups favor and control the planarity of the -system. Through selective functionalization of the cyclopentadienyl rings of ferrocene, new monomers, namely, {ij5-C5H4CH20(CH2)nOH}{))5-C6H4CH=C(CN)C02-Et}Fe ( 5) and {tj6-C5H4CH20(CH2)"02CCH2CN}{775-C6H4CHO}Fe [6, n -6; 8, = 1], were prepared in the study. Monomer 5 was suitable for Lewis acid catalyzed transesterification/polymerization using TiiOCtHgh, and 6 and 8 were appropriate for a Knoevenagel polycondensation. The transesterification polymerization resulted in formation of an intractable polymeric material of unknown structure. The homopolymerization of 6 by the Knoevenagel technique afforded the desired polymer 9a, albeit in low molecular weight \Ma = ~6800}. The polymer was characterized by gel permeation chromatography and spectroscopic data. A major byproduct in the polymerization was the macrocyclic lactone 10a produced from an intramolecular Knoevenagel condensation. The lactone structure was confirmed by single-crystal X-ray diffraction.
The development of materials for use in nonlinear optical (NLO) devices has become a vigorous area of research in the chemical community.1 Several chemical compositions have been proven to be effective NLO materials. Polymeric materials are very attractive because of their processability which will lead to facile device fabrication.2
This paper describes preliminary work exploring the feasibility of preparing high-performance nonlinear optical (NLO) materials based on the poly@-phenylene (PPP) backbone. Three new monomer/NLO-phores of the general formula: 4-RS0,C,H4C= C(4-XC6HS (where R = 2,5-dichlorophenyl; 2a, X = H; 2b, X = OCH,; 2c, X = N(CH,)d were synthesized and then homopolymerized using catalytic nickel and stoichiometric zinc to produce the poly@-phenylenes), 3 a-c, respectively, as lowmolecular-weight materials (number-average molecular weight a,, = 1 800-6000). NLOphores 2 b-c and low-molecular-weight oligomers of 3c were dispersed in a poly(methy1 methacrylate) (PMMA) host. Spin-cast films of these guest-host systems were subjected to corona poling above the glass transition temperature Tg. Following poling, both monomer NLO-phore/PMMA guest-host systems displayed optical nonlinearity with second-order nonlinear optical susceptibility x(') values of 1.7 pm/V and 0.9 pm/V for 2c and 2b, respectively. Both systems exhibited good temporal stability at room temperature, with about 12% loss in second harmonic signal over more than 100 h. However, the oligomeric material 3c dispersed in PMMA showed a smaller NLO signal when poled above Tg.Attempts to induce dipolar asymmetry in the homopolymers 3 b and 3 c were unsuccessful. The observed response during poling and the relaxation of the chromophore orientation following poling, have been discussed in terms of structure and composition of these systems.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.