Linda S. Sapochak

The design of new copolymers for x(3) applications

Abstract Several electroactive π-conjugated polymers have recently shown promising non-linear optical (NLO) properties. However, long conjugation sequences in such polymers as polyacetylene (PA), polythiophene (PT), poly( p -phenylene vinylene) (PPV) and poly(2,5-thienylene vinylene) (PTV) often result in solubility, processability and optical transparency problems that make their use in electro-optic devices difficult. In this paper it is outlined how copolymers in which oligomeric segments of PTV, alternating with saturated spacer units, can be synthesized and cast as optical-quality films for NLO applications. The design of oligomeric PTV monomers and preliminary NLO characterization of the copolymers are also described.

Development of materials with enhanced optical non-linearity by control of ultrastructure

Abstract Copolymers incorporating rigid electroactive moieties and flexible segments have been synthesized in an effort to develop non-linear optical materials which can be processed into optical quality films. A variety of coupling linkages have been employed including ether, ester, amide, imine and azo linkages. Among the most attractive materials examined in this survey are heteroaromatic ladder and tetraazaannulene copolymers which yield optical non-linearities (ratioed to optical loss), χ (3) α of 10 −12 −10 −13 esu cm −1 and have desirable auxiliary properties of high laser damage threshold and fast optical switching (t ps for three-ring copolymer). Electron donating and withdrawing groups are conveniently incorporated and these have been observed to influence optical non-linearity. The copolymer approach yields linear optical spectra characterized by sharp band edges thus optimizing the window of transparency. Finally, it is noted that this approach yields excellent control of solubility and solution viscosity necessary for spin casting in the fabrication of thin films of uniform thickness.

Recent advances in the synthesis and characterization of nonlinear optical materials: second-order materials

Abstract A major problem in utilizing second-order organic materials for device applications is the requirement for the assembly of these chromophores into a stable, noncentrosymmetric lattice. For certain applications, such as frequency doubling, a periodic noncentrosymmetric lattice may be desirable. In this presentation, we discuss the synthesis of such organic polymeric lattices and evaluation of modulators and doublers fabricated from resulting materials. The general approach is to develop soluble, processible precursor polymers which can be transformed into stable noncentrosymmetric lattices by electric field poling and subsequent photoinduced or thermally induced solid state crosslinking reactions. Photo-processing is utilized to generate periodic noncentrosymmetric lattices for quasi-phase-matched second-harmonic generation.

Synthesis and incorporation of ladder polymer subunits in copolyamides, pendant polymers, and composites for enhanced nonlinear optical response

Several electroactive polymers, such as polyacetylene, polythiophene, poly [p-phenylene vinylene] and poly [2,5-thienylene vinylene] have shown promise as NLO-active materials over the past few years. However, as several theoretical and experimental research groups have pointed out in recent publications and symposia, it is not evident that long conjugation lengths are necessary for enhanced (chi) (3) activity. As recently demonstrated, copolyamides which incorporate polyenylic or PTV oligomeric repeat units show (chi) (3)/(alpha) values of ca. 10-13 esu-cm at 532 nm(band-edge). In this paper, the authors discuss how ladder subunits related to the electroactive polymers POL and PTL can be incorporated into polymer films as (a) copolymer repeat units, (b) pendant groups attached to poly [p-hydroxystyrene] and (c) guest-host composites in polycarbonate. Sharp optical absorptions are found in all cases as well as promising (chi) (3) properties.

New copolymers for nonlinear optics applications that incorporate delocalized pi-electron subunits with well-defined conjugation lengths

During the past three years it has become more evident that long conjugation sequences in electroactive materials may not be a stringent requirement for high third order nonlinear optical (NLO) activity. Since long conjugation lengths in these materials often make them difficult to process, the resulting insolubility often precludes the formation of optical quality films for device applications. The incorporation of shorter electroactive segments alternating with flexible non-active spacers may allow high NLO activity coupled with good optical film forming capability. In this paper we would like to present several approaches to copolymer design which incorporate various electroactive oligomer segments with well-defined conjugation lengths. The control one obtains in this appmach allows the design of sharp optical windows, and the ability to tailor absorption characteristics to particular frequencies.

Multifunctional materials: new mechanisms for NLO effects

Multifunctional properties of nonlinear optical chromophores are discussed both in terms of a given chromophore exhibiting more than one type or mechanism of optical nonlinearity and in terms of a chromophore exhibiting useful auxiliary properties. For materials exhibiting more than one type of mechanism of optical nonlinearity, the concept of pulse-controlled optical nonlinearity is introduced and discussed. An analogy is drawn to multidimensional nuclear magnetic resonance studies which are useful in systematically elucidating excited state dynamics. Practically, pulsed control of optical nonlinearity provides a means of enhancing and modulating nonlinear optical phenomena. The photochemical reactivity of nonlinear optical chromophores is discussed in terms of fabricating ordered lattices appropriate for the development of integrated circuits and the realization of specific effects such as quasi-phase matching in second harmonic generation.

New Copolymers for Nonlinear Optics Application which Incorporate Electroactive Subunits with Well Defined Conjugation Lengths

Over the past five or six years, rapid advances have been made in the field of photonics, or the manipulation of light by light. Although organic polymers have been generally regarded as insulators in the electronics industry, research advances in the area of electroactive materials have shown that polymers such as polyacetylene can achieve metallic conductivity approaching that of copper when oxidized or reduced chemically or electrochemically (doping). More recently, it has been recognized in our laboratory and others that electroactive materials also have exceptionally high optical nonlinearities. Research on these materials holds the promise that they indeed may be suitable for the eventual design of many nonlinear and electro-optic devices, including an all-optical computer.

Development of Materials with Enhanced Optical Nonlinearity: Theory and Practice

Abstract Synthetic schemes have been developed for systematically incorporating electroactive it-electron polymer segments together with saturated alkoxy segments into copolymers which exhibit sufficient solubility in common solvents to facilitate characterization and to permit processing of these copolymers into optical quality films. This approach has permitted a rapid survey of the optical nonlinearity of a variety of electroactive structures ranging from phenylpolyenes to ladder-type oligomers. Studies on materials prepared by copolymer synthesis have been correlated with studies of materials with electroactive units incorporated as pendant groups to non-active polymer backbones and with studies of materials where electroactive molecules are incorporated as dopants into non-active polymers to form composite materials. Incorporation of electroactive oligomeric units into polymer systems affords significant advantages in terms of processing and can be adapted to the study of structure/function relations...

Asymmetrical Diphenylpolyene Pendant Polymers for Nonlinear Optical Activity

Recent activity in the development of nonlinear optical (NLO) materials with high second order susceptibilities has prompted the development of a wide variety of pendant polymers which possess desirable properties for device development, including high T g minimal relaxation of the poled matrix, and high laser damage threshold. Ideal candidates for such systems are asymmetrically substituted oligomers of polyacetylenes such as dimethylaminonitrostilbene (DANS) and corresponding higher order oligomers. We report here a preliminary study of the synthesis of asymmetrically substituted donor/acceptor diphenyl-capped polyenes and thienylene vinylene oligomers attached as pendant moieties on polyvinylphenol (PVP) for second harmonic generation.

Incorporation of Ladder Polymer Subunits in Formal Copolymers for Third Order Nlo Applications

Ladder polymers such as POL and PTL have been regarded as promising candidates for the third-order nonlinear optical (NLO) applications due to their highly conjugated planar pi-electron framework and high thermal stability. However, their lack of processibility has generally precluded their use. Over the past three years, however, we have demonstrated that five ring ladder subunits can be incorporated in formal 1:1 copolymers, or as pendant substituents on polymer backbones such as polyvinylphenol1,2. These materials have extremely interesting χ(3) properties related both to the magnitude of response and the decay mechanism observed during the degenerate four wave mixing process. In this paper we will explore how substituent group choice in the ladder moiety can enhance both χ(3) as well as provide improved processibility.