Adriana Galvan-Gonzalez

Effect of temperature and atmospheric environment on the photodegradation of some Disperse Red 1-type polymers.

The photodegradation of the azobenzene chromophore DR1 {4-[N-ethyl-N-(2-hydroxyethyl)amino]-4(?)-nitroazobenzene]} incorporated as a side chain or as a guest in a poly(methyl) methacrylate host has been evaluated as a function of wavelength, temperature, and the atmospheric environment. The effects of these variables on the lifetime of DR1-based electro-optic devices is quantified.

Systematic behavior of electro-optic chromophore photostability

The wavelength dependence of the one-photon absorption-induced photodegradation rate has been measured from the visible to the near IR for a variety of electro-optic chromophore-doped polymers. Systematic behavior is identified. The lifetime of the electro-optic activity is found to increase exponentially over 4-6 orders of magnitude for wavelengths ranging from peak of absorption, typically in the visible, to ~1000 nm. Many popular chromophores developed for electro-optics over the past 10 years are compared.

Photostability of electro-optic polymers possessing chromophores with efficient amino donors and cyano-containing acceptors

The photostability of various electro-optic active guest–host polymers, doped with chromophores that possess very efficient cyano-containing acceptors and dialkyamino- or diarylamino-benzenes, and also their extended thiophene analogs as bridging structures, has been investigated over a broad wavelength range in the near infrared and the visible. A variation of over 2 orders of magnitude was found in the probability that an absorbed photon will lead to a photodegraded chromophore. The most photostable chromophore contained a tricyanovinyl acceptor and a diarylaminobenzene bridge unit.

Photodegradation of selected π-conjugated electro-optic chromophores

The photodegradation properties of six electro-optic chromophores in guest-host polymer formats were measured as a function of wavelength throughout the visible and up to 1.3 μm in the near infrared. The chromophore structure was varied to provide insight into its relationship with photostability.

Photostability enhancement of an azobenzene photonic polymer

We have found that the presence of a methacrylate group on an azobenzene electro-optic chromophore can provide an enhancement in photostability of up to one or two orders of magnitude. Systematic studies involving the change in chromophore structure and atmospheric environment indicate that the photostabilization is due to antioxidant action by the unsaturated functional group.

Local and external factors affecting the photodegradation of 4N,N′-dimethylamino-4′nitrostilbene polymer films

The photodegradation of the electro-optic chromophore 4N,N′-dimethylamino-4′nitrostilbene was investigated as a function of wavelength, temperature, local atmosphere, and local molecular environment, i.e., attached as a side chain to a polymer or dissolved as a guest in a host polymer.

Material glass transition temperature, device thickness, and operational temperature effects on absorption of electro-optic polymer films

In chromophore doped materials, the trade-off between nonlinear coefficients and absorption is a critical issue. In particular, X(2):X(2) cascading based applications at 1.55 micrometers impose stringent conditions on the absorption at the second-harmonic wavelength. Transmission spectroscopy through a thin film does not provide sufficient resolution to measure the absorption coefficient on the red side of the main absorption band. However, assuming Voigt profiles, it is possible to extrapolate the absorption coefficient in the near infrared (NIR) from the main electronic resonance. We report on the dramatic impact of the host polymer matrix on the near infrared absorption of azobenzene chromophores. The effect is directly correlated to the host polymer glass transition temperature. The case of hybrid sol-gel material is also discussed. In particular, we present here an interesting correlation between the poling temperature and some spectroscopic properties. This correlation and thermo- spectroscopic measurements lead us to define an effective Tg in the sol-gel system. We also report on film thickness dependent absorption properties.

Systematic wavelength dependence of the photodegradation of polymers doped with electro-optic chromophores

Summary form only given. There have been a number of recent breakthroughs in polymer photonics resulting in record performance of electro-optic modulators, photorefractive efficiency, etc. A common feature to many of these applications is an electro-optic active chromophore, usually based on a strong charge transfer mechanism. Such molecules are also frequently used for writing permanent index changes via a variety of photobleaching mechanisms near their absorption maximum where they are not photostable. A critical question is the wavelength dependence of the photostability and its value at device operating wavelengths. There have been a few reports on photostability but no systematic study of this effect. In this paper we discuss an appropriate photostability figure of merit, its wavelength dependence which appears to be universal, and the values required for multiyear device operation.

Lifetime of electro-optic polymeric devices

Polymeric materials are promising for use in various optical devices. However, the lifetime of chromophore-doped polymeric optical devices is limited by the photodegradation of the active chromophore that provides the material system its useful optical properties. The term photodegradation covers the chemical transformation that occurs in the dyes while in the excited state or during relaxation, following photon absorption. Such transformation leads to the creation of new species, generally optically inactive, and decreases the concentration of the active chromophore, lowering the material and device efficiencies. One can model the rate of the transformation by introducing the quantum efficiency of the degradation reaction, B/sup -1/. Thus B is the average number of excitation cycles a given chromophore, in given conditions, can undergo before becoming inactive. In order to determine new classes of chromophore doped polymer materials fulfilling these requirements, it is necessary to quantify the impact that different parameters, such as different chromophores, polymer matrix structures, and external physical conditions, have on this B value. We are accomplishing this goal by systematically characterizing the photostability of different electro-optic dye-doped polymer materials.