A series of nonlinear optical chromophores based on the highly thermal and photostable tricyanovinylidenediphenylaminobenzene (TCVDPA) was synthesized and their thermal and optical properties were investigated. Modification of the TCVDPA chromophore with bulky groups provides reduction of dipole-dipole interactions and thus great improvement of the macroscopic electro-optic (EO) response of the polymeric materials obtained by incorporating these derivatives as a guest at high loading in polysulfone. The best result was obtained with chromophore C5, bearing fluorinated aromatic substituents, which shows a doubling of the EO activity at 30 wt% (25 pm V À1 at 830 nm) compared with the pristine TCVDPA. The bulkier the chromophore, the lower the induced plasticization effect (as much as 50 C difference on the T g attenuation). Furthermore, all chromophores in this study possess good processability and exhibit high thermal decomposition temperatures (highest T d ¼ 360 C).
Highly thermal and photostable nonlinear optical polymers were obtained by covalently incorporating the tricyanovinylidenediphenylaminobenzene (TCVDPA) chromophore to a polycarbonate backbone. NLO polycarbonates with different chromophore attachment modes and flexibilities were synthesized. In spite of the high loading levels (ranging from 33.1 to 39.8 wt%), the polymers exhibit T g s as high as 215 C, representing a significant improvement of over 100 C of the material T g compared with that of the guest-host system containing the same chromophore at similar high loadings. EO coefficients up to 33 pm V À1 at 830 nm were achieved, and a good temporal stability of the dipole alignment at 50 C was observed.
Introduction. Second-order nonlinear optical (NLO) polymers are being intensively investigated because of their potential application in high-speed electro-optic (EO) devices with very broad bandwidth and low driving voltage. [1][2][3][4][5] Covalent attachment of NLO chromophores to polymers backbones can effectively increase chromophore loading, prevent phase separation, and result in a better dipole alignment stability than the guest-host systems. 4,6 There are two major ways to achieve chemical incorporation of a NLO chromophore into a polymer. 4,7,8 One method is to functionalize the chromophore with suitable chemical groups to give a monomer that can eventually react to form a copolymer. [9][10][11] Although the so obtained sidechain NLO polymers have shown several advantages, such as a high-temperature alignment stability and good mechanical properties, this approach often requires tedious procedures for the synthesis of the appropriate chromophore-containing monomers. The other method is to covalently connect the chromophore, either directly or using a linker or spacer, to a prepolymerized macromolecule possessing a suitable pendent functionality for the attachment. [12][13][14] This procedure is particularly attractive for high NLO dyes, which are often prone to chemical degradation under the polymerization conditions. 15,16 While polycarbonates have widely been employed as a host material for NLO chromophores (amorphous polycarbonate, APC, in particular), thanks to good optical properties, high T g , and good processability, 5,17 to the best of our knowledge, there are no synthetic procedures that provide a convenient modular approach to attach NLO chromophores to the polycarbonate backbone.Moore and Brittain have reported a strategy to NLO polycarbonates in which first a chromophore was attached to the bisphenol functionality. 18 The chromophore was used to make cyclic carbonate oligomers which were eventually converted to polycarbonates via ring-opening polymerization in solution.Recently, we have reported a synthetic methodology to sidechain NLO polycarbonates, requiring the synthesis of donorcontaining dihydroxy monomers, followed by copolymerization and post-tricyanovinylation. 19 In this procedure, the polycarbonate backbones were achieved by condensation polymerization of equimolar amounts of a dihydroxy-containing monomer with the commercially available bis(chloroformates) of bisphenol A or Z. This class of compounds, however, is expensive, and not many derivatives are readily attainable, requiring the prior laboratory preparation in case monomers with different properties are needed. Furthermore, the general applicability of this
Direct waveguide definition of a negative photoresist (SU8) containing tricyanovinylidenediphenylaminobenzene (TCVDPA) as electro-optic (EO) chromophore, has been demonstrated for the first time. This was possible by utilising the chromophore low absorption window in the UV region allowing crosslinking of the host polymer by exposing to UV light followed by thermal curing. TCVDPA was modified by attachment of bulky side groups. This reduced the intermolecular interactions and resulted in an increased EO (r 33 ) coefficient.Introduction: Over the past decade the demand for telecommunication services and bandwidth has boomed. To handle this ever-increasing demand, high-speed electro-optic (EO) modulators operating over 100 GHz are required [1]. The currently used EO modulators based on LiNbO 3 are limited in bandwidth to 40 GHz, because at higher frequencies the velocity mismatch between the optical wave and the electrical travelling wave yields too large dephasing and consequently too short interaction lengths. To handle such high modulation frequencies a better performing material is required. Second-order nonlinear optical (NLO) polymers [2,3] were proposed two decades ago as useful candidates for this application. Though NLO polymers have the potential for high nonlinearity, the nonlinearity of the individual chromophores does not translate completely onto a macroscopic scale. This is because electrostatic intermolecular interactions lead to antiparallel clustering of the chromophores during electric field induced poling. These intermolecular interactions can be reduced by modifying the shape of the chromophore (making it more spherical) and thereby preventing their closer approach [4]. For long-term applications the chromophores should have a high photochemical stability at the operating wavelength and a high stability of the poling order at the operating temperature. TCVDPA has the highest reported photochemical stability [5]. In addition, its NLO figure of merit is higher than dimethylaminonitrostilbene (DANS) and disperse red (DR1). The difference between the glass transition temperature (T g ) of the polymer and the operating temperature, which determines the stability of the poling order, requires polymers with a high T g of about 200 C. When the NLO chromophores are incorporated in a photodefinable polymer, electro-optically active waveguides can be obtained by direct photodefinition. Compared with the reactive ion etching technique, this requires fewer processing steps and yields less sidewall roughness. In this Letter we report for the first time the direct photodefinition of an electro-optic polymer, i.e. TCVDPA in the SU8 host. Improvement of the poling efficiency by modifying TCVDPA with bulky side groups is also presented.
A laterally coupled microring resonator was fabricated by direct photodefinition of negative photoresist SU8, containing tricyanovinylidenediphenylaminobenzene chromophore, by exploiting the low ultraviolet absorption window of this chromophore. The ring resonator was first photodefined by slight cross-linking. Thereafter, poling (to align the chromophores) and further cross-linking (to increase the glass transition temperature) were simultaneously carried out. The material showed excellent photostability and the electro-optic modulation with an r33 of 11pm∕V was demonstrated at 10MHz.
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