Second dipolar chromophores

One key property of pyridylphosphole ligands is their heteroditopic nature. They possess two coordination centers with different stereo-electronic properties, which, in accordance with Pearson s antisymbiotic effect [42a], can control the orientation of a second chelating ligand in the coordination sphere of a square-planar d8-metal center [42b]. This property has been exploited in order to control the in-plane parallel arrangement of ID-dipolar chromophores [42d]. Phospholes... 

For dipolar chromophores that are the subject of this chapter, only one component of the molecular hyperpolarizability tensor, Pzzz, is important. Thus, the summation in Eq. (8) disappears. Electric field poling induces Cv cylindrical polar symmetry. Assuming Kleinman [12] symmetry, only two independent components of the macroscopic second-order nonlinear optical susceptibility tensor... 

Clearly, a requirement for device quality second-order nonlinear optical materials is a noncentrosymmetric dipolar chromophore lattice. There are several ways by which such lattices have been achieved. With all methods, a force must... 

For the experimental determination of the second-order first hyperpolarizability, some sort of non-centrosymmetry has to be present in the solution. This can be achieved by applying a static electric field over a solution of neutral molecules with dipolar chromophores. Implicitly, this description limits the applicability of this Electric-field-induced second-harmonic generation (EFISHG) technique ... 

Although Zyss and Ledoux [32] have proposed the development and exploitation of octupolar chromophores, device development exploiting second-order optical nonlinearities has largely focused on dipolar chromophores of the form... 

In the EFISH technique (Electric Field Induced Second Harmonic) a solution of the (dipolar) chromophore under consideration is put into a uniform static electric field, obtained for example with parallel metal electrodes. In practice, instead of putting metal electrodes in the solution, the solution is put in a wedge shaped cell bounded by glass windows at which metal electrodes are applied [8]. Owing to the dipolar nature of the chromophores, they statistically orient under the electric field and the whole solution becomes a second order NLO-active polar medium. When a laser radiation crosses the solution, second harmonic radiation is generated and collected. By comparison with a standard nonlinear medium (usually a quartz slab) it is possible to extract the value of the dot product of the chromophore. As we have... 

Yu J, Cui Y, Wu C, Yang Y, Wang Z, O Keeffe M, Chen B, Qian G (2012) Second-order nonlinear optical activity induced by ordered dipolar chromophores confined in the pores of an anionic metal-organic fi amework. Angew Chem Int Ed 51 10542-10545... 

Dipolar chromophores must be assembled into a noncentrosymmetric lattice to translate molecular optical nonlinearity to maaoscopic electro-optic (EO) aaivity, which is one example of second-order NLO properties. The EO coefficient in units of pmV , rs3, is the principal element of the linear Pockel s EO effect tensor and denotes the magnitude of refractive index shift (Ai ) obtained for an applied low-frequency electric field. This... 

In Fig. 3, the values for the electron-number-related static hyperpolarizability fiJN312 obtained for these ionic chromophores (open symbols) have been compared with the same values for the best dipolar, neutral chromophores reported so far (diamonds).31 32 These chromophores, with a reduced number of electrons N equal to 20, have dynamic first hyperpolarizabilities approaching 3000 x 10 30 esu at a fundamental wavelength of 1.064 pm, in combination with a charge transfer (CT) absorption band around 650 nm. It is clear that at this point, the neutral NLOphores surpass the available ionic stilbazolium chromophores for second-order NLO applications, however, only at the molecular level. The chromophore number density that can be achieved in ionic crystals is larger than the optimal chromophore density in guest-host systems. 

The challenges outlined above still await a solution. In this section, we show how some of the theoretical limitations employed in traditional formulations of the band shape analysis can be lifted. We discuss two extensions of the present-day band shape analysis. First, the two-state model of CT transitions is applied to build the Franck-Condon optical envelopes. Second, the restriction of only two electronic states is lifted within the band shape analysis of polarizable chromophores that takes higher lying excited states into account through the solute dipolar polarizability. Finally, we show how a hybrid model incorporating the electronic delocalization and chromophore s polarizability effects can be successfully applied to the calculation of steady-state optical band shapes of the optical dye coumarin 153 (C153). We first start with a general theory and outline the connection between optical intensities and the ET matrix element and transition dipole. 

The work reported here has shown that inclusion complexation of organic and organometallic chromophores by thiourea, TOT and cyclodextrins can induce second harmonic generation capability in the polar crystals which result, even when the original bulk materials are themselves incapable of SHG. Structural evidence has been presented to show tht the solid state inclusion structures are acentric, and a simple electronic picture t0 the polarization response of these materials within the two-state modeP ° has been discussed. In an earlier section we remarked that of the many complexes we have made, only one has NOT been acentric. This result was not anticipated. We postulate that it is a natural tendancy in such materials, rather that an exception. If we consider a dipolar molecule in isotropic solution, we can imagine that if it were to aggregate, it would do so in a head to tail fashion in order to minimize electrostatic repulsion. The situation is illustrated in Scheme 3. The arrangement that would result is centrosymmetric. 

Second order optical nonlinearity can be induced in polymeric systems containing dipolar (donor-acceptor) chromophores. The chromophore can be a molecular species attached to the host chain or it can be incorporated in the polymeric structure itself. In general, a good chromophore has an electron donating group connected to an electron... 

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