Second-Order Nonlinear Optical (NLO) Properties of a Multichromophoric System Based on an Ensemble of Four Organic NLO Chromophores Nanoorganized on a Cyclotetrasiloxane Architecture

Abstract

In this paper we report the synthesis, the photophysical, conductometric, and second-order nonlinear optical (NLO) characterization of an ensamble of four NLO active organic tails nanoorganized on a cyclotetrasiloxane ring, to produce various macrocyclic NLO chromophores. The second-order NLO response of the macrocyclic NLO chromophores measured by the EFISH technique as μβ1.91, where μ is the dipole moment and β1.91 the projection along the dipole moment axis of the vectorial component of the quadratic hyperpolarizability working with an incident wavelength of 1.907 μm, increases, compared to the reference monomeric NLO chromophores, from 2.8 up to 3.5 times for nonionic macrocyclic NLO chromophores. The increase is mainly due to an increase of the dipole moment when compared to reference monomeric NLO chromophores while the β1.91 values remain almost unchanged. These macrocyclic NLO chromophores can be also considered as a simple model of a monolayer of organic NLO chromophores on a chemically engineered silica surface. Since the factor controlling their second-order NLO response is the orientation toward the dipole moment axis of the single organic NLO active tails, this kind of model confirms that the second-order NLO response of a monolayer of organic NLO chromophores on a chemically engineered silica surface is controlled by the topology of the binding sites on the surface, as suggested by previous investigations on multilayers on chemically engineered silica surface. The macrocyclic NLO chromophore with a ionic organic NLO active tail shows a strong concentration dependence of its second-order NLO response to be ascribed to a larger increase of its ionic dissociation by dilution, when compared to that of the reference ionic monomeric NLO chromophore. This behavior is evidence of a cooperative effect due to the nanoorganization, to be ascribed to a more facile ionic dissociation of the single ionic organic tail originated by a local increase of the solvent polarity favored by the closeness of the positive charges of the four organic tails. Finally it was shown that the Si(OSiMe3)3 group behaves in a classical organic push−pull NLO chromophore as a pull group as strong as the nitro group.

A Joint Experimental and Theoretical Investigation on Nonlinear Optical (NLO) Properties of a New Class of Push–Pull Spirobifluorene Compounds

“…In this sense, data has been reported in the literature concerning multichromophoric molecular systems such as calixarenes [8][9][10] and cyclotetrasiloxane rings, [11] or multilayered organized systems, where NLO molecules have be assembled by using zirconium phosphate-phosphonate (ZrPO x ) techniques, [12][13][14] layer-by-layer siloxane-based selfassembly, [15] or Langmuir-Blodgett techniques. [16] An interesting way to prepare geometrically oriented push-pull bichromophoric systems is to covalently arrange them into a highly delocalized structure with an orthogonal spatial arrangement, as in the case of 9,9Ј-spirobifluorene, where two fluorenes are connected through an sp 3 -hybridized carbon atom ( Figure 1).…”

The Role of the Chromophore Size and Shape on the SHG Stability of PMMA Films with Embebbed NLO Active Macrocyclic Chromophores Based on a Cyclotetrasiloxane Scaffold

“…19 The much higher stability in the time of the PMMA film containing 2a could be tentatively attributed to the increased size and in particular to the shape of The Journal of Physical Chemistry C ARTICLE the chromophore 2a due to the presence, in the para position of the aromatic ring, of the large Si(OSiMe 3 ) 3 group, which acts as a pull group as strong as the NO 2 group. 8 As we will see later, both effects, size and shape, could be relevant for an increased stability in the time of the SHG.…”

“…In fact, higher μβ 1.91 and β 1.91 values were obtained for 2, if compared to those obtained for 1 and 3. 8 Interestingly, the d 33 value at room temperature of the poled PMMA film containing the macrocyclic chromophore 2 decreases only 14% after the switch off of the electric field, to generate a plateau stable at least for 6 months, while this decrease is of 32% over the same period of time when the film contains the monomeric structurally homologous chromophore 2a. The decrease up to the plateau is still quite low (27 and 20%) for the films containing the macrocyclic chromophores 1 and 3, respectively (Figure 4), while the d 33 values of the PMMA film containing 1a or 3a after 39 and 58 days, respectively, could not be measured because they were too low to allow their quantitative determination.…”

“…Second order NLO chromophores 1-3 and 1a-3a were synthesized as previously reported. 8 Soda-lime glass substrate Menzel Gl€ aser (thickness 1 mm) were purchased by Thermo Scientific and cleaned with water/ acetone before using.…”

Convenient Synthesis of New Si-H and Si-Vinyl Functionalized Stereospecific 8-, 12- and 24-Membered Cyclosiloxanes

“…[1,2] They are used in combination or alone in personal care products, and as carriers, lubricants, and solvents in a variety of commercial applications. Cyclic siloxanes also can be used as a core or frameworks in the synthesis of dendrimers, [3,4] liquid-crystallines, [5,6] multimetallic compounds, [7] organic optoelectronic materials, [8][9][10][11] ligands. [12] Interest to these compounds in the field of organosilicon chemistry is caused by exceptionally wide synthetic possibilities and investigations on the structure and properties of cyclic systems.…”