Effect of chromophore–chromophore electrostatic interactions in the NLO response of functionalized organic–inorganic sol–gel materials

Abstract

In the last years, important non-linear optical results on sol-gel and polymeric materials have been reported, with values comparable to those found in crystals. These new materials contain push-pull chromophores either incorporated as guest in a high T g polymeric matrix (doped polymers) or grafted onto the polymeric matrix. These systems present several advantages; however they require significant improvement at the molecular level -by designing optimized chromophores with very large molecular figure of merit, specific to each application targeted. Besides, it was recently stated in polymers that the chromophore-chromophore electrostatic interactions, which are dependent of chromophore concentration, have a strong effect into their non-linear optical properties. This has not been explored at all in sol-gel systems. In this work, the sol-gel route was used to prepare hybrid organic-inorganic thin films with different NLO chromophores grafted into the skeleton matrix. Combining a molecular engineering strategy for getting a larger molecular figure of merit and by controlling the intermolecular dipole-dipole interactions through both: the tuning of the push-pull chromophore concentration and the control of TEOS (Tetraethoxysilane) concentration, we have obtained a r 33 coefficient around 15 pm/V at 633 nm for the classical DR1 azo-chromophore and a r 33 around 50 pm/V at 831 nm for a new optimized chromophore structure. +: Work supported by DGAPA UNAM IN 103199, and CONACYT 34582-E. Reyes-Esqueda et al. "Effect of chromophore-chromophore electrostatic interactions in the NLO response of functionalized organic-inorganic sol-gel materials".

Optical Properties of Functional Hybrid Organic–Inorganic Nanocomposites

“…By molecular engineering towards large electrooptic molecular figures of merit (using a simple two-state twolevel model) and suitable thermal stability, and by controlling the intermolecular dipole±dipole interactions by tuning push± pull chromophore concentration, Blanchard-Desce et al [146] have recently shown the ability to prepare hybrid thin-films with very large electro-optic coefficients. For instance, using push±pull phenylpolyene chromophores grafted to the silica matrix with a lb eight times larger than that of DR1 and carbazole units to avoid dipolar chromophore interactions, this strategy has led to a very high electro-optic coefficient (r 33 ) of 48 pm V ±1 at 831 nm, [147] which is suitable for electro-optic applications. In summary, better results are generally obtained when NLO dyes are grafted to the oxide matrix via several covalent bonds (hybrids of class II).…”

Versatile Synthesis of Soluble Multifunctional Thiophene Copolymers with NLO Activity

“…This shift slightly increases with chromophore concentration (i.e., 14 nm for P2 and 8 nm for P2*), a behaviour that may be ascribed to dipoledipole interactions leading to a multimeric association of chromophores. [15] More significantly, a decrease of absorbance is observable in the spectra of both copolymers after poling. Different mechanisms may account for this behaviour:…”

Chromophore aggregation and photoinduced dichroism in sol–gel films

“…The superposition of the two bands appears as a blue-shift of the absorption band. During photoisomerization, the aggregates can be broken [12], trans molecules are freed, the number of molecules with the absorption maximum near the wavelength of the probe increases and this gives additional contribution to T 0 [6,13].…”