Synthesis of push-pull chromophores including an N-[4-(4-methoxyphenoxy)butyl]carbazole fragment

Abstract

Organic substances with nonlinear optical properties of the second order are the promising materials for molecular electronics and photonics, that is, finally, for telecommunication and electro optical devices [1–6]. These materials possess some advantages if compared with their inorganic analogs: they have high values of nonresonance susceptibility, high nonlinear optic response, high transmissibility, low dielectric permittivity, besides they are sufficiently easy to process and economic [1, 7]. However certain drawbacks in their practical application also exist, e.g., the strong intermolecular electrostatic interaction, poor solubility in common organic solvents, thermal and photochemical instability. By altering the chemical structure of material, namely, by selecting the optimum electron-donor and electron-acceptor substituents it is possible to obtain the maximum nonlinearity on the molecular level and also affect the chemical, photochemical, and thermal stability. The introduction of electron-donor orthoor para-alkoxyphenyl groups into the monomers is known to change the optical properties of chromophores. It results in increasing of the electro optic coefficient value (r33) and molecular hyperpolarizability β [8–10]. When such a group is situated in the peripheral part of a long aliphatic chain and is incorporated into the chromophore structure both intermolecular and intramolecular interaction may occur between the donor and acceptor parts of the chromophore. Besides, the introduction of long-chain substituents in the structure of compounds affects the character of their packing in the solid state and their thermal stability [11]. In this work we continued to study carbazolecontaining compounds including in their structure ω(4-methoxyphenyl)alkyl substituents at the nitrogen atom of this heterocycle [12, 13] and have synthesized two new chromophores 8 and 9 including N-[4-(4methoxyphenoxy)butyl]carbazole moiety as a donor fragment. The optical and electrochemical properties of all prepared during thes work compounds were examined. First from the corresponding α,ωdibromoalkane and p-methoxyphenol 1 in acetone the starting bromides 2 and 3 were prepared [12]. The subsequent alkylation of carbazole with the synthesized bromides under the conditions of the phasetransfer catalysis in the system acetone–16 M water solution of NaОН–benzyltriethylammonium chloride led to the formation of the corresponding N-substituted carbazoles 4 and 5 [13]. The acetylation of the latter at room temperature in dichloroethane in the presence of SnCl4 afforded 3-acetylcarbazoles 6 and 7.