989. Physical properties and chemical constitution. Part XLIII. The electric dipole moments of azobenzene, azopyridines, and azoquinolines

Abstract

The electric dipole moments of cis-and trans-azobenzene, two cis-and three trans-azopyridines, and of five azoquinolines have been calculated from measurements of the dielectric constants, specific volumes, and refractive indices of their solutions in pure benzene a t 25.00'. Of the azoquinolines, only the 6,6'-isomer showed any change in its dipole moment after exposure to ultraviolet light. The conformations of the various molecules in solution are discussed.THE electric dipole moments of azobenzene and of the azopyridines have been measured previously. That reported for 4,4'-azopyridine (2.0 D) seems exceptionally high, and merits further investigation, but in any case the results have only been employed in discussing cis-trans isomerism. Equally interesting are the conformations of these molecules, as it is unlikely that either the cis-or the trans-forms are planar in solution. The dipole moments of five azoquinolines have also been measured. Only with the 6,6'isomer did irradiation with ultraviolet (u.v.) light change the dipole moment, indicating a very small conversion of the stable trans-into the less stable cis-form. The U.V. spectra of the compounds in pure ethanol were measured and agreed with published results.3 EXPERIMENTAL AND RESULTSPreparation and Purification of the Azo-compounds.-The dipole moment of each compound Azobenzene. Purified nitrobenzene in methanol was reduced by refluxing with sodiumThe mixture was neutralised, filtered, most of the It was then filtered off, washed The into the cis-isomer by irradiation in glacial acetic acid A Hanovia mercury vapour lamp, placed 25 cm. from the Most of the residual trans-isomer was precipitated with water and filtered The remaining azobenzene was extracted with cold chloroform, washed rapidly with was measured immediately it had been purified.hydroxide and powdered zinc for 12 hr. methanol distilled off, and the compound allowed to crystallise. well with water, and warmed with dilute hydrochloric acid to remove occluded zinc salts. trans-azobenzene was washed, dried, and recrystallised from ethanol to constant m. p. (69"). solution with U.V. light for 6 hr. solution, was used. off. trans-Azobenzene was converted

Synthesis and Surface-Active Properties of New Photosensitive Surfactants Containing the Azobenzene Group

“…The distance between two para carbons of each aromatic ring is 5.5Å for the cis isomer and 9.0Å for the trans one. The dipole moment and molecular phase of the cis isomer are also quite different from those of the trans one (19,20).…”

Features of Photomechanical Response in Monolayers Composed of a Charged Amphiphilic Azobenzene Polymer

“…11 The film deformation mechanism is considered as follows. The trans to cis photoisomerization caused by UV illumination leads to dipole moment increase from 0.5 to 3.1 D. 13 The polarity increase in the trans to cis isomerization process gains attraction with the water surface, and consequently the film area expands. The reverse process occurs upon visible light illumination, leading to film contraction.…”

A Thermally Adjustable Multicolor Photochromic Hydrogel

“…Azobenzene derivatives included in polymers can form the basis of a light-triggered molecular switch that induces conformational changes in the polymer, variations in viscosity and solubility, and changes in the mechanical strength of the polymer. [12][13][14][15][16] In this study, a reversible change in the dipole moment of the azobenzene moiety [17] was used to induce a volume change in the gel. Azobenzene is almost entirely in the trans configuration; it has no dipole moment at room temperature in the dark.…”