Surface pressure driven supramolecular architectures from mixed H-aggregates of dye-capped azobenzene derivative

We demonstrate a soft chemical approach for the synthesis of dimensionally dictated functionalized mesostructures by continuous tuning of the surface molecular density of a photoreceptable molecule (E)-1-(3-chloro-4-(octyloxy)phenyl)-2-phenyldiazene (compound 1) with Rhodamine B (Rh B). Highly oriented cylindrical microtubules with a hollow center running the entire distance of the assembly in a parallel-packed configuration were formed at the air-water interface. The surface tension driven self-organized structures were evidenced from electronic absorption and steady-state fluorescence spectroscopy in conjunction with optical, polarizing, and epifluorescence microscopy and microspectroscopy; the structural building blocks were identified to be mixed H-aggregates from compound 1 and Rh B of 1:1 stoichiometry, corroborated by a blue shift in the characteristic absorption features. The appearance of a crossover point (apparent isosbestic point) instead of a sharp defined isosbestic point in the absorption spectra signified the formation of mixed H-aggregates from trans-azobenzenes in ion-dipole interaction with the charged Rh B. Increasing the temperature induced an end-to-end self-assembly of the hollow tubules, and photoisomerization of compound 1 did not serve as a trigger to induce self-organization. A nonfluorescent planar crystalline morphology with irregular topology was observed for its isomer (E)-1-(4-chlorophenyl)-2-(4-(octyloxy)phenyl) diazene (compound 2).