Polymeric and monomeric azo-based materials have opened up a new route toward holographic data storage through the discovery of bulk photoassisted molecular migration, which can create complex microstructured surfaces.[1] Most of the studies reported so far have involved highly azofunctionalized matrices where surface relief gratings (SRG) are detected by using atomic force microscopy (AFM) [2] or Raman microspectroscopy.[2]However, such an approach faces intertwined parameters (chromophore dipole-dipole interactions, length and stiffness of the polymer chain and linker, etc.) that make the rational design of optimal systems rather delicate. In contrast, azo-doped matrices allow simpler phenomenological descriptions but they suffer weak surface modulation and poorly contrasted AFM imaging. Surprisingly, no use of emissive azo-based molecules has been reported, and yet fluorescence detection offers one of the most sensitive techniques for detecting microscopic events such as molecular migration. We report herein the synthesis of highly fluorescent azo derivatives whose dynamic fluorescence and photoisomerization properties were thoroughly studied before investigating the formation of gratings by using fluorescence confocal microscopy.The targeted azo derivatives were fabricated from fluorescent squaryl groups covalently linked to a photoisomerizable Disperse Red 1 (DR1)-type azo moiety by an ethyl unit (Scheme 1). DR1 is regarded as the photochromic archetype in SRG studies and can be easily excited by use of an Ar + laser.[3] Squaraine derivatives, known for their photoconducting, nonlinear-optical, and chemical-sensing properties, [4,5] emit in the red with high fluorescence quantum yields. This favors little emission quenching through the inner filter effect and/or Förster exchange with the azo unit. The azo part 3 was synthesized first after a two-step procedure to reduce the risks of nucleophilic attacks on the squaraine carbonyl centers (Scheme 1). Tosylation of DR1 in the presence of p-toluenesulfonyl chloride (tosylate chloride) and triethylamine (Et 3 N) at 0°C in dichloromethane produced 2 with a 85 % yield. Subsequent nucleophilic substitution of 2 by N-methylaniline in dimethylformamide at 100°C for 6 h produced 3 with a 25 % yield. Compound 3 was finally coupled to the dialkylsquarates 4a-b [6] in refluxing propan-2-ol, with orthobutylformate as an in situ drying agent. [7] After purification, the bifunctional compounds 5a and 5b were obtained as dark-green powders (yield 20-25 %). At this point, the choice of N-butyl over N-methyl substituents for 4 was crucial to ensure good solubility, and full 1 H and 13 C NMR characterizations. The UV-vis absorption spectra of 5a and 5b in chloroform solution showed two main bands centered at 473/632 nm and 473/638 nm, respectively (Table 1). These latter have been assigned to the azo-and squaraine-based p-p* electronic transitions, respectively, through comparison with the absorption spectra of the constitutive model units 3, and the symmetric bis [4-(dimethyla...
This work was aimed to produce elongated nanoparticles of clinical interest by the stretching method. Polymer films prepared from material recovered from the dissolution of a marketed stretchable water-soluble film were loaded with 10% of poly(isobutylcyanoacrylate) nanoparticles. The films were elongated at 50°C to 230% of their initial lengths. The shape factor of the nanoparticles recovered after elongation was consistent with stretching conditions applied on the film. This work has demonstrated the feasibility of the preparation of non-spherical poly(isobutylcyanoacrylate) nanoparticles by the stretching method and described conditions to apply the method.
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