Self-Organized Ureido Substituted Diacetylenic Organogel. Photopolymerization of One-Dimensional Supramolecular Assemblies to Give Conjugated Nanofibers

Abstract

The introduction of the urea function as structure directing agent of diacetylene organogels (DA-OGs) has been achieved. Despite the urea function being one of the most frequently used structure directing agents for the formation of organogels, it has never been exploited in the fabrication and photopolymerization of DA-OGs. The self-association of ureas involving two hydrogen bonds is much stronger than that of urethanes or amides, and the resulting supramolecular assemblies are completely insoluble. In this context, 1,1'-(hexa-2,4-diyne-1,6-diyl)bis(3-(10-(triethoxysilyl)decyl)urea) 2 was synthesized. Compound 2 was soluble owing to the triethoxysilane function that we recently used in the fabrication of a silylated bis-urea-stilbene organogel. It formed an organogel, and its photopolymerization was studied in cyclohexane. The loss of the gel state and the formation of a red solution resulting from the polymerization were found to be the result of the constraints introduced by the urea function in close vicinity to the polymerizable function. To obtain an ureido substituted diacetylenic organogelator affording a blue highly conjugated polydiacetylene (PDA) without a sol-gel transition, a propylene spacer was introduced to move the urea function away from the polymerizable function (derivative 3). The thermochromism exhibited by the latter in the solid state was studied. Using the same setup and the same sample, UV-vis and FTIR spectra were simultaneously recorded as a function of the temperature to highlight a relation between color changes and urea association mode changes. The data showed that the reversible thermochromic transition must be associated with a reversible supramolecular modification and, conversely, that irreversible chromic transitions are the result of irreversible structural modifications. The chromic effects of the acidic hydrolysis-polycondensation of the trialkoxysilyl groups to form a siloxane network were studied on a thin film of 3. In the same way, solvent effects on the color of the organogels of 3 were also investigated. Correlations could be established between the different stimuli. These results provide a deeper understanding of the precise molecular mechanism of the blue to red transition and of the reversibility of the purple to red transition generally encountered in PDA thermochromism.

Gels with sense: supramolecular materials that respond to heat, light and sound

“…In a study by Weiss et al, a chiral amide-containing poly(diacetylene) was found to form blue left-handed quadruple helices in solution, which convert to red righthanded double helices and yellow isolated fibrils upon the addition of trifluoroacetic acid. 295 Similarly, Dautel et al reported that a polymer derived from a urea-functionalised butadiyne forms a blue gel in cyclohexane but converts to a red gel when heated to 130 o C, with a purple intermediate observed at 40 o C. 296 Whilst the blue-to-purple transition is irreversible and associated with a thermodynamic relaxation of the hydrogen bonded network, the purple-to-red transition is reversible until the temperature reaches 120 o C, whereupon the molecules adopt a non-hydrogen-bonded packing arrangement. Effects of this nature arise due to changes in the spacing and relative orientations of π systems and are thus strongly influenced by molecular geometry.…”

Ultrafast and reversible thermochromism of a conjugated polymer material based on the assembly of peptide amphiphiles

“…2,3 The chromatic transition of PDA can be directly detected by the naked eye, enabling a broad spectrum of optoelectronic and sensing applications. [4][5][6][7][8][9] However, the available PDA materials oen suffer from a slow response time (tens of seconds to minutes), low reversibility (tens of cycles or even irreversible), a narrow working temperature range (less than 90 C without the introduction of inorganic components) and poor mechanical properties, mainly due to the relatively low structural regularity and strength of molecular interactions. Based on the same reasons, the available chromatic polymers have generally been made into powders or lms, and it remains challenging to achieve continuous bres that are required for wearable electronics, which are a promising direction in sensing applications.…”

Ultrasound Switch and Thermal Self‐Repair of Morphology and Surface Wettability in a Cholesterol‐Based Self‐Assembly System

“…Despite a wide range of reported responsive materials, the mostly used stimuli involve light, [5] reaction, [2] and heat. [6] However, it should be noted that development of a smart or adaptive gel which can be controlled or even switched by sound [7] and thixotropy [8] is also very appealing.…”