The combination of photoinduced molecular switches and polymers can give rise to a variety of smart photofunctional materials with application in different fields. This was the main goal of this thesis, which was pursued using two different approaches a) the functionalization of polymer matrices with spiropyran switches, with which we aimed to develop novel photoresponsive materials for CO2 capture and sensing; and b) the use of diarylethene photoswitches as crosslinkers for the photoinduced preparation of polymer networks with enhanced light-control. In the first part of the thesis, we demonstrated that light-controlled colorimetric detection of gaseous CO2 with solid materials could be accomplished by combining the acido- and photochromic behavior of spiropyrans with the internal structure and composition of hydrogels. To do so, we first proved that chemically tailoring the acid-base properties of water-soluble SP allows discriminating their acidochromic response when exposed to gases of different acidity - e. g. , CO2 and HCl. To transfer this behavior to the solid state, we prepared hydrogels functionalized with SP of distinct acid-base properties, whose pKa values were proven to be essentially preserved inside these materials. As a result, differential colorimetric responses could be promoted for these hydrogels when treated with CO2 relative to HCl, thus allowing selective optical detection of carbon dioxide. In addition, we demonstrated that the CO2-induced color changes in the hydrogels are fast, quantifiable and reversible upon CO2 desorption, while they can be directly measured at the gas-solid interface without the need of immersion or pretreatment with water. Additionally, we proved that violet light irradiation promotes CO2 desorption, thus obtaining a light-induced recycling of the sensing material. In the second part of this thesis we explored three types of photoligation reactions that could be applied to the preparation of polymer networks under two-color control using photoswitchable diarylethene-based crosslinkers: i) oxo-Diels-Alder reactions, ii) amidation, and iii) hemiketalization. In the case of the oxo-Diels-Alder reaction, we prepared a methacrylate copolymer decorated with the photoactivable diene precursor and a difunctional photoswitchable dienophile presenting two DTE-COCF3 units, which were used to optimize the reaction conditions to regulate polymer crosslinking under two-color irradiation - i. e. , it was efficiently induced at λexc = 365 nm and could be halted upon concomitant illumination at λexc = 625 nm. This antagonistic methodology was proven to enable two-color control of solid polymer network generation and, by shaping the red illumination beam with a mask, spatially-patterned polymer thin films were successfully generated. To explore the two-color control of amide bond formation, a novel strategy was devised based on the preparation of esters of photochromic DAE cores made of a phenol and a thiophene ring. In their open isomer these compounds present a phenolate group that should be a poor leaving group for the reaction with amines; in contrast, they transformed to enol esters upon photoisomerization to the closed state, which should produce a much better enolate leaving group for amidation due to keto-enol tautomerism. However, preliminary tests of reactivity of those DAE-esters with an amine showed no modulation of the reactivity upon photoisomerization, which prevented their use for the preparation of polymeric materials. The final strategy that was explored in this thesis for the two-color control of polymer network formation was the hemiketalization process between hydroxyl groups and photoswitchable carbonyl dienophiles. To test this concept, we studied the reaction between ethanol and trifluoromethyl ketone groups attached to a DAE core, whose electrophilicity should change upon photoisomerization. In particular, a 50-fold enhancement in reactivity was achieved in DMSO for the first hemiketalization reaction of ethanol with the closed DAE state.
Light-responsive polymer systems based on molecular photoswitches
Marco Ariza, A. (Author). 26 Nov 2024
Student thesis: Doctoral thesis
Student thesis: Doctoral thesis