Chromogenic and fluorogenic materials based on micro and nanocapsules

Resumen

During the last years smart materials community has paid special attention to systems exhibiting color and emission changes upon application of a certain stimulus (chromogenic). However, though there are a large variety of chromogenic/emissive examples in solutions producing complex effects, their integration into solid materials, relevant for real applications, always generates problems of reproducibility, tunability and modification or inhibition of the optical performances. The aim of this thesis is to develop a straightforward and universal strategy that not only allows obtaining stimuli-responsive (light, temperature, pH) solid materials but gives also access to: i) direct transfer of bulk solution chromogenic/emissive properties (even combination of them) into the solid state, ii) easy tunability of the optical performances and iii) sophisticated chromogenic effects, beyond the typical photochromic and thermochromic response. Remarkably the tunability is easily achieved by using readily available components, without modifying the chemical structure of the active species. The general strategy relies on the assembling of chromogenic and emissive dyes with interacting media/molecules in micro/nanostructures obtaining performances that could not achieve otherwise. In all developed materials in this thesis the micro/nanostructures are based on: i) organic dyes (photochromic, thermochromic, fluorescent), ii) organic non-volatile media or phase change materials (which can be liquid or solid at RT) and, when needed other additives (e.g. color developer) that selectively interact (via complex formation, H-bonding or acid-base reaction) with the contained dye inducing specific optical properties in one of the two phases and, iii) structuration as polymeric capsules (core-shell or matrix type). Playing with the design of the arquitecture of these structures, highly tunable chromogenic micro/nanostructures that respond to different (multi)stimuli changing the color and/or the emission properties are obtained, in the solid state. As a proof of concept of this strategy three types of advanced chromogenic materials have been developed: i) polymeric films with tunable and switchable reverse photochromism, ii) multiresponsive (pH and temperature) materials, and iii) high-temperature threshold fluorescent sensors