Encapsulation of Stimuli-Responsive Molecules for the Preparation of Photofunctional Materials

Nuria Alejandra Vázquez Mera

Dr. Daniel Ruiz Molina Dr. Jordi Hernando Campos Dr. José Luis Bourdelande Fernández

Colour plays an important role in our everyday life and not only from an aesthetic point of view. There is a big market centred in technological applications derived from chromic phenomena and colour science, encompassing from the classical commercial uses of dyes and pigments to visual displays, light emitting diodes, optical data storage and optoelectronics, among others. Particularly, the smart materials community has paid special attention to systems exhibiting a reversible colour change upon application of external stimuli - namely, chromism. In this thesis we have been specifically interested in photochromic and thermochromic organic dyes whose colour-tuneability is induced by light irradiation and temperature variations, respectively. These compounds present a wide range of potential applications; however, their usage is not straightforward since in many cases the well-established chromic properties of these species in solution are modified or inhibited when applied in solid materials. The aim of this thesis is to propose and explore a novel methodology to address this issue and allow the direct transfer of photo- and thermochromic properties from solution to the solid state. Basically, it consists in the encapsulation of the photo- and thermochromic compounds of interest inside liquid-filled polymeric capsules, which should preserve their solution-like chromic behaviour and offer the possibility to introduce these systems into any type of matrix that would restrain their colour tuneability when directly incorporated. As proof of concepts of this strategy, three specific types of photoactive systems have been developed along this thesis: (i) fast-responsive photochromic coatings for photoprotective purposes (ii) solid thermochromic materials made of valence tautomers (iii) white-light colour-tuneable materials based on thermoresponsive fluorophores.

The thesis explores innovative applications of photo- and thermochromic dyes through their encapsulation in liquid-filled polymeric capsules, allowing solution-like chromic behavior to be transferred to solid-state materials. Applications include fast photochromic coatings for ophthalmic lenses and smart surfaces, thermochromic systems for molecular memory and sensors, and color-tunable white-light emitters for lighting and display technologies. The method overcomes major limitations in chromic material integration and has led to patented technologies, industrial interest, and expansion into new applications such as temperature-responsive inks and fragrance capsules.

Colour; Chromic Phenomena; Colour Science; Technological Applications; Dyes; Pigments; Visual Displays; Light Emitting Diodes; Optical Data Storage; Optoelectronics; Smart Materials; Reversible Colour Change; External Stimuli; Chromism; Photochromic Organic Dyes; Thermochromic Organic Dyes; Light Irradiation; Temperature Variations; Colour-Tuneability; Potential Applications; Solid Materials; Novel Methodology; Direct Transfer; Photochromic Properties; Thermochromic Properties; Solution to Solid State; Encapsulation; Liquid-Filled Polymeric Capsules; Solution-like Chromic Behaviour; Matrix; Colour Tuneability; Photoactive Systems; Fast-Responsive Photochromic Coatings; Photoprotective Purposes; Solid Thermochromic Materials; Valence Tautomers; White-Light Colour-Tuneable Materials; Thermoresponsive Fluorophores