Chromogenic & Emissive Nanomaterials for Energy Efficient Devices

In this research line we aim to develop advanced nanostructured molecular materials that smartly modify their optical properties (i.e. absorption and emission) as response to external stimuli, such as pH, temperature and light. These materials are of key relevance in near future commercial products that try to tackle society and environmental needs: sustainability, comfort and security.

  • UV/vis/NIR-light induced color-changing films and coatings for rewritable devices, anticounterfeiting technologies and dynamic photoprotective coatings.
  • Temperature-responsive fluorochromogenic micro/nanocomposites for thermal optical sensing and temperature-dependent optical filters.
  • Vis/NIR activated upconverting fluorescent materials for energy conversion, anticounterfeiting technologies and (bio)imaging.

For this we follow novel and emerging concepts, principally based on the micro/nanoencapsulation of oil or phase change materials mixtures of molecular dyes (such as spirooxazines, spiropyrans, porphyrins and polycyclic aromatic hydrocarbons), which allow advanced, tunable and customizable optical change effects of different degrees of sophistication: from highly fast to irreversible responses, multiresponsiveness, multiple output (color, fluorescence), threshold-based changes, invisible (to the human eye) optical variations.

Sustainability

The energy demand in the modern society is increasing exponentially. A large part of this (30-40%) is requested to run heating and cooling systems in buildings. In line with the European Green Deal and with the aim of contributing in zero-energy buildings, we develop novel chromogenic materials that respond to variation of solar light (UV, visible, NIR radiation) and environmental temperature. We develop molecular-based nanocomposites (coatings, laminates) that could be integrated in glasses and plastic materials for the new generation of smart windows and greenhouses that self-adapt to the external conditions, filtering, capturing, storing and converting the energy coming with the incident light. These materials are based on encapsulated photochromic dyes, NIR-absorbing thermochromic pigments, NIR-responsive plasmonic nanoparticles, and nanostructured liquid crystals.

Confort and Safety

The glare produced by the sunlight or car intense headlights is a source of disturb and danger during driving, riding or sports activities. Though standard sunglasses help in some circumstances performing these activities with better comfort and safety, they provide too much darkness when passing to a less illuminated area, e.g. inside a building, tunnels or roads in the shadow. Photochromic materials compensate the different glaring states by self-tinting depending on the light intensity conditions. However, standard photochromic materials, used in ophthalmic lenses, suffer the slow tinted/clear transition passing from an illuminated to a dark condition. In this respect, we aim to develop highly transparent photochromic films that show very fast response: they quickly develop a tint upon exposure to sunlight and recover within seconds the clear state in the dark. With the company Futurechromes S.L., we are currently focused on preparing marketable prototypes of ophthalmic glasses, helmet face shields, mirrors and self-tinting windows, based on nanocapsules technology. In the future, the applicability of these materials could be expanded to greenhouses and electronic devices (touch screen, camera lenses, etc.). 

Devices and Security

Our approach is highly modulable and allows obtaining fluorochromogenic materials of different degree of complexity that could be integrated into different devices. Temperature-, pH- and chemical sensitive organogels, films, suspensions and cellulose papers have potential use as optical sensors. So far we have generated a broad variety of thermoresponsive sensors: chromogenic vs fluorogenic, reversible vs irreversible, detecting from very low (-270 oC) to very high (100 – 200 oC) temperatures.

To face expert and technologically competent counterfeiters, the security inks industry must design and fabricate constantly novel anticounterfeiting marks, made of materials of enhanced complexity, which are difficult to reveal and reproduce and which mechanism of detection could not be easily unfolded. Our specialty micro/nanomaterials undergo threshold or NIR-activated optical changes, behave as invisible inks (NIR/UV-absorbing or fluorescent), or respond to multiple stimuli (e.g. light + temperature or pH + temperature). These features add a superior degree of sophistication, which make them highly attractive for anticounterfeiting technologies. The developed materials, obtained as suspensions, powders or films, could be applied and printed in banknotes, identification or other relevant documents, pharmaceutical products, etc.

Our chromogenic films allow the straightforward fabrication of solid-state devices using commercially available organic molecular dyes. Our encapsulation strategy overcomes the recurrent problem associated to these dyes that lose their high performing properties once integrated in the solid device. We thus achieve low-energy (visible/NIR) activated rewritable boards and white-light emitting films, which emission can be easily controlled with temperature.