(18в€’20) In some cases, the percentage of energy savings reached to more than 16%. In this context, thermochromic substances, embedded in coatings, are beginning to surface in the design of new materials for energy saving.

In the solid matrix, a hysteresis effect of color transition may be affected by the nature of the matrix. Widely used matrices include waxes and polymers which are compatible with the thermochromic substance. (17) The thermochromic transition temperature of a pure substance may be greatly changed by dispersing the compound in a solid matrix or by mixing it with other substances. (15,16) A fewer known examples are as a result of equilibria between complexes in solution or to equilibria between different molecular structures in the case of organometallic compounds. For inorganic compounds, this transition is frequently due to a change in the crystalline phase, to a change in ligand geometry, as a result of charge transfer, (13) modifications in the chemical structure, (14) or to a change in the number of molecules of the solvent in the first coordination sphere. (10в€’12) The thermochromic color change of a compound/material is distinguished often by eye, occurring over a small or sharp temperature interval. Thermochromism, defined as reversible change in the color of a compound when it is heated or cooled, has received little attention as an energy harvesting mechanism. (2в€’4) In this context, photochromic systems where a molecule is converted by photoisomerization into a higher-energy isomer, which is capable of storing the energy until released by a trigger, converting the metastable isomer to the original light-harvesting isomer, (5в€’9) have played a significant role. The schemes generally known as molecular solar thermal systems, for example, phase-changing materials that store energy in the form of lattice energy, represent a promising avenue for harvesting and storing solar energy. In relation to this, it is a major challenge to store energy due to daily and seasonal variations in the accessibility of sunlight. Solar energy is a viable and inexhaustible source of energy (1) for generating power, with the aid of solar cells, and harnessing its heat via efficient storage of sunвЂ™s heat using compounds/materials with high heat capacities.

These aspects have led to an increasing focus on the short-term stored energy resources, which could be derived from wind power, hydropower, solar power, biomass, and so forth. Global energy demand has focused attention on sustainable energy generation coupled with optimized use of energy and minimized pollution, limiting fossil fuel-based energy consumption to a bare minimum. The ever-increasing global energy demands, due to expanding developments and increasing populations, have led to serious scrutiny over the depleting energy resources.

Interestingly, when embedded in a polymeric matrix, thin films with high recyclability and long life are also described. Most of the investigated systems show a chromogenic transition from pink to blue, occurring in a temperature range suitable for practical applications (40вЂ“60 вЊ). The thermochromic systems were analyzed both as solutions and as thin films, and the data collected highlight the defining role played by both the cation structure and the solvent nature in determining their performance. The analysis of the above factors was carried out through a combined approach of different techniques, that is, variable temperature UVвЂ“vis and NMR spectroscopies, conductivity, and thermal gravimetric analysis. Different structural changes on the cation, the nature of the anion, and the nature of the IL used as the solvent were considered. With the aim of obtaining thermochromic systems with potential applications in solar energy storage, we evaluated the behavior of some sugar-based ionic liquids (ILs)вЂ“Co(NTf 2) 2 complexes, in IL solution, as a function of temperature.

Key ionic activation bypass