Viologen capped by nucleobase—building blocks for functional materials: synthesis and structure–properties relationship

The current study presents a new class of functional derivatives (1–3) consisting of a dicationic viologen (4,4’-bipyridinium unit) (V2+) capped by nucleobases thymine (NB1), adenine (NB2), thymine/adenine (NB1, NB2), and ion-paired with amphiphilic anion 3,4,5-tris(dodecyloxy)benzene sulfonate (DOBS−). The target of our work focuses on the design and synthesis of molecular building blocks in which three different functionalities are combined: chromophore (V2+ unit), molecular recognition (NB unit), and thermotropic liquid crystal (DOBS unit). The resulted materials exhibit liquid crystalline properties at ambient temperature with significant particularities-induced by nucleobases in the mesogen structure. Structure–properties relationship study focuses on providing knowledge about (1) how the thermotropic, redox properties, thermochromism, or ionic conductive properties are influenced by the presence of purinic or pyrimidinic nucleobases, and (2) how effective is their ability to self-assembly by hydrogen bonding in nonpolar solvents. The presence of nucleobases has been proved to have a substantial impact on electron transfer rate during the reduction of viologen moieties by intermolecular aggregation. Ionic conductivity and thermochromic properties of derivatives 1–3 were investigated and compared to a non-containing nucleobase analog methyl viologen with 3,4,5-tris(dodecyloxy)benzene sulfonate anion (MV) as reference. Graphical abstract

Acid Solution Processed VO2-Based Composite Films with Enhanced Thermochromic Properties for Smart Windows

As a typical thermochromic material, VO2 coatings can be applied to smart windows by modulating the transmission of near infrared (NIR) light via phase transition. However, the inherent undesirable luminous transmittance (Tlum) and solar modulation efficiency (ΔTsol) of pure VO2 impede its practical application. In order to solve this problem, the porous VO2 based composite film was prepared by magnetron sputtering and subsequent acid solution process with Zn2V2O7 particles used as a sacrificial template to create pores, which showed excellent Tlum (72.1%) and enhanced ΔTsol (10.7%) compared with pure VO2 film. It was demonstrated that the porous structure of the film caused by acid solution process could improve the Tlum obviously and the isolated VO2 nanoparticles presented strong localized surface plasmon resonance (LSPR) effects to enhance the ΔTsol. Therefore, this method will provide a facile way to prepare VO2 based films with excellent thermochromic performance and thus promote the application of the VO2 based films in smart windows.

Poplar-based thermochromic composites that change colour at 38 °C to 46 °C

The red thermochromic dye (R-TD) is the tetradecanoic acid tetradecyl ester (C28H56O2) and methyl red (C15H15N3O2) mixture that has better permeability enabling its infiltration into wood and better thermochromic properties changing its colour at above 30 °C after about 0.5 min. Thicker poplar-based thermochromic composite specimens (R-PTC, thickness: 5.0 mm) were prepared by filling the R-TD into pre-treated poplar veneer (thickness: 5.0 mm) thus allowing better penetration after pre-treatment. After R-TD infiltration, the R-PTC samples were covered by polypropylene wax for preventing R-TD from overflowing from R-PTC under the action of phase-change temperature. This R-PTC, whose colour can change from light-red to dark-red at 38 °C to 46 °C, can recover to light-red at below 38 °C after about 14 h, and the peak of colour change is at about 42 °C. R-PTC will be suitable for materials used in thermochromic furniture that can indicate the surface temperature to potential users, thus allowing assessment of likely scalded pain when used the furniture.