Development of wavelength selective shutters for device application for filters and smart windows

Ideal wavelength selective shutters (or filters) need to have sharp, high intensity, easily switchable absorption bands in the desired region of the electromagnetic spectrum. If such devices are to be used for smart window applications, then selective control of all the visible and near infra-red regions of the electromagnetic spectrum would be desirable. No single material, as yet, offers such selectivity. The choice and properties of such material would also depend on ease of use and friendliness to the environment. Metal phthalocyanine materials are potentially useful electrochromics, the neutral molecules are nontoxic, brightly coloured (have narrow absorption bands with high extinction coefficients) and are also stable to heat and light. Metal bisphthalocyanine electrochromics (where the metal is based on the rare earth elements, Zr, Sn or Pb) have some promise in this area and are discussed. A number of metal monophthalocyanines, compounds where the metals are transition elements (such as V, Cr, Mn, Fe and Co) and nontransition elements (such as Al, Si and Sn) that offer some useful spectral properties, are also discussed. The possibilities of using `cocktails´ of these compounds to give desirable performance, their projected advantages and disadvantages are also debated. A bright future is envisaged for these materials