One of the perspective ways of realization of molecular switching is exploitation of redox-isomerism, which is a reversible and controlled intramolecular electron transfer that results in changes of physico-chemical properties and the molecular size. The latter can be utilized in the development of a so-called molecular muscle, where spatial changes lead to overall lengthening/shortening of the assembly of redox-isomeric molecules. Phthalocyanine derivative complexes are considered as one of the most promising compounds for these applications due to their ease of modification and ability to form complexes with a wide series of metals. We propose investigation of Langmuir monolayers of a series of bis-tetra-crown-phthalocyaninates of several lanthanides. Combined studies by in situ UV-vis spectroscopy, GID and XANES will allow us to determine the exact conditions of redox-isomeric transformations and accompanying spatial changes of the studied molecules.