A practical spectroscopic and theoretical approach to study the electrochromism in molecular-based materials: The case of a family of dendrimerlike poly(6-azulenylethenyl)benzenes

A series of branched poly(6-azulenylethenyl)benzene derivatives consisting of a central benzene ring surrounded by acetylene-bridged 1,3-bis(n-hexyloxycarbonyl) azulene arms has been investigated by physical and theoretical methods. Their optical and electrochemical features have been explained with the help of calculations regarding their 7 nature and extension of the lowest unoccupied molecular orbitals (LUMOs), the key factors that modulate their properties. The highest occupied molecular orbitals are located at the periphery of the molecules whereas their LUMOs also extend into the central core by which these molecules can be regarded as antennae systems. With an increase in the branching, the electronic structure of these molecules seems to be mostly affected at the level of the central phenyl core plus the acetylene bridges. The combination of Raman spectroscopy and calculations gives the possibility of analyzing particular geometrical and structural parameters otherwise hardly accessible by other techniques. Reduced species are characterized by double bond cumulated structures within the acetylenic spacers that give rise to a planarization of the molecules upon negative charging. Extensive intermolecular interactions, otherwise explaining their liquid crystalline behavior, both in solid state and in solution have been observed.