Systematic investigation of the structure-properties relationship of the DHA/VHF photochromic system

1,1-Dicyano-dihydroazulene (DHA 1) is a light sensitive molecule, convertible into vinylheptafulvene (VHF 2) in a reversible manner, therefore a so-called molecular switch. The dihydroazulene core is particularly attractive because the multiple positions available for functionalization can generate diversity in terms of optical and switching properties of the photochromic system, rendering it appealing for a wide range of applications, from smart materials, to photo-responsive biological systems, to sensing. In recent years, this molecular switch has been considered a qualified aspirant for solar energy storage in closedcycle systems and the research has been directed towards tuning its energy storage capacity and developing new triggers to release the energy upon demand, possibly allowing recyclability of the system. In the present communication, we will give a general overview of the recent advances and the multiple approaches undertaken to study this photochromic system.