Spectroscopic, photochromic and kinetic behavior of photo conversion of Aberchrome 540 in an ionic liquid media

Article abstract of DOI:10.1016/j.saa.2018.06.032

The photo-bleaching reaction of the chemical actinometer, Aberchrome 540, is reported for the first time in a series of ionic liquids (ILs). This fulgide in its C-form undergoes an opening reaction to yield its E-form, when it is irradiated with UV light at wavelengths >400 nm. The magnitude of bleaching was monitored spectrophotometrically and their kinetics evaluated, obtaining first-order rate constants (k_obs). The results obtained in different ILs suggest that changes in the rate constants (k_obs) of the opening reaction of Aberchrome 540 are mainly governed by weaker interactions such as coulombic (π* parameter) and Van der Waals interactions (δ_H ², parameter). In addition, the photochemical fatigue resistance was also studied in ILs media and compared with conventional solvents (benzene, toluene, etc.). In particular, we found that three different tendencies dependent on the ILs used exist. The first group of ILs where the reversibility of the fulgide is favored (for example, [Bmim][BF₄], [Bmim][PF₆] and [Bmim][OTf]), behaviour similar to conventional solvents. The second group corresponds to ILs where photo reversibility is partial; and finally, other group of ILs that prevented photo reversibility. It is proposed that depending on the ILs used, the stabilization of different forms of the fulgide can be controlled, thus resulting important in terms of choosing the appropriate ILs for a specific photochemical reaction.