Investigating the effects of solvent on the ultrafast dynamics of a photoreversible ruthenium sulfoxide complex.

The photochromic complex [Ru(bpy)2(pySO)](2+) [pySO is 2-(isopropylsulfinylmethyl)pyridine] undergoes wavelength specific, photoreversible S → O and O → S linkage isomerizations. Irradiation of the ground state S-bonded complex with blue light produces the O-bonded isomer, while irradiation of the O-bonded isomer with green light produces the S-bonded isomer. Furthermore, isomerization time constants are solvent-dependent. Ultrafast transient absorption spectroscopy has been employed to investigate the relaxation processes that lead to S → O isomerization in 1,2-dichloroethane, propylene carbonate, and ethylene glycol. The isomerization is most rapid in 1,2-dichloroethane and slowest in ethylene glycol. Photochemical reversion of the O-bonded isomer in propylene carbonate has further been investigated and indicates similar relaxation or isomerization kinetics, though the excited states that lead to isomerization are distinct between the S- and O-bonded isomers.