Photochemistry of Anthracene-Appended Cobalt(III) Cyclam Complexes

Abstract

The photochemistry of two anthracene-appended cobalt(iii) cyclam complexes is explored with a view to demonstrate a photoactivated ligand release process. The ligand exchange processes that occur in the complexes cis-[CoL(NO2)(ONO)]+ and trans-[CoL(NO2)(ONO)]+ in which L = 6-(anthracen-9-ylmethyl)-1,4,8,11-tetraazacyclotetradecane were monitored upon illumination of the anthracenyl chromophore at 360 nm in the presence of a large excess of thiocyanate. The trans-[CoL(NO2)(ONO)]+ complex underwent a ligand exchange reaction in the absence of light and displayed an enhancement of the reaction upon illumination. In contrast the cis-[CoL(NO2)(ONO)]+ complex was stable in the dark but displayed a significant quantum yield of photoactivated ligand release (Φ = 0.19). It is proposed that in cis-[CoL(NO2)(ONO)]+ the photoexcited anthracenyl chromophore undergoes efficient energy transfer to the cobalt(iii) cyclam before ligand exchange. Complexes based on the anthracenylcyclam–cobalt(iii) framework may be potentially useful candidates as photoactivated ligand release systems.