A convenient synthesis of isocyclam and [16]aneN4 and the photophysics of their dicyanochromium(III) complexes

The syntheses of the tetraazamacrocyclic ligands 1,4,7,11-tetraazacyclotetradecane (isocyclam) and 1,5,9,13-tetraazacyclohexadecane ([16]aneN4) in two steps starting from the corresponding tetraamine and diethylmalonate is reported. The trans-dicyanochromium(III) complexes, trans-[Cr(isocyclam)(CN)2]PF6 and trans-[Cr([16]aneN4)(CN)2]PF6 have also been prepared. Both are 2Eg emitters with 0–0 band emission wavelengths at 721.2 and 704.8 nm, respectively. The isocyclam complex has a room temperature excited state lifetime of 147 μs in aqueous solution which increases to 215 μs upon macrocyclic N–H deuteration, whereas the corresponding lifetime of the [16]aneN4 complex is 25 μs and is unaffected by macrocyclic N–H deuteration. The implications of the temperature dependence of the excited state lifetimes are also presented.