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.

Graphical abstractNew two step syntheses of 1,4,7,11-tetraazacyclotetradecane (isocyclam) and 1,5,9,13-tetraazacyclohexadecane ([16]aneN4), starting from the corresponding tetraamine and diethylmalonate, are reported. The dicyanochromium(III) complexes of these ligands have also been prepared and characterized photophysically.Figure optionsDownload full-size imageDownload as PowerPoint slide