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]aneN(4)) 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]aneN(4))(CN)(2)]PF6 have also been prepared. Both are E-2(g) 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 mu s in aqueous solution which increases to 215 mu s upon macrocyclic N-H deuteration, whereas the corresponding lifetime of the [16]aneN4 complex is 25 mu s and is unaffected by macrocyclic N-H deuteration. The implications of the temperature dependence of the excited state lifetimes are also presented. (C) 2009 Elsevier B.V. All rights reserved.