Spectroscopic and electrochemical properties of cyclopalladated complexes based on dibenzo[a,c]phenazine
摘要:
Cyclopalladated complexes based on dibenzo[a,c]phenazine were studied by H-1 NMR and electronic absorption and emission spectroscopy, and cyclic voltammetry. Replacement of ethylenediamine by heterocyclic ligands scarcely affects the coordination-induced proton shifts of the diazine part of the cyclometalated ligand, but, as the basicity of chelated ligands decreases, the screening of protons of the carbanionic part of those cyclometalated ligands which is the most proximate to the coordination center regularly decreases. Cyclopalladation reveals itself in the following characteristic parameters of photo- and electro-induced electron-transfer processes: longwave absorption band, lambda(max) (437 +/- 7) nm and epsilon (3.0 +/- 1.5)x 10(3) l mol(-1) cm(-1), vibration-structured low-temperature luminescence resulting from spin-forbidden optical transition from the excited to ground state of the complex with the energy E-infinity (16.98 +/- 0.03) kK and the lifetime T (190 +/- 20) mu s, and reversible one-electron electroreduction wave with E-1/2 -(1.39 +/- 0.03) V.