C. Chiorboli et al., Photophysics of dinuclear Ru(II) and Os(II) complexes based on the tetrapyrido[3,2-a : 2 ',3 '-c : 3 '',2 ''-h : 2 '''-3 '''-j]phenazine (tpphz) bridging ligand, INORG CHEM, 38(10), 1999, pp. 2402-2410
The photophysical properties of mono- and dinuclear complexes based on the
bridging ligand tpphz (tpphz = tetrapyrido [3,2-a:2',3'-c:3 ",2 "-h:2"'-3"'
-j]phenazine) were investigated. The complexes are of general formula [M(bp
y)(2)(tpphz)](2+) [M = Ru(II), Os(II)] and [(bpy)(2)M-1(tpphz)M-2(bpy)(2)](
n+) [M-1 = M-2 = Ru(II), n = 4; M-1 = M-2 Os(II), n = 4; M-1 = Ru(II), M-2
= Os(II), n = 4; M-1 = Ru(II), M-2 = Os(III), n = 5]. The tpphz bridging li
gand, being aromatic, rigid, and planar, has interesting structural feature
s for the design of covalently linked donor-acceptor systems. In this work
particular attention was devoted to the electronic properties of this bridg
e and their effect on the photophysical behavior. All of the results are co
nsistent with direct involvement of the tpphz bridge in the photophysically
active, lowest MLCT excited states. Relevant findings are as follows: (i)
in mononuclear complexes, MLCT excited-state energies are highly sensitive
to interactions at the free bpy-like end of the tpphz ligand, such as metal
ation and protonation; (ii) in thp dinuclear complexes, the electronic grou
nd state behaves as a valence-localized, supramolecular system, while a sub
stantial amount of intercomponent electronic coupling is indicated by MLCT
excited-state behavior; (iii) in the heterodinuclear complex, fast (k > 10(
9) s(-1)) energy and/or electron transfer processes take place across the t
pphz bridge.