LUMINESCENCE PROPERTIES OF RIGID, ROD-LIKE, DICHROMOPHORIC SPECIES - DINUCLEAR RU-OS TERPYRIDINE-TYPE COMPLEXES WITH 2.4 NM METAL-TO-METAL DISTANCE

The rigid, rod-like, dinuclear complex (Meph-tpy)Ru-II (tpy-ph-bco-ph- tpy)Os-II (tpy-phMe)(4+)(1), where the Ru(tpy)(2)(2+) and Os(tpy)(2)(2 +) moieties are separated by a -ph-bco-ph- spacer (tpy = 2,2':6'2''-te rpyridine; Meph = p-tolyl; ph = p-phenylene; bco = bicyclo[2.2.2]octan e), with a metal-to-metal separation distance of 2.4 nm has been synth esized. The bridging ligand provides strict control over the metal-to- metal distance owing to its rod-like and rigid structure. It has been prepared by a cross-coupling reaction between various building-blocks utilizing Suzuki's methodology. The heterodinuclear complex (1) was ob tained by stepwise coordination of ruthenium(ll) and osmium(ll). The l uminescence properties of 1 and its one-electron oxidized form (Meph-t py)Ru-II (tpy-ph-bco-ph-tpy)Os-III (tpy-phMe)(5+) (2) have been invest igated. The results obtained show that in room temperature solution th e lifetime of the Ru-based moiety (tau = 1.1 ns) is too short to allow the occurrence of energy (in the case of 1) or electron (in the case of 2) transfer to the Os-based moiety over the 2.4 nm metal-to-metal d istance, in a rigid matrix at 77 K, the lifetime of the Ru-based moiet y is much longer (tau = 10.5 mu s) Under such conditions, energy trans fer from the Ru-based to the Os-based moiety of 1 takes place with a r ate constant 4.4 x 10(6) s(-1). Electron transfer, however, does not o ccur in 2 because the necessary solvent repolarization is prevented by the rigid matrix.