Preparation, Photochemistry, and Electronic Structures of Coumarin Laser Dye Complexes of Cyclopentadienylruthenium(II)

The syntheses and characterization of six new compounds that contain the CpRu⁺(Cp = η⁵-C₅H₅) moiety bound to a substituted coumarin laser dye are reported. The complexes prepared are of the general form [CpRu(η⁶-laser dye)]PF₆, where laser dye = coumarin-1 (7-(diethylamino)-4-methylcoumarin), coumarin-2 (4,6-dimethyl-7-(ethylamino)coumarin), coumarin-6 (3-(2-benzothiazolyl)-7-(diethylamino)coumarin), coumarin-311 (7-(dimethylamino)-4-methylcoumarin), coumarin-334 (10-acetyl-2,3,6,7-tetrahydro-1H,5H,l lH-[l]benzopyrano[6,7,8-(ij]quinolizin-l0-one), or coumarin-338 (2,3,6,7-tetrahydro-l 1-oxo-lH,5H,l1H-[l]benzopyrano[6,7,8-ij]quinolizine-10-carboxylic acid 1,1-dimethylethyl ester). The structures of all of the new complexes except the complex of coumarin-6 were determined by^lH and¹³C NMR spectroscopy and contain the CpRu⁺group bound to the benzenoid moiety of the coumarin system. The CpRu⁺group binds to the benzothiazole group of the coumarin-6 compound. Photolysis of the complexes in CH₃CN solutions results in the formation of CpRu(CH₃CN)₃⁺ and the free dye. The complexes of the dyes other than coumarin-6 exhibit low-lying MLCT bands and are not emissive. The coumarin-6 complex retains the low-lying intramolecular charge-transfer band present in the free dye and emits in fluid solution at room temperature with ⋋_max= 532 nm and Φ = 0.11 ± 0.02. The laser dye centered emission band of the complex is red-shifted 25 nm with respect to the free coumarin-6 emission.