Photoluminescent and crystal structure properties of the yellow and orange forms of [Re2(m-Cl)2(CO)6(m- 4,5-trimethyl-silyl-pyridazine]

A series of neutral, dinuclear, luminescent rhenium(I) complexes suitable for phosphorescent organic light emitting devices (OLEDs) has been recently reported1,2. These compounds, of general formula [Re2(μ-Cl)2(CO)6(μ-1,2-diazine)], contain diazines bearing alkyl groups in one or in both the b positions. The complexes show intense green/yellow emissions in toluene solution and in the solid state and some of the complexes possess, in solution, high emission quantum yields (F 0.18-0.22 for the derivatives with disubstituted diazines). The excited state responsible for this emission can be confidentially described as a triplet metal-to-ligand charge transfer (3MLCT) level3. Following the DFT computational suggestions we have now synthetized a new complex of this family using the 4,5-bis(trimetylsilyl)-1,2-diazine ligand namely [Re2(m-Cl)2(CO)6(m- 4,5-trimethyl-silyl-pyridazine] (1, see Scheme). This complex has been completely carachterized in solution and it shows an emission maximum batochromically shifted respect to those of the analogous Re(I) compounds with alkyl-substituted diazine, with a lower quantum yield. Slow evaporation at room temperature of a CH2Cl2 solution containing (1) induces the concomitant formation of orange and yellow single crystals (Figure 1, top). X-ray crystal structure determinations performed at room temperature as well as at 100 K, show that they are two different polymorphs of the same compound. The emission spectra recorded on crystalline samples of the two polymorph (Figure 1, bottom) are hypsochromically shifted respect to the solution one and present higher quantum yields (lem = 537 nm and F = 0.30 for the yellow phase, lem = 575 nm and F = 0.50, for the orange one). References (1) Mauro, M, Quartapelle Procopio, E., Sun,Y., Chien, C-H., Donghi, D., Panicati, M., Mercandelli, P., Mussini, P., D’Alfonso, G., De Cola, L. Adv. Func. Mat. 2009, in press (2) Donghi, D., D’Alfonso, G., Mauro, M, Panigati, M., Mercandelli, P., Sironi, A., Mussini, P., D’Alfonso, L., Inorg. Chem. 2008, 47, 4243. (3) Wrighton, M., Morse, D. L., J. Am. Chem. Soc., 1974, 96, 998.