A near-UV triplet emission from [Au(2)(dcpm)(2)](ClO(4))(2) has been discovered. Studies on the spectroscopic properties of the complexes [Au(2)(dcpm)(2)]Y(2) (Y=ClO(4)(-), PF(6)(-), CF(3)SO(3)(-), [Au(CN)(2)](-), Cl(-), and I(-); dcpm=bis(dicyclohexylphosphanyl)methane) support the assignment of the high-energy emissions at 360-368 nm to the (3)[dsigma*psigma] excited state, adducts of which exhibit exciplex emissions in the visible region with solvent or counterions (see schematic diagram).

The complexes [Au2(dcpm)2]-Y2 (dcpm = bis(dicyclohexylphosphino)methane; Y=ClO4 (1), PF6- (2), CF3SO3- (3), Au(CN)2- (4), Cl- (5), SCN (6) and I- (7)) were prepared, and the structures of 1 and 4-7 were determined by X-ray crystallography. Complexes 1-4 display intense phosphorescence with lambdamax at 360-368 nm in the solid state at room temperature as well as in glassy solutions at 77 K. The solid-state emission quantum yields of the powdered samples are 0.37 (1), 0.74 (2), 0.53 (3) and 0.12 (4). Crystalline solid 5 displays both high-energy UV (lambdamax = 366 nm) and low-energy visible emissions (lambdamax = 505 nm) at room temperature, whereas either 6 or 7 shows only an intense emission with lambdamax at 465 or 473 nm, respectively. All the complexes in degassed acetonitrile solutions exhibit an intense phosphorescence with lambdamax ranging from 490 to 530 nm. The high-energy UV emission is assigned to the intrinsic emission of the 3[dsigma*psigma] excited state of [Au2(dcpm)2]2+, whereas the visible emission is attributed to the adduct formation of the triplet excited state with the solvent/counterion. The quenching rate constants of the visible emission of [Au2(dcpm)2]2+ in acetonitrile by various anions are 6.08 x 10(5) (ClO4-), 9.18 x l0(5) (PF6 ), 1.55 x 10(7) (Cl-) and 4.06 x 10(9) (I-) mol(-1) dm3s(-1). The triplet-state difference absorption spectra of 1-4 in acetonitrile show an absorption band with lambdamax at 350 nm and a shoulder/absorption maxima at 395-420 nm; their relative intensities are dependent upon the halide ion present in solution. Substrate binding reactions of the 3[dsigma*psigma] excited state with halide (X-) to give [Au2(dcpm)2X]+* would account for the lower energy absorption maxima in the triplet-state difference absorption spectra. With iodide as the counterion, complex 7 undergoes a photoinduced electron-transfer reaction with I- to give the radical anion I2-.

The light intensity and concentration dependence of the photoproduct yield are investigated in a monophotonic process. The relationship of the photoproduct yield with the laser intensity and the complex concentration for a monophotonic process is derived under laser flash photolysis. The relationship is confirmed experimentally in a monophotonic process, i.e., triplet-triplet transition for a Cu͑I͒ complex Cu 6 ͑DMNSNЈ͒ 6 (DMNSNЈϭ4,6-dimethylpyrimidine-2-thiolate). At low light intensity, the relationship can be approximated by a linear inverse square root dependence on the light intensity. Based on this equation, a method is proposed to determine the intrinsic back electron transfer rate constant k ET b in photoinduced intermolecular electron transfer reactions, precluding the effect from the diffusional encounter pairs. The Marcus ''inverted region'' is observed by using the method in photoinduced back electron transfer reactions of ͓Au 2 ͑dppm͒ 2 ͔͑ClO 4 ͒ 2 (dppmϭbis͑diphenylphosphino͒methane) with a series of substituted pyridinium acceptors.

A near-UV triplet emission from [Au(2)(dcpm)(2)](ClO(4))(2) has been discovered. Studies on the spectroscopic properties of the complexes [Au(2)(dcpm)(2)]Y(2) (Y=ClO(4)(-), PF(6)(-), CF(3)SO(3)(-), [Au(CN)(2)](-), Cl(-), and I(-); dcpm=bis(dicyclohexylphosphanyl)methane) support the assignment of the high-energy emissions at 360-368 nm to the (3)[dsigma*psigma] excited state, adducts of which exhibit exciplex emissions in the visible region with solvent or counterions (see schematic diagram).

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