Emission Studies of Transition-Metal Complexes of 2,2’-Dlpyridylamlne. 1. Bis

Emission Studies of Transition-Metal Complexes of 2,2’-Dlpyridylamlne. 1. Bis

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2080 J. Phys. Chem. 1981, 85, 2080-2086 Emission Studies of Transition-Metal Complexes of 2,2’-Dlpyridylamlne. 1. Bis Complexes of Rhodium(II1) and Irldium(II1) Wen Liang Huang, Donald P. Segers, and M. Kelth DeArmond’ Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27650 (Received: October 6, 1980; In Final Form: April 6, 198 1) Luminescence spectra, lifetimes, and polarization spectra have been measured for the [Rh(HDPA)zC1z]+ and [Ir(HDPA)&l2]+ complexes (HDPA = 2,2’-dipyridylamine). The complexes in acidic or neutral solution each show a broad, symmetric, and structureless red emission with microsecond lifetime assigned a dd* phos- phorescence. In strong basic solution, the deprotonated complexes exhibit a blue asymmetric emission with a long tail overlapping the red-emission band. This blue emission shows no vibrational structure and has a lifetime on the order of microseconds. This emission is 0.35-pm-’ blue shifted with respect to the red emission and 0.56-pm-’ red shifted with respect to the phosphorescence of the ligand in strong basic solution. This emission can be assigned as charge-transfer dn* emission analogous to that for the [Ru(bp~)~]~+ complex or as lig- and-localized nn* emission. Such a dn* emission from a Rh(II1) complex would be unique. The emission polarization for the red dd* emission exhibits a nonzero slope across the band; moreover, the lifetime also varies with emission wavelength. This anomalous behavior is apparently intrinsic to dd* emission since similar data are obtained for the dd* emission of the previously studied [Rh(phen)zC12]+ complex. The origin of this unique behavior is not apparent but could have its origin in (1) solvent-induced barriers (distortions) in the emitting state and/or (2) intrinsic differences in vibrational relaxation rates with the emitting state. Introduction The chemistry of the bidentate ligand 2,2’-dipyridyl- amine (HDPA) and its coordination complexes with such metal ions as nickel(II),’ copper(II),z ir~n(II),~ cobalt(I1) and -(111),436 palladium(II),6 and rhodium(II1) and iridi- u~(III)~ has been studied. However, no luminescence has been reported for any HDPA complex while, in contrast, the luminescence and excited-state reactivity of the related 2,2’-bipyridine (bpy) and 1,lO-phenanthroline (phen) complexes of d6 metal ions (particularly Ru(I1) and Rh- (111)) have been the subject of a number of A large portion of the interest in these materials as been motivated by the desire to use these complexes in photo- catalytic water-splitting reaction~.~~’~ The successful splitting of H20 in a heterogeneous systemI7 using [Ru- (bpy),Jz+ will not likely diminish interest in the lumines- cent materials as photocatalysts but will stimulate a search for better and cheaper photocatalysts. For example, the light scattering associated with the heterogeneous catalyst system (due to colloidal metal catalyst) suggests that a (1) Burbridge, C. D.; Goodgame, D. M. L. J.
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Emission Studies of Transition-Metal Complexes of 2,2’-Dlpyridylamlne. 1. Bis

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