Ja. Baiano et al., NONRADIATIVE DECAY IN RHENIUM(I) MONOMETALLIC COMPLEXES OF 2,3-DI(2-PYRIDYL)PYRAZINE AND 2,3-DI(2-PYRIDYL) QUINOXALINE, Journal of physical chemistry, 99(50), 1995, pp. 17680-17690
The photophysical properties of the low-lying, emissive metal to ligan
d charge transfer (MLCT) excited states of two series of complexes of
the type [Re(BL)(CO)(3)L](+) (BL = 2,3-di(2-pyridyl)pyrazine (dpp) and
2,3-di(2-pyridyl)quinoxaline (dpq); L = N-methylimidazole, trimethylp
hosphine, acetonitrile, and substituted pyridines) have been investiga
ted. These systems have been studied by emission spectroscopy, electro
nic absorption spectroscopy, infrared absorption spectroscopy, excited
state lifetime measurements, electrochemistry, and resonance Raman sp
ectroscopy of the emissive states. The results show that the rate cons
tant for nonradiative decay (k(nr)) is the dominant mode of excited st
ate relaxation and that the ''energy gap law'' for radiationless decay
in the weak coupling limit is obeyed by these two series of complexes
. The relative nonradiative decay rates have been evaluated utilizing
the parameters E(0), S-m, and Delta upsilon(1/2) Obtained from one-mod
e emission band-shape analysis and h omega(m). The h omega(m), values
were determined from a quantitative analysis of resonance Raman data o
f the emissive state. The h omega(m) values for both classes of comple
xes include contributions from a C=O stretching acceptor mode at ca. 2
020-2040 cm(-1), which is observed in the resonance Raman of all compl
exes. The results of this analysis show that the CO modes make a small
contribution to the overall nonradiative decay rate. The greater degr
ee of complex solvent interactions, as evidenced by large Delta upsilo
n(1/2) values, is the major factor in the large values of k(m), relati
ve to non-carbonyl-containing complexes.