Dynamics and mechanism of spin-state interconversion in transition metal complexes. (Volumes I and II)

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1992

OSTI ID:7102291

McCusker, J K

The kinetics of the [Delta]S = 2 spin-state interconversion in d[sup 6] transition metal complexes are examined. A series of compounds having a polypyridyal-based ligand framework are described which allow for systematic modification of molecular geometry. A nanosecond time-resolved laser spectrometer was constructed to measure the kinetics of spin-state interconversion as a function of temperature in an attempt to probe the molecular mechanism of [sup 5]T[sub 2] [yields] [sup 1]A[sub 1] relaxation is further supported by theoretical analyses. Fitting of variable-temperature kinetic data to classical, semi-classical, and quantum-mechanical theories of electron transfer give identical results, indicating that the quantum nature of the vibrational mode coupled to spin-state interconversion does not manifest itself in the 160-300 K range. This observation is inconsistent with coupling to a metal-ligand stretching mode and strongly suggests the involvement of low-frequency mode(s) (<100 cm[sup [minus]1]) such as a trigonal or rhombic twist. The mechanism of photo-induced formation of the [sup 5]T[sub 2] state upon photolysis of the low-spin species is also examined. Variable probe-wavelength transient kinetic studies are used in conjunction with variable-temperature electronic absorption spectra to definitively establish that the [sup 5]T[sub 2] state is formed in [le]700 fs following [sup 1]MLCT [l arrow] [sup 1]A[sub 1] excitation. The results indicate that the rate of intersystem crossing exceeds the rates of both internal conversion and vibrational relaxation, in stark contrast to previously held notions.

• Research Organization: Illinois Univ., Urbana, IL (United States)
• OSTI ID: 7102291
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical &amp; Physicochemical Properties
COMPLEXES
CONVERSION
ENERGY LEVELS
EXCITED STATES
ROTATIONAL STATES
TRANSITION ELEMENT COMPLEXES