[Fe(pic) 3 ]Cl 2 ‚EtOH (pic ) 2-picolylamine) is a spin-crossover compound that can be converted from the low-spin state to the high-spin state at temperatures below the thermal transition temperature by way of light irradiation in the visible part of the electromagnetic spectrum. For this compound, the question regarding the quantum efficiency of this photoconversion process and its possible dependence on irradiation intensity gave rise to some controversy. The experimental results presented in this paper demonstrate that the quantum efficiency of the photoconversion at 11 K is on the order of unity, with no noticeable dependence on irradiation intensity. It does, however, depend to some extent on the fraction of complexes already converted to the high-spin state.

Efficient resonant energy transfer occurs within the R 1 line of the 4 A 2 f 2 E transition of the [Cr(ox) 3 ] 3chromophore in mixed crystal [Rh(bpy) 3 ][NaAl 1-x Cr x (ox) 3 ]ClO 4 (x ) 0.05-0.9, ox ) oxalate, bpy ) 2,2′bipyridine). This manifests itself in the form of multiline patterns in resonant fluorescence line narrowing (FLN) experiments at 1.5 K. The conditions for such a resonant process to occur are that the inhomogeneous line width of the R 1 line is larger than the zero-field splitting of the ground state, which, in turn, is larger than the homogeneous line width of the transition. The number of lines and their relative intensities depend critically upon the [Cr(ox) 3 ] 3concentration and the excitation wavelength within the inhomogeneous distribution. The basic model for resonant energy transfer as presented by von Arx et al. (Phys. ReV B 1996, 54, 15800) is extended to include the effects of diluting the chromophores in an inert host lattice and of nonresonant R 2 excitation. In addition, Monte Carlo simulations serve to explain the temporal evolution of the multiline pattern following pulsed excitation.