  We demonstrate the tip induced control of the spin state of copper
phthalocyanine (CuPc) on an insulator coated substrate. Accounting for
electronic correlations, we find that, under the condition of energetic
proximity of neutral excited states to the anionic groundstate, the system can
undergo a population inversion towards these excited states. The resulting
state of the system is accompanied by a change in the total spin quantum
number. Experimental signatures of the crossover are the appearance of
additional nodal planes in the topographical STM images as well as a strong
suppression of the current near the center of the molecule. The robustness of
the effect against moderate charge conserving relaxation processes has also
been tested.
