Photophysics of Octabutoxy Phthalocyaninato-Ni(II) in Toluene: Ultrafast Experiments and DFT/TDDFT Studies

Reported herein is a combination of experimental and DFT/TDDFT theoretical investigations of the ground
and excited states of 1,4,8,11,15,18,22,25-Octabutoxyphthalocyaninato-nickel(II), NiPc(BuO)8, and the
dynamics of its deactivation after excitation into the S1(π,π*) state in toluene solution. According to X-ray
crystallographic analysis NiPc(BuO)8 has a highly saddled structure in the solid state. However, DFT studies
suggest that in solution the complex is likely to flap from one D2d-saddled conformation to the opposite one
through a D4h-planar structure. The spectral and kinetic changes for the complex in toluene are understood in
terms of the 730 nm excitation light generating a primarily excited S1 (π,π*) state that transforms initially
into a vibrationally hot 3(dz2,dx2-y2) state. Cooling to the zeroth state is complete after ca. 8 ps. The cold (d,d)
state converted to its daughter state, the 3LMCT (π,dx2-y2), which itself decays to the ground state with a
lifetime of 640 ps. The proposed deactivation mechanism applies to the D2d-saddled and the D4h-planar structure
as well. The results presented here for NiPc(BuO)8 suggest that in nickel phthalocyanines the 1,3LMCT (π,dx2-y2)
states may provide effective routes for radiationless deactivation of the 1,3(π,π*) states.