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(,*) 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 D2dsaddled 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 (,*) state that transforms initially into a vibrationally hot 3(dz 2,dx 2 -y 2) state. Cooling to the zeroth state is complete after ca. 8 ps. The cold (d,d) state converted to its daughter state, the 3LMCT (,dx 2 -y 2), 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 (,dx 2 - y 2) states may provide effective routes for radiationless deactivation of the 1,3(,*) states.