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 S-1(pi,pi*) 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 D-2d-saddled conformation to the opposite one through a D-4h-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 S-1(pi,pi*) state that transforms initially into a vibrationally hot (3)(d(z2),d(x2-y2)) state. Cooling to the zeroth state is complete after ca. 8 ps. The cold (d,d) state convened to its daughter state, the (LMCT)-L-3 (pi,d(x2-y2)), which itself decays to the ground state with a lifetime of 640 ps. The proposed deactivation mechanism applies to the D-2d-saddled and the D-4h-planar structure as well. The results presented here for NiPc(BuO)(8) suggest that in nickel phthalocyanines the (LMCT)-L-1,3 (pi,d(x2-y2)) states may provide effective routes for radiationless deactivation of the (1,3)(pi,pi*) states.