Electronic property of Group IV phthalocyanine dimers: SiPcMPc

A series of Group IV phthalocyanine (Pc) dimers, (n-C₆H₁₃)₃SiOSiPcOSiPcOSi(n-C₆H₁₃)₃ (SiPcSiPc), (n-C₆H₁₃)₃SiOSiPcOGePcOSi(n-C₆H₁₃)₃ (SiPcGePc), and (n-C₆H₁₃)₃SiOSiPcOSnPcOH (SiPcSnPc), was characterized by cyclic voltammetry and DFT calculation. Two oxidations and two reductions were observed for (n-C₆H₁₃)₃SiOSiPcOSiPcOSi(n-C₆H₁₃)₃ and (n-C₆H₁₃)₃SiOSiPcOGePcOSi(n-C₆H₁₃)₃, while there were two oxidations and three reductions for (n-C₆H₁₃)₃SiOSiPcOSnPcOH. The Pc with a bigger size of the central metal in one part of the dimeric compound is more difficult to be oxidized but it is easier to be reduced at the same time: i.e., both oxidation and reduction potentials showed a positive shift with the increase of the size of the central metal atom. Density functional theory was used to optimize the structures of the Pc dimers and to understand the electrochemical properties. The optimized structures of HOSiPcOSiPcOH, HOSiPcOGePcOH and HOSiPcOSnPcOH as model compounds for SiPcSnPc, SiPcGePc, SiPcSiPc, respectively, show that all the Pc dimers are staggered, the plane-to-plane distances are 3.394, 3.538 and 3.722 Å, respectively. Tin generates a saddle-type structure of phthalocyanine, but silicon or germanium does not greatly distort the ring structure, and yields a planar ring structure. A large plane-to-plane distance and a high degree of plane distortion yield a red-shift of Q-band, a low ring current, high oxidation and low reduction potentials and high ionization energies.