Photophysical and Photochemical Properties of Viologen-Linked N-Alkylporphyrin Diads and Their Metal Complexes

Photoinduced electron transfer upon supramolecular complexation of (porphyrinato)Sn-viologen with cucurbit[7]uril

The synthesis of (porphyrinato)Sn-viologen, 1, and its supramolecular complexation with cucurbit[7]uril (CB[7]) were studied. ¹H NMR spectroscopic studies obviously reveal that 1 forms a 1 : 2 supramolecular complex with CB[7] through the inclusion of viologen moieties of 1 into the cavity of CB[7]. The cyclic voltammetric study supports that the binding affinity of the radical cation forms is comparable to that of the di-cation viologen toward CB[7]. The fluorescence arising from the porphyrin moiety is significantly quenched upon the complexation of 1 with CB[7]. The ps-time-resolved fluorescence and ns-transient absorption spectroscopic studies reveal that the photoinduced electron transfer (PET) between viologen and Sn(iv) porphyrin of 1 takes place from the first excited singlet (S₁) state and the second excited triplet (T₂) state of the porphyrin moiety upon complexation with CB[7], while the PET from the S₁ state is negligible in the absence of CB[7].

Kinetics and mechanisms of the formation of a sitting-atop complex of N-alkylporphyrin with Al(III) in moist acetonitrile

The formation of a sitting-atop complex of a N-alkylporphyrin, containing a 6-hydroxyhexyl group, with Al 3+ was studied in moist acetonitrile by equilibrium and kinetic measurements. A sandwich type of metalloporphyrin, where a metal ion binds two N-alkylporphyrins, appears to be formed under the conditions that porphyrins exist in excess over a metal ion. When a large excess of metal ion was used, a 1:1 type of sitting-atop complex of Al(III) N-alkylporphyrin was produced through formation of the sandwich type of Al(III) N-alkylporphyrin.

Synthesis and spectroelectrochemistry of N-cobaltacarborane porphyrin conjugates

N-Substituted porphyrins are well-known for the distortion they exhibit of the porphyrin plane through the sp(3) hybridization of one of the pyrrolenic units. They have served as model compounds in investigations of many biochemical processes. In this paper, we developed an efficient route to N-substituted porphyrins, and report the synthesis of a series of new N-substituted cobaltacarborane-porphyrins containing one or two cobaltabisdicarbollide anions linked by (CH(2)CH(2)O)(2) chains to either the core porphyrin nitrogens or to a meso-aminophenyl group. These conjugates show different degrees of distortion of the porphyrin macrocycle, which affect their spectroscopic and electrochemical properties. In particular, the core N-substituted conjugates show significant fluorescence quenching in comparison with the noncore substituted macrocycles. The X-ray structures of two targeted core N-cobaltacarborane porphyrin conjugates are presented. The electrochemical and spectroelectrochemical properties of these porphyrin conjugates were investigated; while the peripheral N-substituted cobaltacarboranylporphyrins undergo three reversible reductions and three reversible oxidations (two attributed to the porphyrin and one to the Co(III) cluster), the core N-substituted porphyrins exhibit complicated electrochemical behavior with coupled chemical reactions.