A model photosynthetic antenna consisting of four covalently linked zinc tetraarylporphyrins, (PZP)3−PZC, has been joined to a free base porphyrin-fullerene artificial photosynthetic reaction center, P−C60, to form a (PZP)3−PZC−PC60 hexad. As revealed by time-resolved absorption and emission studies, excitation of any peripheral zinc porphyrin moiety (PZP) in 2-methyltetrahydrofuran solution is followed by singlet−singlet energy transfer to the central zinc porphyrin to give (PZP)3−1PZC−P−C60 with a time constant of ∼50 ps. The excitation is passed on to the free base porphyrin in 240 ps to produce (PZP)3−PZC−1P−C60, which decays by electron transfer to the fullerene with a time constant of 3 ps. The (PZP)3−PZC−P•+−C60 •- charge-separated state thus formed has a lifetime of 1330 ps, and is generated with a quantum yield of 0.70 based on light absorbed by the zinc porphyrin antenna. The complex thus mimics the basic functions of natural photosynthetic antenna systems and reaction center complexes.

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A new. general synthesis of the first /?-substituted tetra-and hexaalkyl terpyrroles is described. Also described are two new classes of expanded porphyrins derived from the hexaalkyl terpyrrole. The key step in the terpyrrole formation is the copper(i1)-mediated oxidative coupling of the LDA-derived enolates of a-keto pyrroles. The first new expanded porphyrin reported here, the so-called "orangarin", contains five new class of expanded porphyrins, the pyrrolic subunits and two bridging carbon "arnethyrins", are 24n-electron nonaroatoms, and is formally a 20n-electron matic macrocycles containing six pyrrole nonaromatic macrocycle.

40π‐Electrons and ten pyrrole units are found in macrocycle 1, the largest expanded porphyrin reported thus far. The tetrahydrochloride salt of 1 was characterized in solution and in the solid state. These investigations indicate that the macrocycle exists as a pair of enantiomers whose chirality arises from a twist of the ring.

COMMUNICATIONS [7] Crystal structure analyses. colorless crystals of 3a and 15 were investieated on a lour-circle diffractometcr (CAD4, at -80 'c' with Cu,, radiation ( 2 =154.178 pm). 3a: C,,H,,B,Li,SiZ.2THF. crystal dimensions 0 6 x 0.3 x 0.2 inm'. monoclinic. space group P2,c. Z = 4. (I = 9 7 2 3 2 ) . h = 1173.5(2). <' = 2890.7(6) pm. / I = 98.45(3) . Vr7 = 3262.1 x lO-"m', pca,Ld = 0.99X gcm -'; 3994 measured reflections in the range up to 20 = 110 (w scans). 3903 of which \+ere independent and were used for the further calculati~ns alter Loreiitz and polarization correction: no absorpt~on correction 111 = I 1 Ocm-') The structure was solved by direct methods and refined against the ti: data xith full matrix. A disorder showing up in the differenceFourlei-5yntheses was accounted for bq a "split atom model" where a C 5 -SiMe, group superposes the B3-iBu unit at 8 3 and. vice versa. a B3-/Bu group superposes the C5-SiMe3 unit at C 5 . Due to these superpositions. geometrrc restraints olihe B C (160 pm) and Si-C (187 pm) bond length wcrc used during refinement. and the temperature factors of atoms approaching each other were defined to be equal. In this way good conbergence and a maximal residual electron density 0.35 e k ' were achieved. The distribution of the alternative arrangements of the molecules was determincd to be 59.3(4) aiid 40.7%). The H a t o m u'ere localized iii part by dillerence Fourier syntheses: the others were calculated; they were included in the calculation riding on their bonding partners and with isotropic temperature factors coinmon by gsoups. Anisotropic teinpcratui-e factors %ese used foi-all the remaining atom& except C 7 . wRi = 0.2066 (SHELX 93 program). corresponding to R = 0.069 for 2951 reflections with &>4u(F,>). inanimal residual electron density 0.33 e k ' . -15: C,,H,,B,Si,, crystal dimcnsions 0.7 x 0.3 x 0.2 n1m3, monoclinic. space group P2,:n. Z = 4. ci = 928.9(2). h = 1655,2(3). c = 2154.4(4) pin. /) = 92.80(3) , VF7 = 3308.5 x I O -" in'. pc,,L6 = 1.009 gcni-'; 4461 reflections iii the range up to 211 =110 ( ( , I scans), 4157 of wliicli were independent 41 54 reflections \+ere used foi-further calculations after Lorentr aiid polarizatioii correction. the structure solutioii and refinement a s for 3 a led to wR,=0.1955, corresponding to R = 0.064 for 2123 reflections uith ti) > 40(&,). and ;I maximal residual electron densit) of 0 34 e k ' . Further details of the crystal structure investigations inay be obtained from the Fachiiiformationsreiitrum Karlsruhe. D-76344 Eegenstein-Leopoldslitifeii (FRG). on quoting the depository number CSD-58435.