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.

The porphyrins (e.g., porphine, 1) are of ubiquitous biological importance and remain among the most widely studied of all known macrocycles. Increasingly, however, attention is being devoted to the study of larger pyrrole-containing macrocycles.Such larger systems, the so-called "expanded porphyrins",1 appear attractive with regard to a variety of biomedical applications ranging from magnetic resonance imaging (MRI)1-3 and photodynamic therapy (PDT)1•* 1234•5 to anion chelation and drug delivery.1•6While there are now a number of expanded porphyrins known,1 including penta-and hexapyrrolic macrocycles such as sapphyrin,7 pentaphyrin,8 hexaphyrin,9 and rubyrin,10 none is easy to prepare.

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