Rw. Wagner et al., SYNTHESIS OF PORPHYRINS TAILORED WITH 8 FACIALLY-ENCUMBERING GROUPS -AN APPROACH TO SOLID-STATE LIGHT-HARVESTING COMPLEXES, Tetrahedron, 50(38), 1994, pp. 11097-11112
Synthetic models of the photosynthetic antenna complexes must achieve
long-range 3-dimensional order encompassing a large number of porphyri
nic pigments with limited direct contact of the pigments. In order to
develop solid-state antenna complexes, we have synthesized porphyrins
bearing benzyloxy groups projecting over both faces and optionally als
o around the periphery of the porphyrin. Routes have been established
for prefunctionalizing benzaldehydes with various benzyloxy groups. Re
action of 2,6-bis, 3,5-bis, or 2,4,6-tris(benzyloxy)benzaldehydes with
pyrrole via the room temperature two-step one-flask porphyrin reactio
n provides direct access to the facially-encumbered porphyrins. The be
nzyloxybenzaldehydes react as efficiently as methoxybenzaldehydes, ind
icating the utility of the -OCH2- unit for introducing large substitue
nts near the face of the porphyrin. The octakis and dodecakis(benzylox
y)porphyrins exhibit characteristic porphyrin absorption and fluoresce
nce properties in solution. The crystal structure of meso-tetrakis[2,6
-bis(2,3 4,5,6-pentafluorobenzyloxy)phenyl] porphyrin has been determi
ned. The pentafluorobenzyloxy substituents provide a cavity on each si
de of the porphyrin plane which has an approximate cylindrical shape w
ith a diameter of similar to 7.5 Angstrom and a height of greater than
or equal to 4.5 Angstrom. The porphyrin core parameters are those obt
ained for free base derivatives in which the inner hydrogen atoms are
ordered. Crystal data: a = 14.759(1) Angstrom, b = 25.519 (2) Angstrom
, c = 13.100(1) Angstrom, alpha = 100.04(1), beta = 99.83 (1), gamma =
88.25(1), V = 4767.3 (6) Angstrom(3), all measurements at 127 K, tric
linic, space group P-1(-), Z = 2 R(1)(F) = 0.097, for 10020 ''observed
'' data, and wR(2)(F-2) = 0.275 for 17761 total unique (all) data.