Zinc chlorins for artificial light-harvesting self-assemble into antiparallel stacks forming a microcrystalline solid-state material.
We introduce a concept to solve the structure of a microcrystalline material in the solid-state at natural abundance without access to distance constraints, using magic angle spinning (MAS) NMR spectroscopy in conjunction with X-ray powder diffraction and DFT calculations. The method is applied to a novel class of materials that form (semi)conductive 1D wires for supramolecular electronics and artificial light-harvesting. The zinc chlorins 3-devinyl-3(1)-hydroxymethyl-13(2)-demethoxycarbonylpheophorbide a (3',5'-bis-dodecyloxy)benzyl ester zinc complex 1 and 3-devinyl-3(1)-methoxymethyl-13(2)-demethoxycarbonylpheophorbide a (3',5'-bis-dodecyloxy)benzyl ester zinc complex 2, self-assemble into extended excitonically coupled chromophore stacks. (1)H-(13)C heteronuclear dipolar correlation MAS NMR experiments provided the (1)H resonance assignment of the chlorin rings that allowed accurate probing of ring currents related to the stacking of macrocycles. DFT ring-current shift calculations revealed that both chlorins self-assemble in antiparallel pi-stacks in planar layers in the solid-state. Concomitantly, X-ray powder diffraction measurements for chlorin 2 at 80 degrees C revealed a 3D lattice for the mesoscale packing that matches molecular mechanics optimized aggregate models. For chlorin 2 the stacks alternate with a periodicity of 0.68 nm and a 3D unit cell with an approximate volume of 6.28 nm(3) containing 4 molecules, which is consistent with space group P2(1)22(1).
Ganapathy
Swapna
S
Leiden Institute of Chemistry, Einsteinweg 55, 2333CC Leiden, The Netherlands.
Sengupta
Sanchita
S
Wawrzyniak
Piotr K
PK
Huber
Valerie
V
Buda
Francesco
F
Baumeister
Ute
U
Würthner
Frank
F
de Groot
Huub J M
HJ
D008027:Light; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D011166:Porphyrins / Q000737:chemistry*; D014961:X-Ray Diffraction; D015032:Zinc / Q000737:chemistry*
D011166:Porphyrins; C006969:chlorin; D015032:Zinc