Multiple Interactions in the Self-Association of Porphyrin Discotic Mesogens

Abstract

The conformational preferences and the self-associational behaviors of two hemin-derived porphyrin compounds, a tetramethyl ester and a liquid crystalline tetrakis(3,5-didodecyloxyphenyl)ester, have been studied by UV/vis and (1)H NMR spectroscopy in solution. Results indicate that the 3,5-didodecyloxyphenyl units play an important role in both the conformational and the self-associational behaviors of the mesomorphic tetraester. In the monomeric, nonassociated species, the two propionic 3,5-didodecyloxyphenyl esters establish mutual CH/pi interactions that restrict the fluctuative behavior of the chains. In the dimeric, self-associated species, intermolecular CH/pi interactions occur in addition to the pi-pi stacking of the porphyrin cores. The temperature-dependent addition of side CH/pi interactions to the pi-pi stacking of the porphyrin rings accounts for the observed tightening and for the slower dynamics of the dimeric structure. The relationship between the self-associational behavior and the mesomorphism of the hemin-derived porphyrin tetraesters is also discussed.

Relevance of Weak Hydrogen Bonds in the Conformation of Organic Compounds and Bioconjugates: Evidence from Recent Experimental Data and High-Levelab InitioMO Calculations

“…Recent papers reporting on the relevance of CH/π hydrogen bonds include a polycyclic succinimide, 172 a crown ether derivative, 173 an azacalix [4]arene derivative, 174 molecular tweezers with longchain alkyl chains and naphthalene rings, 175 182 metal complexes of H(Aib-∆Phe) 2 -Aib-OCH 3 , 183 and a heminderived porphyrin compound. 184 In every case, when examined, the crystal conformation was found to be maintained in solution. (See our previous reviews [43][44][45] for other examples in more complex molecules.…”

“…As shown in the preceding section, there are sufficient data showing the importance of the CH/π hydrogen bond in making the folded structure stable. Recent papers reporting on the relevance of CH/π hydrogen bonds include a polycyclic succinimide, a crown ether derivative, an azacalix[4]arene derivative, molecular tweezers with long-chain alkyl chains and naphthalene rings, a rhenium complex ( fac -[Re(bpy)(CO) 3 (PR 3 )] + ), a crown-tetrathia[3.3.3.3]metacyclophane, 2,11-dithia[3]paracyclo[3](4,4′)-2,2′-bipyridinophane, N , N ′-bis(2-tosylaminobenzylidene)-1,4-xylylenediamine complexes, [Pd(η 3 -2-Me-allyl)(μ-Ph 2 PPy)] 2 (BF 4 ) 2 , [Pd( C 2 , N -dmba)(μ-N 3 )] 2, 1,4-bis(2-hydroxymethyl-5,5-dimethyl-1,3-dioxan-2-yl)benzene, metal complexes of H(Aib-ΔPhe) 2 -Aib-OCH 3 , and a hemin-derived porphyrin compound . In every case, when examined, the crystal conformation was found to be maintained in solution.…”

Dendron-Mediated Self-Assembly, Disassembly, and Self-Organization of Complex Systems

“…1073,1074 The model was later refined by both solid-state XRD and solution-phase UV-vis and 1 H NMR experiments to propose a schematic model of the two Φ h mesophases (Figure 309). 1075 The high-temperature phase is a classic representation of the Φ h phase and is driven by the cofacial π-π interactions of stacked macrocycles, with each macrocycle offset in both the H10-20 and H5-15 axis of the macrocycle. This model was first proposed by Sanders 1076 and demonstrated in a nondendronized β-substituted porphyrin by Costa and Dalcanale.…”

“…At temperatures below 60 °C, the π-π stacking is not strong enough to offset the cost of the planar structure. 1075 Vinogradov developed poly(L-glutamate) dendronized porphyrins and Newkome dendronized tetrabenzoporphyrin that can be utilized as pH nanosensors (Figure 310). 1078 These dendronized porphyrins and tetrabenzoporphyrins are membrane-impermeable and have nonoverlapping emission that is modulated by pH titration of porphyrin cores.…”

“…The lower-temperature less-ordered phase arises from trimeric aggregates of macrocycles stabilized not only by cofacial π−π interactions but also by CH−π interactions arising from conformational changes in the phenyl propionic chain. At temperatures below 60 °C, the π−π stacking is not strong enough to offset the cost of the planar structure …”