Substituent Effects at the 5,10‐Positions of Dianilinotripyrrins on Their Dimerization Themodynamics

Abstract

Control of the association behavior by molecular design is one of the most essential benefits in artificial supramolecular systems. 1,14‐Dianilinotripyrrin has recently emerged as a novel conjugated molecule which forms a double helix in non‐polar solvents with the aid of multiple interstrand hydrogen bonding interactions. In this work, we investigated the substituent effects at the 5,10‐positions of tripyrrin on their association thermodynamics. This study illuminated two key findings; 1) electronic tuning by the para‐substituents reduce the entropic costs thereby slightly improve the association constants, and 2) ortho‐substituents force the tripyrrin core to be relatively planar, which significantly decreases the association constant due to less feasible π‐stacking.

meso-Aryl substituents modify the electrochemical profile and palladium(ii) coordination of redox-active tripyrrin ligands

“…Indeed, the bulky pentafluorophenyl substituents also led to an essentially planar tripyrrin unit in the case of α,α′-dianilinotripyrrins. 40 Lacking the NH hydrogen-bonding donors of the aniline derivatives, 10,40 however, HTM C6F5 does not adopt a double helical arrangement. Instead, the HTM C6F5 ligands pack in a herringbone pattern with pairs of ligands oriented in antiparallel fashion.…”

Synthesis and Dynamic Behaviors of 5,7,8,10-Tetraphenyl-1,14-dianilinotripyrrins

“…15 16 The 1,14-dianilinotripyrrins exhibited various structural changes in response to the environment. 17 18 19 For example, dianilinotripyrrin 1a displayed a double helical structure in nonpolar solvents, while a monomeric helix form was observed in the solid state obtained by evaporation of the solution in EtOH (Scheme 1a ). 15 The double helical form was not preferred if the terminal substituents are sterically demanding [e.g., 1,14-di(1-naphthyl)tripyrrin].…”

“…By contrast, the substituent effect at the 5,10-positions of the tripyrrin core was found to be not so significant, likely causing a small steric effect; K D = 140 M –1 at 293 K in CDCl 3 for tripyrrin 2a bearing 3,5-di- tert -butylphenyl groups at the 5,10-positions. 17 Curiously, pentafluorophenyl-substituted tripyrrin 2b showed an equilibrium between monomeric and dimeric forms only in cyclohexane. Ineffective π-stacking mode between the two tripyrrin cores as indicated in its X-ray structure may be a reason for this dynamic behavior.…”

“…Finally, bromination of 8 at the 1,14-positions was accomplished with NBS in THF at low temperature, followed by quick oxidation with DDQ, according to our previously reported reaction sequence. 15 17 Purification by column chromatography on silica gel gave 3 as a pure solid in 92% yield. Notably, 3 was stable in the solid-state and storable for several months in the fridge.…”

“…The solvent-dependent structural change was previously reported for 1a , which concluded that the monomeric form was favored against the dimeric form due to the hydrogen bonding with solvent molecules at the terminal aniline NH site. 15 , 17 18 19 By comparing the peak pattern, the 1 H NMR spectrum of 4a in CDCl 3 is assignable to its dimeric form and that in DMSO- d 6 to its monomeric form. It is notable that 4a exhibits only dimer-derived peaks in CDCl 3 , while 1a is in equilibrium between monomeric and dimeric forms in CDCl 3 ( K D = 270 M –1 at 298 K).…”