Point-Dipole Approximation of the Exciton Coupling Model Versus Type of Bonding and of Excitons in Porphyrin Supramolecular Structures

Abstract

The application of the exciton coupling model to interacting porphyrin chromophores is discussed. Covalently bonded systems and ionic or electrostatically bonded homoassociates require different orientations of the transition dipole moments in order to explain the experimental results: according to the symmetry of the assembly for covalently bonded porphyrins, and assuming isolated chromophores for ionic bonded porphyrins. Further, for covalently bonded systems, an extended exciton coupling has been demonstrated, but the ionic systems are in agreement with non-extended couplings. The relation of these facts to a molecular description of solid-state Wannier-Mott or Frenkel excitons is briefly discussed.

Interactions between cationic surfactants and 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin tetrasodium salt as seen by electric conductometry and spectroscopic techniques

“…This protonation induces twisting from the near perpendicular orientation of the aryl substituents to a close coplanar conformation relative to the mean plane of the porphyrinate macrocycle [17]. The latter (twisted) particular disposition permits the formation of aggregates in an edge-to-edge disposition (J-aggregates) by interaction of the porphyrin protonated core with the anionic sulfonated moiety of another porphyrin (3) or in a face-to-face disposition (H-aggregates) by interaction of the overall macrocyclic rings (4) [18]. Thus the predominant species are [H 4 TPPS 2− ] monomers and J-aggregates conferring an intense green colour to the solution.…”

Non-covalent assemblies of negatively charged boronated porphyrins with different cationic moieties

“…5 and 6, respectively. Taking into account exciton coupling and allowed transitions [12,13], the transitions with the highest dipole moment, i.e., the Soret band in the case of porphyrins, are more affected. A red shift in the Soret band is predicted from head-to-tail association with in-line transition dipoles.…”

Asymmetric Photochemistry and Photochirogenesis

“…[23] Determinate mechanisms exploit the interaction of racemic substances with chiral physical driving forces, which cause the prevalence of one enantiomer. Some examples of such driving forces were reviewed recently [24] and include the adsorption on enantiomorphic surfaces of quartz [25] or calcite, [26] the directed vortex caused by the stirring of a liquid, [27] weak intermolecular forces, [28] spinpolarized electrons, [29] and circularly polarized light (CPL). New concepts and results on absolute asymmetric synthesis induced by photochemical reactions, presented at the Photochirogenesis Symposium in Osaka, Japan, in September 2001, appear to be encouraging.…”