J-aggregate formation of a water-soluble porphyrin in acidic aqueous media

Abstract

J aggregate of a water-soluble porphyrin, 5,10,15,20-tetra(4-sulfophenyl)porphyrin (H2TPPS44−), formed in acidified aqueous solutions, exhibits sharp and intense absorption bands at 491 and 707 nm. These characteristic transitions, J bands, are of linear oscillators polarized in the long axis of rodlike aggregate. The molecules in the aggregate stack so as to lift the degeneracy of the porphyrin planar oscillator excited states. Measurements of flow-induced linear dichroism, circular dichroism, magnetic circular dichroism, as well as polarized fluorescence excitation spectra provide evidence not only of linear oscillator character of the intense J band at 491 nm, but also of presence of another diffuse absorption band around at 420 nm polarized in the short axis of the aggregate, which is the counterpart of the 491 nm band of porphyrin Soret origin. Extrinsic circular dichroism is induced upon addition of L-tartaric acid or by mechanical swirling flow in the period of aggregate growth. Resonance Raman spectrum of the aggregate is rather similar to that of the monomeric diacid except the polarization. The observed shifts of Raman peaks to lower frequency are ascribed to a deformation of porphyrin moiety and/or hydrophobic interaction between component molecules in the aggregate. The sharp and intense J bands polarized in the long axis of aggregate cannot be well described without taking into account the participation of interporphyrin charge resonance excited states, whereas the broadbands polarized in the short axis are exclusively ascribed to exciton resonance excited states. The porphyrin J band is characterized as sustaining an exchange narrowing by fast migration of excitation over the whole system of chromophores in a linear array of the porphyrin planar oscillators in slipped face-to-face stacking.

Interfacial Adsorption State of Protonated Lipophilic Porphyrins in a Liquid-Liquid System by Using Reflection Spectrometry

“…Sharp and intense absorption bands at 473 nm could arise from the dipole moment polarized along the long axis with the aid of an interporphyrin charge resonance in the excited states, whereas a broad absorption band at 412 nm could arise from the moment along the short axis. 13,17 Therefore, split bands at 477 and 466 nm observed in the present system indicate the coexistence of two kinds of Jaggregates (J1 and J2) with a polymorphous relation.…”

Disorder-induced exciton localization and violation of optical selection rules in supramolecular nanotubes

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] Examples of molecules that in solution self-assemble into aggregates of a tubular shape are carbocyanine molecules with hydrophobic and hydrophilic side groups [2][3][4][5][6][7] and porphyrin derivatives. [8][9][10][11][12] Both these molecules yield aggregates with a diameter of the order of 10 nm and a length of up to microns, which explains why they are often referred to as molecular nanotubes. Their shape and size resemble natural light-harvesting systems in green sulphur bacteria, 1,[13][14][15][16][17][18] while these systems also have a comparable geometry to previously studied helical polymers.…”

Stirring competes with chemical induction in chiral selection of soft matter aggregates

“…More striking is the report that the combination of soft aggregation and stirring may lead not only to chiral induction 22,23 but, more importantly, also to sign selection, in both three 24,25 and two dimensions 26,27 . Discussions on the true nature of such an enantioselection in three-dimensional aggregates have raised some controversy [28][29][30][31][32][33] . Recently, d'Urso et al 34 have hinted at the possibility to exert enantioselective control on the supramolecular assembly of achiral components doped with a chiral complex by means of vortex flow.…”