J- and H-Aggregates of Porphyrin−Surfactant Complexes:  Time-Resolved Fluorescence and Other Spectroscopic Studies

Abstract

The interactions of several water-soluble ionic porphyrins with different ionic or neutral surfactants in aqueous solutions were studied as a function of surfactant concentration. The interaction leads to the formation of porphyrin aggregates and/or micelle-encapsulated monomers with the exception of those porphyrin−surfactant pairs for which the interaction is Coulombically repulsive. The premicellar surfactant−porphyrin aggregate is identified by absorption and fluorescence spectroscopy, fluorescence lifetime and anisotropy, and resonance light scattering. The spectroscopic results are used to characterize the premicellar aggregates as J-type, H-type, or nonspecific aggregates. All premicellar surfactant−porphyrin aggregates dissociate to form micelle-encapsulated monomers when the surfactant concentration approaches cmc (critical micellar concentration). The interaction of tetrakis-(4-sulfanatophenyl)porphine dianion (H4TPPS2-) at pH <3.5 with cetyltrimethylammonium cation (CTAB) is described by the following sequential equlibria controlled by the surfactant concentration: M ⇌ J ⇌ H ⇌ Mm. The stoichiometric ratio of porphyrin/surfactant is 1:2 for the J-aggregate and ∼1:4 for the H-aggregate. Kinetic intermediates were also observed prior to the formation of the J-aggregate. The J-aggregate exhibits circular dichroism (spontaneous chirality, not seen in H-type or micellar aggregates), intense resonance light scattering, low fluorescence quantum yield and lifetime, and unusually high fluorescence anisotropy.

Dye aggregation and influence of pre-micelles on heterogeneous catalysis: A photophysical approach

“…The dimer formation is characterized by a large spectral change in the absorption spectrum around the main absorption peak in the visible spectrum (absorption decreases and a blue shifted shoulder appears), which characterizes the aggregation of dyes [6]. Relative to the dimerization, it is established that H (sandwich aggregates) and J (head-to-tail aggregates) [7] are possible conformation of dimers [8]. H-aggregates promotes hypsochromic shift in the absorption spectrum, representing weakly fluorescent species while the J-aggregates are fluorescent and provokes bathochromic shift [8].…”

Translational and Rotational Motions of Albumin Sensed by a Non-Covalent Associated Porphyrin Under Physiological and Acidic Conditions: A Fluorescence Correlation Spectroscopy and Time Resolved Anisotropy Study

“…Moreover, under acidic conditions TSPP is prevalently present in solution as a zwitterion. This has proved to contribute decisively to the formation of highly ordered molecular aggregates of the porphyrin at relatively low [TSPP] induced by different polymeric templates [12][13][14] including albumins [11,15]. These aggregates of J-type are particularly interesting in view of their possible applications in nonlinear optics, nanometer-sized photoconductors, and light harvesting systems and contributed also for the relevance of the studies carried on at pH=2.…”

Triplet Thermal Relaxation Study as a Probe of Weak Interdimers of Porphyrin Derivatives

“…The increasing intensity is also observed in the absorption range of 606/607 nm. All these changes in the absorption (even the small ones) would suggest creation of some aggregates of dyes 1 and 2 [16,17,19,51]. The appearance of the bands at 703 nm could rather be assigned to the vibrational mode of the alkyl chains covalently linked to the indole units which vanish when aggregates are created (in the highly concentrated samples); in the metalfree non-substituted phthalocyanines, this band is not observed [25].…”

“…τ 1 ≤ 0.4 µs TD = ± 0.1, α = ±0.06, K 1 , K 2 = ±0.01, Φ T = ±0.10, τ 2 = 0.01 µs to 0.03 µs samples. According to [16,17], the decay time shorten by the N factor (N -number of monomers which constitute aggregates). For samples 1 and 2 the numbers could be 2 and 4, respectively.…”

“…In the ideal J aggregate, the polarization axis of the electronic transition is directed along the line of the molecular centers. In a double molecule with the coplanar transition dipoles inclined to the interconnected axis, an angle between the dipole moment's directions ranges from 54.7 • to 90 • and 0 • to 54.7 • in H and J, respectively [16][17][18][19]. The blue and red absorption shifts are expected to appear in the absorption spectrum of the H and J aggregates, respectively [2,20].…”