Optical excitations of porphyrin J-aggregates

In this work, we will present a study of the optical properties of aggregated tetrakis(p-sulfonatophenyl)porphyrin (TSPP) in different environments which can have a dramatic influence on the spectroscopic features. We will show that when the porphyrins are free to self-organize (i.e. in saturated solutions) they show two distinct photoluminescence peaks, revealing the presence of two different species, with a relative population strongly dependent on the temperature. If aggregation occurs in an environment with restricted geometry (i.e. within the nanochannels of MCM-41) it is possible to modify the spontaneous self-assembly of the molecules and, as a consequence, the relative ratio of the two emissions intensity. We will report on the possibility to induce the preferential formation of the low-energy emitting species, aiming to tune in a controlled way the emission spectrum of the aggregate. (C) 2005 Elsevier B.V. All rights reserved.