In this paper we report on the synthesis and photophysical properties of the energy-transfer system 2 a, in which a quinquethiophene bridge is terminally linked to the 5-position of a porphyrin and to the 9-position of an anthracene group. The photoexcitedstate properties were studied by steady-state fluorescence and picosecond time-resolved fluorescence measurements as well as fluorescence excitation spectroscopy. The weak electronic interaction of the subunits anthracene, quinquethiophene and porphyrin results in localized excited states, which are seen in UV/Vis absorption spectra. In 2 a, a highly selective excitation of the anthracene donor leads to quantitative intramolecular energy transfer to the emitting porphyrin acceptor via the quinquethiophene bridge. The efficiency of energy transfer and the fluorescence properties are both independent of the length of the oligothiophene chain, as demonstrated by comparison with the model compounds 1. Various explanations for the mechanism of intramolecular energy transfer are discussed. Introduction of additional anthrylquinquethienyl units into the porphyrin ring results in an increase in the intensity of the characteristic absorption bands and fluorescence nearly proportional to the number of chromophores.

No abstract

Using a combination of a fast two-dimensional-Hartree-Fock-Roothaan method and highly accurate fixed-phase diffusion quantum Monte Carlo simulations, we analyze the electronic structure and calculate the energy of the ground states of atoms with nuclear charges Z = 2-26 in very strong magnetic fields B = 10 7 -5 × 10 8 T, relevant for astrophysical problems, e.g., the thermal emission of strongly magnetized isolated neutron stars.

9-Anthryl-oligothiophenes (9A-T., n= l-4) have been studied in n-hexane solution between helium and room temperature using absorption, fluorescence emission and excitation spectra and time resolved fluorescence measurements. These compounds are reference systems for studies on intramolecular energy and charge transfer in donor/acceptor-substituted conjugated chain molecules. The absorption spectra show contributions of both substituents anthracene and oligothiophene, but no additional bands due to mixed electronic states. Dual fluorescence is observed at T, 120 K for the compounds 9A-T, (n= l-3), but not for 9A-T+ Time resolved spectroscopy reveals a dynamical coupling between the two emission components whose relative quantum yields are strongly temperature dependent. The occurrence of the dual fluorescence is explained by an intramolecular torsional motion between the two molecular subunits.

No abstract