Unusual emissions from low-concentrated porphyrin solutions |
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Authors: | Jellen Claus-Peter Bettermann Hans |
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Affiliation: | Institute of Physical Chemistry, Heinrich-Heine-University of Düsseldorf, Universitatsstr 1, D-40225, Düsseldorf, Germany. |
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Abstract: | This contribution presents fluorescence measurements from highly diluted tetratolylporphyrin (TTP) solutions where acetone has been chosen as solvent. The concentrations of the solutions ranged from 10(-8) to 10(-14) M. Apart the normal S1-S0 fluorescence a new broad emission was recorded below 10(-8) M. This new emission blue-shifted to the S1-S0 fluorescence covered the spectral range between 19000 and 14000 cm(-1). Within the dilution series, both the S1-S0 porphyrin fluorescence and the new emission exhibited a remarkably non-linear concentration-dependence. In the case in which the aggregate emission was strong, little S1-S0 emission could be detected and vice versa. The intensity maximum of the broad emission was detected from a 10(-13) M solution. The supplementary fluorescence was attributed to the presence of assembled molecules. This assumption was established by comparing the measurements with those obtained from 1:1 acetone water solvent mixtures in which the formation of aggregates had been formerly proven. The emission originating from the formation of aggregates was interpreted by a qualitative model considering the energy levels of J-aggregated porphyrins. |
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