Unusual emissions from low-concentrated porphyrin solutions.
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.
Jellen
Claus-Peter
CP
Institute of Physical Chemistry, Heinrich-Heine-University of Düsseldorf, Universitatsstr 1, D-40225, Düsseldorf, Germany.
Bettermann
Hans
H
D000096:Acetone; D011166:Porphyrins / Q000737:chemistry*; D012996:Solutions; D012997:Solvents; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry; D014867:Water
D011166:Porphyrins; D012996:Solutions; D012997:Solvents; D014867:Water; D000096:Acetone