J.S., A.W., H.K. Free Univ. of Berlin, Takustr. 3, 14195 Berlin, Germany
J.E., R.E. BiosQuant GmbH Berlin, Rudower Chaussee 6, 12489 Berlin, Germany
ps-Lifetimes studies of the fluorescence decay of porphyrin-triptycene-quinones as typical model systems for electron transfer (ET) studies have been performed. These dyes were chosen on the basis of their rigid structure, high ET rates and their advantageous absorption properties. The extremely short monoexponential lifetimes of the dyes favor their use as standards in ps-lifetime measurements. The short lifetimes are caused by an intramolecular ET process. A prerequisite for such an application are highly purified substances, due to their very low fluorescence quantum yields. Depending on the meso-substitution and complexation of the porphyrin, as well as the reduction potential of the quinone, different lifetimes in the range of 1 to 85 ps are obtained. The measurements were made on an ultrafast TCSPC system based on a frequency doubled TiSa laser, subtractive double monochromator and a MCP-PMT detector. The instrumental response function (IRF) of the system is less than 20 ps, allowing the determination of decay times of less than 5 ps using deconvolution techniques. Interpretation of data requires an adequate IRF or a standard fluorescence function at the same wavelength as the sample fluoresces. This function should have a well defined monoexponential decay as basis for correct deconvolution results. This is of importance especially for the investigation of dyes with ultrafast decay of the excited state, large Stokes shifts or an excitation to higher excited states. The application of porphyrin-quinones as standards for these measurements is described.
Examples:
Poster presented on the SPIE conference in San Jose, California USA, 4.-10. February 1995.
For more information contact the above addresses or via e-mail:
sobek@chemie.fu-berlin.de
wiehe@chemie.fu-berlin.de
j.enderlein@tbx.berlinet.in-berlin.de