The deactivation process of J-aggregates of DDEOCI (3,3'-diethyl-5,5'-diphenyl-9-ethyl-oxacarbocyanine iodide) was investigated by means of steady-state and time-resolved absorption and fluorescence spectroscopy. The decay kinetics as well as the transient absorption spectra have been analyzed including different aggregate structures and exciton-exciton annihilation.

Results are presented of time resolved fluorescence and absorption investigations of DDEOCI (3,3'-diethyl-6,6'-diphenyl-9-ethyl-oxacarbocyanine iodide) in solvents which differ in polarity and viscosity. The measured picosecond absorption and fluorescence kinetics probed at various wavelengths of the polymethine dye studied can be fitted to a double exponential decay with a minor fast component of lifetime τ1 and a major slower component of lifetime τ2. Furthermore, probing in the S1←S0 absorption region and in the fluorescence region results in a residual with a lifetime of some ns and belonging to the detected red-shifted photoisomer with a low quantum yield (φ < 10%). The lifetime and the preexponential factors of the two components are in methanolic solution uneffected by changes of the anion.The detected two picosecond lifetime components are supposed to belong to two isomeric species (all-trans and mono-cis isomer) with strongly overlapping absorption spectra.

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Abstract— Using the example of Zn‐octaethylporphin π‐monoanion solution in tetrahydrofuran, we studied the dynamics of ultrafast photoprocesses in porphyrin π‐anions using a tunable picosecond absorption spectrometer. The deactivation kinetics of the lowest excited electronic (doublet) state of Zn‐octaethylporphin iT‐monoanion has been determined and was found to be followed by a single exponential function with the characteristic time 135 ps. It is shown that upon picosecond excitation to the long wavelength absorption band (λmax= 830 nm) the process of two‐quantum photoionization of the involved monoanion is easily realized, with the results that the observable kinetics of spectral changes exhibit a strong dependence on the excitation intensity.