Zusammenfassung
The fluorescence behaviour of tetraphenylporphyrin appended cellulose strands in chloroform is studied by weak cw excitation and intense picosecond laser pulse excitation (wavelength lambda(L) = 347.15 nm, duration Deltat(L) = 35 ps). With rising pump pulse energy density, a reduction of the fluorescence efficiency and a shortening of the fluorescence signal decay time are observed. The energy ...
Zusammenfassung
The fluorescence behaviour of tetraphenylporphyrin appended cellulose strands in chloroform is studied by weak cw excitation and intense picosecond laser pulse excitation (wavelength lambda(L) = 347.15 nm, duration Deltat(L) = 35 ps). With rising pump pulse energy density, a reduction of the fluorescence efficiency and a shortening of the fluorescence signal decay time are observed. The energy density dependent fluorescence quenching is analysed in terms of intra-strand singlet exciton-singlet exciton annihilation. The annihilation constant is determined and a critical singlet exciton number density (N-ex,N-ann = 4.8 x 10(19) cm(-3)) as well as a critical fraction of excited repeat units (f(RU,ann) = 0.1) for annihilation are determined. Additionally the excited-state absorption cross-section, sigma(ex,L), at the pump laser wavelength, lambda(L), is determined by energy density dependent transmission measurements and is found to be approximately equal to the ground-state absorption, sigma(L), at lambda(L). The small-signal fluorescence quantum distribution, fluorescence quantum yield (phi(F) = 0.072), and degree of fluorescence polarisation (P-F = 0.04) are determined by cw fluorimetry. The emitting exciton size is found to be equal to the repeat-unit size of the cellulose strands. (C) 2002 Elsevier Science B.V. All rights reserved.
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