Frankfurt 2006 – scientific programme

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MO: Molekülphysik

MO 42: Excitation and Coherence Decay

MO 42.4: Talk

Wednesday, March 15, 2006, 14:45–15:00, H12

Molecular mechanisms of fluorensence quenching of organic pigments — •Lisa Lorenz, Victor Matylitsky, Karsten Neumann, and Josef Wachtveitl — J.W. Goethe Universität, IPTC, Marie-Curie-Str. 11, 60439 Frankfurt/Main

The occurence of fluorescence of crystalline pigments is often explained by their intermolecular distance, which is thought to be the main parameter determining fluorescence quenching. In a recent study of the organic pigment P.Y.101 we found that in contradiction to common rules for solid state fluorescence, the radiationless deactivation of the excited state is a property of the individual molecule rather than a cooperative one.

In time resolved experiments on P.Y. 101 and three of its derivatives (one fluorescent and two non-fluorescent di-naphthyl-bisazomethin-based pigments), which are very similar in structure, we were able to show the dynamics and reaction pathways of deactivation. By embedding P.Y. 101 in a polyethylene matrix it was possible to compare dynamics in solution and in the microcrystalline state. It was found that the dynamics are slowed down by a factor of four in the solid state. For the non-fluorescent pigments a long-lived intermediate was observed which decayes via internal conversion.

These results are in excellent agreement with time-dependent DFT[1,2] studies of the excited state properties of P.Y. 101 and its derivatives.

1.) A. Dreuw et al. Angew. Chem. Int. Ed., 44, 7783, 2005

2.) J. Ploetner and A. Dreuw Solid-state fluorescence of Pigment Yellow 101 and derivatives: a conserved property of the individual molecules Phys. Chem. Chem. Phys., 2006, in press