Coherent internal conversion of pyrene revealed by pump-probe and ultrabroad 2D-UV spectroscopy

Pugliesi, Igor; Krebs, Nils und Riedle, Eberhard (Mai 2013): Coherent internal conversion of pyrene revealed by pump-probe and ultrabroad 2D-UV spectroscopy. 2013 Conference on Lasers & Electro-Optics Europe & International Quantum Electronics Conference CLEO EUROPE/IQEC, Munich, Germany, 12-16 May 2013. IEEE.

Abstract

Summary form only given. The 2D measurements on a light harvesting complex by Fleming and coworkers showed long lived oscillations [1] suggesting the existance of quantum-coherent effects in large macromolecules. In order to gain a deeper insight into these coherent phenomena, the intramolecular energy dissipation in restricted size molecules has to be investigated. Here we present a combined pump-probe and 2D-UV investigation of pyrene in solution, showing that in this molecule the coherent excitation of vibrational states survives the S 2 -S 1 internal conversion (figure 1a). The temporal evolution of the transient absorption of pyrene is shown in figure 1b. The S 2 excited state absorbtion band maximum at 575 nm reveals that the IC occurs with a time constant of 85 fs. The ultrafast decay of this band is accompanied by the rise of S 1 excited state absorpion bands in the range 340 - 380 nm and 450 - 525 nm. Both bands show oscillations that can be ascribed to wavepackets in the S 1 state indicative for coherent internal conversion. 2D-UV measurements on pyrene performed with our new collinear setup are shown in figure 2. As excitation we use UV pulses broadened by self-phase modulation to 25 nm to cover two vibronic bands of the S 2 1 B 2u S0 electronic transition of pyrene at 312 nm. An ultrabroad supercontinuum was used as probe. The observed S 1 excited state absorption between 340 - 380 nm (29400 - 26300 cm-1) displays an excitation dependent Franck-Condon envelope with an additional shoulder at 394 nm (25350 cm-1) only present at the high energy excitation side (figure 2b). The intensity of this shoulder does not increase steadily with increasing excitation energy, but displays a rather discrete step between the two excited vibronic bands. The 2D-UV and pump-probe measurements thus provide the complete experimental framework needed to identify the mechanism behind the coherent internal conversion on the vibrational level.

• Dokumententyp: Konferenzbeitrag (Paper)
• Fakultät: Physik
• Themengebiete: 500 Naturwissenschaften und Mathematik > 530 Physik
• Sprache: Englisch