NDLI: Excited state evolution in polydiacetylene studied by sub-10-fs time resolved spectroscopy

Content Provider	IEEE Xplore Digital Library
Author	Cerullo, G. Lanzani, G. Zavelani-Rossi, M. De Silvestri, S. Comoretto, D. Moggio, I. Dellepiane, G.
Copyright Year	2000
Description	Author affiliation: Dipt. di Fisica, Politecnico di Milano, Italy (Cerullo, G.; Lanzani, G.; Zavelani-Rossi, M.; De Silvestri, S.)
Abstract	Polydiacetylenes are a well-known class of one-dimensional /spl pi/-conjugated semiconducting polymers. They display optical transitions with high oscillator strength and low photoluminescence efficiency (typically 10/sup -4/). This is consistent with ultrafast relaxation of the primary photoexcited state 1/sup 1/B/sub u/ into one or more dark states, i.e. states which are energetically below the 1/sup 1/B/sub u/ state and not optically coupled to the ground state. The recent availability of sub-10-fs pulses in the visible range enables direct monitoring of this process. In this work we study solutions of polycarbazolyldiacetylene in benzene, which show a steep onset of ground state absorption. The differential transmission signal is shown as a function of pump-probe delay at the probe wavelength of 590 nm. Because of the negligible ground state absorption at this wavelength, the increased transmission is assigned to stimulated emission from the photoexcited 1/sup 1/B/sub u/ state. The decay of the emission corresponds to the quick internal conversion to the lower energy, optically dark 2/sup 1/A/sub g/ state. The same dynamics are observed over the whole stimulated emission region. Superimposed on the transient signal we observe coherent molecular oscillations. The lack of oscillations different from those identified in the Raman spectrum suggests that ground state vibrations are probed. The absence of excited state modes can be explained by the short lifetime of the excited 1/sup 1/B/sub u/ state, which is rapidly depopulated towards the dark state.
File Size	94448
File Format	PDF
ISBN	0780363183
DOI	10.1109/IQEC.2000.908202
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2000-09-10
Publisher Place	France
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Spectroscopy Stationary state Optical pumping Ultrafast optics Stimulated emission Dark states Semiconductivity Displays Optical polymers Oscillators
Content Type	Text
Resource Type	Article

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