Apparatus for Ultrafast Time-resolved Fluorescence and Intramolecular Charge Transfer Dynamics at Cryogenic Temperature

Abstract

Development of ultrashort laser has realized experimental observation of the elementary chemical processes such as intramolecular charge transfer (ICT), solvation dynamics, and energy transfer. These processes are triggered by photoexcitation and occur within hundreds of femtoseconds. Time-resolved fluorescence (TF) for molecular system at cryogenic temperature is often a successful approach to study excited state dynamics because spontaneous fluorescence is derived from excited states exclusively. In addition, thermally activated motions or reactions are suppressed at cryogenic temperature, allowing the system to be selectively studied.

In this thesis, development of apparatus for TF at cryogenic temperature is reported. It is shown that the apparatus successfully cooled the sample down to 10 K and reproduced 45 fs time resolution similar to the resolution achieved at room temperature. Utilizing the developed apparatus, the whole ICT dynamics of prodan molecule is investigated. Since dynamic Stokes shift is negligible below the melting point, TF spectra of prodan in 1-propanol at 190 K directly confirmed the emission from locally excited and charge transfer species. New properties of matter can be observed at low temperature. Crystalline acetonitrile is found to be favorable for excess ICT reaction. Several coumarin molecules in acetonitrile were prepared and they showed a broad fluorescence only at alpha phase temperature. At the end of the thesis, an application study on energy transfer within perylenediimide (PDI) tetramer molecules is investigated.