Photophysical kinetics in TICT-forming compounds - derivatives of DMABN

by Sukumaran, Murali

Abstract (Summary)
The focus of this work is mainly concerned with the investigation of photophysical properties of electron donor-acceptor compounds, namely, derivatives of N,N-dimethylamino benzonitrile (DMABN) and N-phenyl-pyrrolobenzonitrile (PBN). New insights into the intramolecular charge transfer (ICT) states were obtained while dealing with an acceptor moiety of increased strength in the form of fluorinated analogues of both these compounds. The molecules studied in this work have been compared with their corresponding parent compounds to get more useful information on the excited state behaviour. The spectroscopic and photophysical properties were studied using steady-state and time-resolved fluorescence at room and low temperature as well as with transient absorption spectroscopy in conjunction with quantum chemical calculations. Unlike in the parent compounds DMABN and PBN, their fluorinated derivatives show only a single strongly red-shifted fluorescence emitted from the ICT state, and possess low quantum yields. The nearly non-fluorescent behaviour for all of these fluorinated derivatives investigated is due to the presence of a photochemical mechanism additional to that of ICT, which acts as a new non-radiative funnel. The ICT observed in these compounds can be explained by twisting motion taking place between the donor and acceptor moieties. Thus, twisted intramolecular charge transfer (TICT) model supports the observations. Apart from the changes in the strength of the acceptor moieties, the ICT nature has been further explored by changing their linking positions as well as with additional acceptor substituents. From the findings obtained in this work, a deeper understanding of the charge separation processes occurring in donor-acceptor systems with high solvatochromism and non-radiative decay properties was obtained. The possibility for populating two different ICT states (of forbidden nature – TICT, and allowed nature – mesomeric ICT) has been exemplified.
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Bibliographical Information:


School:Humboldt-Universität zu Berlin

School Location:Germany

Source Type:Master's Thesis

Keywords:DMABN Charge transfer dual fluorescence TICT


Date of Publication:06/21/2005

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