Asymmetric indolylmaleimide derivatives and their complexation with zinc(II)-cyclen

B.K. Kaletas, H.C. Joshi, G. van der Zwan, M. Fanti, F. Zerbetto, K. Goubitz, L. De Cola, B. Konig, R.M. Williams

Research output: Contribution to JournalArticleAcademicpeer-review


The spectroscopic properties of two asymmetric indolylmaleimide derivatives, 4-bromo-3-(1′H-indol-3′-yl)-maleimide and 4-memyl-3-(1′H-indol-3′-yl)maleimide, are investigated. The bromo derivative was crystallized and its X-ray structure was determined. Both compounds are strongly colored while their separate components (indole and maleimide) absorb in the UV region only. To understand the ground- and excited-state behavior, the photophysical properties of the two compounds were studied in detail by steady state and time-resolved absorption and emission spectroscopy. Their solvatochromic behavior was investigated by using the Kamlet-Taft approach, which indicates some charge transfer (CT) character in the excited state. Nano- and femtosecond transient absorption spectroscopy was used for the identification and investigation of the CT state. Furthermore, the effect of the complexation with zinc(II) 1,4,7,11-tetraazacyclododecane (Zn-cyclen) on the photophysical properties of these two compounds was studied. An enhancement of the fluorescence intensity upon self-assembly (up to 90 times) and high association constants were observed, which illustrate the potential use of these compounds as luminescent sensors. DFT calculations indicate that HOMO-1 to LUMO excitation is mainly responsible for the charge transfer character and that this transition changes its character drastically when Zn-cyclen complexation occurs, thus giving it sensor properties. © 2005 American Chemical Society.
Original languageEnglish
Pages (from-to)9443-55
JournalJournal of Physical Chemistry A
Issue number42
Publication statusPublished - 2005


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