title: Asymmetric indolylmaleimide derivatives and their complexation with zinc(II)-cyclen.
abstract: The spectroscopic properties of two asymmetric indolylmaleimide derivatives, 4-bromo-3-(1'H-indol-3'-yl)maleimide and 4-methyl-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.
authors.affiliation: Molecular Photonic Materials, van't Hoff Institute for Molecular Sciences, Universiteit van Amsterdam, Nieuwe Achtergracht 166, 1018 WS Amsterdam, The Netherlands.
authors.forename: Basak Kükrer
authors.initials: BK
authors.lastname: Kaletas
authors.forename: Hem C
authors.initials: HC
authors.lastname: Joshi
authors.forename: Gert
authors.initials: G
authors.lastname: van der Zwan
authors.forename: Marianna
authors.initials: M
authors.lastname: Fanti
authors.forename: Francesco
authors.initials: F
authors.lastname: Zerbetto
authors.forename: Kees
authors.initials: K
authors.lastname: Goubitz
authors.forename: Luisa
authors.initials: L
authors.lastname: De Cola
authors.forename: Burkhard
authors.initials: B
authors.lastname: König
authors.forename: René M
authors.initials: RM
authors.lastname: Williams
mesh_terms: D003198:Computer Simulation; D018360:Crystallography, X-Ray; D000080027:Cyclams; D006571:Heterocyclic Compounds / Q000737:chemistry*; D007211:Indoles / Q000737:chemistry*; D008301:Maleimides / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011789:Quantum Theory; D012680:Sensitivity and Specificity; D013056:Spectrophotometry, Ultraviolet / Q000379:methods; D013997:Time Factors; D015032:Zinc / Q000737:chemistry*
chemical_list: C521320:4-bromo-3-(1'H-indol-3'-yl)maleimide; C521319:4-methyl-3-(1'H-indol-3'-yl)maleimide; D000080027:Cyclams; D006571:Heterocyclic Compounds; D007211:Indoles; D008301:Maleimides; D009942:Organometallic Compounds; C038072:cyclen; D015032:Zinc