Hydrogen bonded dimers of ketocoumarin in the solid state and alcohol:water binary solvent: fluorescence spectroscopy, crystal structure and DFT investigation. (28th May 2019)

• Record Type: Journal Article
• Authors: Ramamurthy, Kannan; Malar, E. J. Padma; Selvaraju, Chellappan
• Is Part Of: New journal of chemistry. Volume 43:Number 23(2019)
• Page Start: 9090
• Page End: 9105
• Publication Date: 2019-05-28
• Subjects: Chemistry -- Periodicals; Chimie -- Périodiques; 540
• DOI: 10.1039/c9nj01053j
• Languages: English
• ISSNs: 1144-0546

Abstract

Abstract : Fluorescence emission spectrum of ketocoumarin dimers in an alcohol:water binary mixture and the solid state. Abstract : The photophysical properties of 3, 3′-carbonylbis(7-diethylamino)-2 H -chromen-2-one (ketocoumarin) were investigated in the solid state, different solvents and an alcohol:water binary mixture using steady state, time-resolved fluorescence spectroscopy, XRD studies and DFT calculations. In neat solvents ketocoumarin (KC ) shows a small Stokes shift as compared to other 7-diethylaminocoumarin (7-DEC) dyes and this is due to the π–π* electronic transitions involving the bridge keto group. In aqueous alcoholic solution, the fluorescence maximum ofKC depends on the percentage of water and a new emission maximum at 550 nm with a large Stokes shift is observed at 90% water content. The solid state fluorescence and XRD crystal structure analysis reveals that the new decay component with a lifetime of 2.71 ns and new emission maximum in the alcohol:water mixture is due to the intermolecular hydrogen bonding [HB] interaction betweenKC molecules in the alcohol:water binary mixture. The XRD structure reveals the two modes of intermolecular CH⋯OC hydrogen bonding (HB) which lead to two dimeric forms ofKC, D1 andD2 . The emission wavelength dependent excitation spectrum in the solid state and alcohol:water binary mixture confirms the H-type nature of dimerD1 and the J-type nature of dimerD2 . The time-resolved fluorescence studies indicate that the new decay component with a lifetime of 2.71 ns is due to dimerD1 and the new emission with the maximum at 550 nm is due to dimerD2 . Density functional theory (DFT) analysis confirms that theKC dimers are stabilized by hydrogen bonding and other non-covalent interactions. The hydrogen bondedKC dimers are responsible for the anomalous fluorescence behavior ofKC in the alcohol:water binary mixture and for the bright yellow fluorescence in the solid state.