- Hydrogen bonded dimers of ketocoumarin in the solid state and alcohol:water binary solvent: Fluorescence spectroscopy, crystal structure and DFT investigation
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The photophysical properties of 3,3′-carbonylbis(7-diethylamino)-2H-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 of KC 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 between KC molecules in the alcohol:water binary mixture. The XRD structure reveals the two modes of intermolecular CH?OC hydrogen bonding (HB) which lead to two dimeric forms of KC, D1 and D2. The emission wavelength dependent excitation spectrum in the solid state and alcohol:water binary mixture confirms the H-type nature of dimer D1 and the J-type nature of dimer D2. The time-resolved fluorescence studies indicate that the new decay component with a lifetime of 2.71 ns is due to dimer D1 and the new emission with the maximum at 550 nm is due to dimer D2. Density functional theory (DFT) analysis confirms that the KC dimers are stabilized by hydrogen bonding and other non-covalent interactions. The hydrogen bonded KC dimers are responsible for the anomalous fluorescence behavior of KC in the alcohol:water binary mixture and for the bright yellow fluorescence in the solid state.
- Ramamurthy, Kannan,Malar, E. J. Padma,Selvaraju, Chellappan
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- Synthesis, spectroscopic properties, and DFT correlative studies of 3,3′- carbonyl biscoumarin derivatives
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A facile and simple method for the synthesis of a library of 3,3′- Carbonyl biscoumarin derivatives via a one-pot chemical reaction is reported. The synthesized fluorescent dyes were purified and characterized by analytical methods. The IR, 1H-NMR, and MS results confirmed the corresponding structure of the fluorescent dyes. The absorption and fluorescence spectra of fluorescent dyes were recorded in different solvents of varying polarity to understand the solvatochromic behaviour and dipole moments. Stoke's shift exhibits a redshift with an increase in solvent polarity for all molecules indicating a π→π? transition. The ground state dipole moments of all fluorescent dyes are estimated theoretically from ab initio computations (integral equation formalism of polarizable continuum model) and experimentally from the solvatochromic method and the results are compared. Further, using solvatochromic correlations like Lippert's, Bakhshiev's, Kawski-Chamma-Viallet's, and solvent polarity parameter the excited state dipole moments are determined. Results show that the excited state dipole moments are higher than the ground state dipole moments which suggests that, all fluorescent dyes are more polar in the excited state. The HOMO-LUMO energy gaps computed from density functional theory and absorption threshold wavelengths are found to be in good agreement and also support intramolecular charge transfer (ICT). Using HOMO-LUMO energies, the chemical hardness (η) of the molecules is determined and the chemical stability is discussed. Further, using DFT molecular electrostatic potential (MESP) plots, the electrophilic site and nucleophilic site which are useful in photochemical reactions were identified. The preliminary observations and results suggest that the fluorescent dyes can be considered as potential candidates for fluorescent probes and construction of dye-sensitized solar cell in future
- Mahadevan, K. M.,Malimath, G. H.,Naik, Lohit,Naik, Soniya,Savanur, Hemantkumar,Sutar, Suraj M.,Walki, Shashikant
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- KETOCOUMARINS. A NEW CLASS OF TRIPLET SENSITIZERS
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Several derivatives of 3-ketocoumarins were prepared and are shown to have many of the photophysical criteria required for efficient triplet sensitizers.These compounds include 3-aroylcoumarins (1) and 3,3'-carbonyl-biscoumarins (2).The aryl groups in 1 are either phenyl and substituted phenyl derivatives or heterocyclic groups such as thienyl and benzofuryl.The substituents on the coumarin moiety in 1 and 2, if any, are alkoxy or dialkylamino.These compounds, with absorption maxima between 330 and 450 nm, have extinction coefficients in the range of 1E4 to almost 1E5, which is an important criterion for efficient sensitization of thin films of polymers as those used in photoresists and litography.The singlet-triplet intersystem crossing (isc) efficiencies of several derivatives approach unity.In others, however, a radiationless decay process competes with the isc.The decay process is particularly dominant in the assymetrically substituted derivatives of 2, but seems to be considerably supressed in polymeric matrices.The triplet energies of these compounds range from ca. 48 to 60 kcal/mol.Some of these ketocoumarins show phosphorescence spectra that suggest the presence of "frozen-in" rotamers.
- Specht, Donald P.,Martic, Peter A.,Farid, Samir,++
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p. 1203 - 1211
(2007/10/02)
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