Ultrafast hydrogen bond dynamics and partial electron transfer after photoexcitation of diethyl ester of 7-(diethylamino)-coumarin-3-phosphonic acid and its benzoxaphosphorin analog

Abstract

The solvation dynamics after optical excitation of two phosphono-substituted coumarin derivatives dissolved in various solutions are studied by fluorescence up-conversion spectroscopy and quantum chemical simulations. The Kamlet-Taft analysis of the conventional absorption and emission spectra suggests weakening of the solvent-solute H-bonds upon optical excitation, which is in contrast to the results gained by the quantum simulations and earlier studies reported for coumarin derivatives without phosphono groups. The simulations give evidence that the solvent reorganisation around the excited fluorophore leads to partial electron transfer to the first solvation shell. The process occurs on a timescale between 1 and 10 ps depending on the solvent polarity and leads to a fast decay of the time-resolved emission signal. Using the ultrafast spectral shift of the time-dependent fluorescence we estimated the relaxation time of the H-bonds in the electronically excited state to be about 0.6 ps in water, 1.5 ps in ethanol and 2.8 ps in formamide.

Individual control of singlet lifetime and triplet yield in halogen-substituted coumarin derivatives

“…Recent studies on p-conjugated systems reported a correlation between uorescence QY and extension in the conjugated p-system. 47,48 Moreover, intramolecular chargetransfer processes, which are common in coumarins, 22,49,50 lead to large changes in dipole moment between ground and excited state accompanied by a signicant increase of the uorescence intensity. 47,50 Accordingly, the rise of Dm from 2.0 D to 4.12 D and 4.65 D going form 6-H to 6-Cl and 6-Br, respectively, suggests an increase of the uorescence QY in the same way.…”

“…20,21 In other approaches the comparably small coumarin moiety was used to study the attached functional groups. [22][23][24] In our case the 3-substituted diethylphosphono and phosphono groups are commonly known for their enzyme inhibiting abilities. 25,26 The electron withdrawing effect of the diethylphosphono group on the conjugated aromatic coumarin structure reduces the electron density stronger on 7 with respect to 6-position.…”

“…Moreover, the same functional was successfully applied to study the intramolecular charge transfer in coumarin molecules 39,40 and also a charge transfer from coumarin to the solvent molecules. 22 The solvent effects were considered with a polarizable continuum model (PCM). 41 In PCM formalism the solvent is described as a homogeneous dielectric medium, which is polarized by the solute.…”

Efficient Synthesis of Fluorescent Coumarins and Phosphorous-Containing Coumarin-Type Heterocycles via Palladium Catalyzed Cross-Coupling Reactions

“…The absorption and emission spectra of several compounds ( CM-1—CM-12 , Table 1 ), varying the substituent in position C-6 of the coumarin ring were calculated. Based on previous investigations in our group, coumarins bearing substituents in position C-6 [ 33 ] and C-7 [ 34 ] exhibit good fluorescent properties. The model compounds phenyl and aryl groups were chosen to enlarge the conjugated system, connected to the coumarin fragment.…”