Spectroscopic properties of ethyl 5-(4-dimethylaminophenyl)-3-amino-2,4-dicyanobenzoate

Abstract

Dedicated to Professor Józef Heldt on the occasion of his 75th birthday Keywords:Ethyl 5-(4-dimethylaminophenyl)-3-amino-2,4-dicyanobenzoate Charge transfer fluorescence Donor-acceptor system a b s t r a c tWe report the synthesis and photophysical properties of ethyl 5-(4-dimethylaminophenyl)-3-amino-2,4-dicyanobenzoate (EDMAADCy) in neat solvents of different polarity. The relation between molecular conformations of molecule under study and spectral behavior has been studied using steady-state spectroscopic technique, electrochemical measurements, and quantum-chemical calculations. The fluorescence spectra of EDMAADCy possess, in medium polar solvents, two bands. Theoretical studies of the TICT phenomenon have been made in order to explain the dual emission of the molecule under study. Calculated electric dipole moments in the ground and excited states, for perpendicular and flatted conformers, have been compared with experimentally determined data. Additionally, the results of spectroscopic measurements were used to calculate, according to Marcus theory, the outer-sphere solvent reorganization energy and the internal molecular reorganization energy.

Excitation-wavelength Dependent Fluorescence of Ethyl 5-(4-aminophenyl)-3-amino-2,4-dicyanobenzoate

“…We found that for EAADCy molecule the ground-state rotational potential is essentially flat (in the range from 60° to 120°) [18, 19]. Figure 1a shows the calculated ground-state ( S 0 ) rotational potential and the corresponding rotamer distribution function n ( φ ) determined from Boltzmann’s low at 298 K, for the molecule under study.…”

“…To test whether the changes in the absorption, fluorescence excitation and fluorescence spectra originate from the solute conformers possesing different angles between their interatomic planes of the donor and acceptor moieties, a series of conformational semiempirical quantum mechanical calculations were carried out. We found that for EAADCy molecule the ground-state rotational potential is essentially flat (in the range from 60° to 120°) [ 18 , 19 ]. Figure 1a shows the calculated ground-state ( S 0 ) rotational potential and the corresponding rotamer distribution function n ( φ ) determined from Boltzmann’s low at 298 K, for the molecule under study.…”

“…As it was mentioned earlier, the range of inhomogeneous broadening depends on the values of dipole moments of the dye molecules in the ground and excited states. From the quantum-chemical calculations [ 18 , 19 ] (see Fig. 1b ) it is evident that dipole moment of EAADCy in the ground state shows a very week dependence on the dihedral angle, whereas in the first excited state planar molecule possesses five times greater dipole moment than that with perpendicular donor-acceptor arrangement (i.e., 15.6 D versus 3.0 D).…”

Excited-State Dynamics of Ethyl 5-(4-aminophenyl)-3-amino-2,4-dicyanobenzoate

“…As it was mentioned, we have recently undertaken spectroscopic studies of the ICT properties of EAADCy. It has been shown in our previous papers that the photophysical properties of EAADCy are very sensitive to the microenvironment. − On the basis of the experimental results and quantum-chemical calculations, it has been shown that the fluorescence spectra of EAADCy in medium polar solvents consist of two bands at room temperature. The short-wavelength (SW) band corresponds to the emission from the locally excited state (mainly emission of the excited acceptor moiety).…”

“…Taking into account the results of our previous publications, − this study focuses on the improved and complete knowledge of the charge transfer process in EAADCy. In order to clarify the excited-state dynamics of EAADCy, which would greatly facilitate its application in NLO material studies, we have carried out a series of femtosecond transient absorption and time-resolved nanosecond fluorescence measurements of the title compound in solvents of varying polarity and viscosity.…”