Red-edge and inhomogeneous broadening effects of the electronic spectra of ethyl 5-(4-aminophenyl)-3-amino-2,4-dicyanobenzoate

Fluorescence excitation, fluorescence and phosphorescence spectra of ethyl 5-(4-aminophenyl)-3-amino-2,4-dicyanobenzoate (EAADCy) were recorded in tetrahydrofuran (THF) at room (293 K) and low-temperature (77 K). In our previous publication [M. Józefowicz, M. Aleksiejew, J.R. Heldt, A. Bajorek, J. Pączkowski, J. Heldt, Chem. Phys. 338 (2007) 53], it was shown that at room temperature, the fluorescence spectrum of EAADCy in THF consists of two bands. The short-wavelength emission corresponds to the molecular conformation in which the donor and acceptor moieties are orthogonal to each other, on the other hand, the long-wavelength emission is assumed to originate from a singlet excited state of molecule in which two moieties are coplanar. In present communication, the fluorescence and phosphorescence behavior of the EAADCy has been studied as a function of the excitation wavelength. The luminescence spectra of the molecule under study in THF glass at 77 K show considerable dependence on the excitation wavelengths. Such dependence of the wavelength of maximum intensity of luminescence (fluorescence and phosphorescence) spectrum and the full width at half maximum of phosphorescence spectrum (Δν˜1/2ph) on the excitation wavelength is a characteristic demonstration of the red-edge effect. These results along our previous studies [M. Józefowicz, M. Aleksiejew, J.R. Heldt, A. Bajorek, J. Pączkowski, J. Heldt, Chem. Phys. 338 (2007) 53] indicate that EAADCy forms a typically spectrally inhomogeneous system.