Synthesis and fluorescence studies of nine 1,5-benzodiazepine-2,4-dione derivatives: Dual emission and excimer fluorescence
The photophysical properties of nine 1,5-benzodiazepine-2,4-dione (BZD) derivatives were investigated using absorption and fluorescence spectral techniques in dimethyl sulfoxide. The trend of red shifts caused by the substitutions had full compliance with the trend of decreasing the calculated band gap (ΔE LUMO-HOMO ) by semi-empirical AM1 and DFT/B3LYP/6-311+G* computational methods. The positive solvatochromism of BZD a demonstrated the π-π* nature of the singlet excited state. Dual fluorescence was observed in the emission spectra of BZD f and g, while their spectrum in different concentration showed only one peak short wavelength (SW) in dilute solutions. The main peak in SW around 370nm was attributed to the monomer of BZD (f* or g*) and the broader emission shifted to the visible region around 400nm in middle wavelength (MW) to the intermolecular excimer emission of BZD ([f/f]*or [g/g]*). The observed phenomena, such as solvatochromism, dual fluorescence, some red shifts caused by substitution, and larger Stokes shift indicated the existence of intramolecular charge transfer (ICT) in the BZDs series. The phosphorescence emission of the BZDs demonstrated their intersystem crossing (ISC) process.
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