Solvatochromic, spectroscopic and DFT studies of a novel synthesized dye: l-(4-Dimethylaminophenyl)-2-(5H-phenanthridine-6-ylidene)-ethanone (6-KMPT)

A novel solvatochromic l-(4-dimethylaminophenyl)-2-(5H-phenanthridine-6-ylidene)-ethanone (6-KMPT) dye was synthesized and characterized by means of NMR, IR, mass spectroscopies. Also, it was studied using UV-vis and fluorescence spectroscopic methods in a broad range of solvents. UV-vis results showed that increasing 6-KMPT concentration dose not cause molecular aggregation in chloroform. Varying the temperature in the range from 25 to 55 °C dose not have a significant effect on the characteristics bands of the molecule. However, in the presence of surfactant SDS the UV-vis spectrum undergoes drastic alteration. This phenomenon is related to the removal of hydrogen atom from nitrogen atom of phenanthridine moiety. Fluorescence spectroscopic results showed that 6-KMPT has an appreciable fluorescence quantum yield. The effect of excitation wavelength, concentration of 6-KMPT, concentration of oxygen and surfactants (SDS, C16TAB, CPC, Brij-35) were studied. Further results showed that the fluorescent behavior of 6-KMPT can be attributed to planarity induced by intramolecular hydrogen bonding which can in turn be destroyed by anionic surfactant SDS. Results showed that oxygen and SDS can be operate as fluorescence quencher compounds for 6-KMPT and Stern-Volmer plot showed a straight line. Fluorescence polarization and anisotropy of 6-KMPT in chloroform strongly depend on concentration. The 6-KMPT exhibits solvent-induced spectral band shifts. By using Lippert equation, the change of dipole moment of 6-KMPT molecule upon excitation was estimated as 6.39 D. Furthermore, absorption, fluorescence emission, Stokes shift values and fluorescence quantum yield (ΦF) of 6-KMPT in different solvents of polarity were determined. Maximum ΦF value of 0.372 for 6-KMPT molecule was found in ethanol solvent with a Stokes shift of 2446.8 cm−1. The results of DFT calculations showed that tautomer 2c (enol) energetically is more stable than tautomer 2b (keto) in gas phase whereas it was vice versa in CHCl3.