32387-94-3Relevant academic research and scientific papers
Spectral-luminescent properties of 2,3-diphenyl-6-X-quinoxalines
Rtishchev,Dobrodei,El'tsov
, p. 1658 - 1668 (2007/10/03)
A study is made of the spectral-luminescent properties of solutions of 2- and 6-phenylquinoxalines and 2,3-diphenyl-6-X-quinoxalines (X = H, CH3, OC2H5, NH2, C6H5, C6H5O, C6H5CHOH, I, Br, Cl) in a hydrocarbon and 95% ethanol at 295 and 77 K. The energies of the S1 and T1 states obtained (25 600-27 700 and 18 500-20 000 cm-1, respectively) are correlated to the nature of the substituents. The mixed character of the luminescence is inferred from the close location of the S(ππ*) and S(nπ*) levels for the majority of the compounds. The contribution from the ππ* component increases with increasing electron-donating power of the substituent, as well as in going from nonpolar to polar solvent. The quantum yields of fluorescence φ = 10-4-1.1 × 10-1, of the intercombination transition φST = 0.3-0.9, and of phosphorescence φph = 0.2-0.9, the phosphorescence lifetime (τph = 10-3-0.57 s), as well as the established phenomenon of phosphorescence of liquid solutions, are analyzed in the framework of the vibronic and spin-orbit coupling schemes and conformational changes caused by excitation. The difference in the luminescent properties of 2,3-diphenyl-6-aminoquinoxalines from its examined analogs is due to a low energy of the S1(ππ*) level (21 200 cm-1 in alcohol), which is responsible for intense fluorescence (φf -0.5 in alcohol) and very weak phosphorescence.
