Synthesis, characterization, and photophysical properties of cyclotriphosphazenes containing quinoline-4-aldehyde-p-oxyanil moieties

Abstract

In the present work, a series of cyclotriphosphazenes including Schiff bases, {[N₃P₃(biph)₂(R)₂] (5), [N₃P₃(biph)(R)₄] (6), and N₃P₃R₆ (7) (biph = 2′,2′′-dioxy-1′,1′′- biphenyl, R = Quinoline-4-aldehyde-p-oxyanil}, were synthesized in high yields via the nucleophilic substitution reactions of quinoline-4-aldehyde-p-hydroxyanil (1) with [N₃P₃(biph)₂Cl₂] (2) and [N₃P₃(biph)Cl₄] (3) and N₃P₃Cl₆ (4), respectively. The structures of all products (5, 6, and 7) were defined by elemental analysis, mass spectrometry, FTIR, (¹H, ¹³C, and ³¹P) NMR spectroscopies. Furthermore, the photophysical properties of these new cyclotriphosphazenes (5, 6, and 7) in different solvents and concentrations were investigated and the results were compared and discussed. The absorption characteristics of novel cyclotriphosphazene-based Schiff bases demonstrated n–π* and π–π* transitions which can be attributed to quinoline side whereas absorbance values were significantly enhanced under the same analytical conditions when the number of quinoline groups attached to the cyclotriphosphazene-core increased. As a result, the molar absorptivity of novel cyclotriphosphazene-based Schiff bases which substituted with two (5) and six quinolines moieties (7) were increased 4.43- and 11.4-fold, respectively, when compared with their precursor (1).

Graphical Abstract

Keywords:

• Cyclotriphosphazene
• phosphazene
• quinoline-4-aldehyde-p-hydroxyanil
• Schiff base
• photophysical properties