Synthesis and characterization of new poly(aryl ether)s with isolated fluorophores

Four novel poly(aryl ether)s (P1-P4) consisting of alternate isolated electron-transporting (3,3‴-bis-trifluoromethyl-p-quaterphenyl for P1, P3 or 3,3‴-dicyano-p-quaterphenyl for P2, P4) and hole-transporting fluorophores [N-(2-ethylhexyl)-3,6-bis(styryl)carbazole for P1, P2 or 9,9-dihexyl-2,7-bis(styryl)fluorene for P3, P4] were synthesized and characterized. These poly(aryl ether)s can be dissolved in organic solvents and exhibited good thermal stability with 5% weight-loss temperature above 500°C in nitrogen atmosphere. The photoluminescent (PL) spectra of the films of these polymers showed maximum peaks at around 442-452 nm. The PL spectral results revealed that the emission of polymers was dominated by the fluorophores with longer emissive wavelength via the energy transfer from p-quaterphenyl to 3,6-bis(styryl)carbazole or 2,7-bis(styryl)fluorene segments. Therefore, the p-quaterphenyl segments function only as the electron-transporting/hole-blocking units in these polymers, and the other segments are the emissive centers and hole-transporting units. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital energy levels of these polymers were measured by cyclic voltammetry. The electron-donating nitrogen atom on carbazole resulted in the higher HOMO energy levels of P1 and P2 than those of P3 and P4. The single-layer light-emitting diodes (LED) of Al/poly(aryl ether)s (P1-P4)/ITO glass were fabricated. P1, P2, and P4 revealed blue electroluminescence, but P3 emitted yellow light as a result of the excimer emission.