Synthesis and characterization of highly soluble blue emitting poly(2-vinylanthracene) with 9,10-di(2-naphthalenyl) and 9,10-di(3-quinolinyl) substituents

Two new blue fluorescent polymers poly(910-di(2-naphthalenyl)-2- vinylanthracene) (P(2ADN)) and poly(9,10-di(3-quinolinyl)-2-vinylanthracene) (P(3ADQ)), were polymerized from free radical solution addition polymerization with M_n = 21,500 and 15,400, respectively. The polymers are highly soluble in common organic solvents while P(3ADQ) is also soluble in polar solvents including a 1/1 mixture of ethanol/water. Both polymers are amorphous with excellent thermal stability (T_g (Midpoint) = 343 C and 298 C for P(2ADN) and P(3ADQ), respectively). P(2ADN) exhibited three prominent absorption bands in tetrahydrofuran (364, 383 and 403 nm) and is similar to that of P(3ADQ) (369, 384 and 404 nm). The solid-state Commission Internationale d'Eclairage (CIE_x,y) color coordinates for illumination were (0.15, 0.10) for P(2ADN) and (0.15, 0.13) for P(3ADQ) which lied within the requirements for a true blue display color. The photoluminescence (PL) of the polymers red-shifted 16-17 nm from their respective pendant chromophore 2-methyl-9,10-di(2-naphthalenyl)anthracene (2MADN) and 2-methyl-9,10-di(3- quinolinyl)anthracene (3MADQ) and can be attributed to partial π-π stacking between the adjacent aromatic pendant groups in the polymer chains. The luminescences of 3MADQ and P(3ADQ) are sensitive to pH and the pK_a for the alkalescent 3MADQ and P(3ADQ) calculated was 2.4 and 2.7, respectively. Both polymers have similar band-gap energy (E_g) between 2.88 and 2.91 eV, while the LUMO/HOMO for P(3ADQ) is shifted slightly downward -0.06 to -0.03 eV compared to P(2ADN). The mobility (μ_hole) of the two polymers were measured to be 4.0 × 10^-7 and 10^-8 cm ²/(V-s) for P(2ADN) and P(3ADQ), respectively.