Synthesis and Spectroscopy of Poly(9,9-dioctylfluorene-2,7-diyl-co-2,8-dihexyldibenzothiophene-S,S-dioxide-3,7-diyl)s: Solution-Processable, Deep-Blue Emitters with a High Triplet Energy

Poly(9,9-dioctylfluorene-2,7-diyl- co -2,8-dihexyldibenzothiophene- S,S -dioxide-3,7-diyl) copolymers (pF-S 6 8 − 10 ) of varying composition have been synthesized by Suzuki−Miyaura polymerization. The hexyl substituents on the dibenzothiophene- S,S -dioxide (S) units improve the solubility of the copolymers and increase the dihedral angles in the backbone; this shifts the emission deep into the blue (λ max 420 nm for films of 10 ) and increases the photoluminescence quantum yield compared with previous pF-S copolymers containing non-alkylated S units. The backbone twist restricts formation of the intramolecular charge transfer (ICT) state for low incorporation ratios of S 6 units. The triplet energy of these new copolymers increases as the percentage of the S 6 unit increases (i.e., 15, 30, 50%: 8 → 9 → 10 ). The alternating copolymer 10 has a sufficiently high triplet energy ( E T 2.46 eV for onset of phosphorescence) to host a green phosphorescent iridium guest emitter, as demonstrated in electroluminescence studies which showed emission exclusively from the guest complex.