New copolymers with thieno[3,2‐b]thiophene or dithieno[3,2‐b:2′,3′‐d]thiophene units possessing electron‐withdrawing 4‐cyanophenyl groups: Synthesis and photophysical, electrochemical, and electroluminescent properties

• Published in: Journal of polymer science. Part A, Polymer chemistry Polymer chemistry, 2017-08, Vol.55 (16), p.2629-2638
• Main Authors: Výprachtický, Drahomír, Demirtas, Ilknur, Dzhabarov, Vagif, Pokorná, Veronika, Ertas, Erdal, Ozturk, Turan, Cimrová, Věra
• Format: Article
• Language: English
• Subjects: Affinity; Benzonitrile; conjugated polymers; Copolymers; Coupling (molecular); Current voltage characteristics; Diodes; electrochemistry; Electroluminescence; Electron affinity; Emission analysis; Ionization potentials; Molecular orbitals; Monomers; Organic light emitting diodes; Photoluminescence; photophysics; Synthesis; Thin films
• ISSN: 0887-624X; 1099-0518
• DOI: 10.1002/pola.28657

ABSTRACT New monomers containing 4‐cyanophenyl (–PhCN) groups attached to a thieno[3,2‐b]thiophene (TT) or dithieno[3,2‐b:2′,3′‐d]thiophene (DTT) structure were synthesized and characterized as 4‐(2,5‐dibromothieno[3,2‐b]thiophen‐3‐yl)benzonitrile (Br–TT–PhCN) or 4,4′‐(2,6‐dibromodithieno[3,2‐b:2′,3′‐d]thiophene‐3,5‐diyl)dibenzonitrile (Br–DTT–PhCN). The Suzuki coupling of 9,9‐dioctylfluorene‐2,7‐diboronic acid bis(1,3‐propanediol)ester and the Br–TT–PhCN or Br–DTT–PhCN monomer was utilized for the syntheses of novel copolymers poly{9,9‐dioctylfluorene‐2,7‐diyl‐alt‐3‐(4′‐cyanophenyl)thieno[3,2‐b]thiophene‐2,5‐diyl} (PFTT–PhCN) and poly{9,9‐dioctylfluorene‐2,7‐diyl‐alt‐3,5‐bis(4′‐cyanophenyl)dithieno[3,2‐b:2′,3′‐d]thiophene‐2,6‐diyl} (PFDTT–PhCN), respectively. The photophysical, electrochemical, and electroluminescent (EL) properties of these novel copolymers were studied. Their photoluminescence (PL) exhibited the same emission maximum for both copolymers in solution. Red‐shifted PL emissions were observed in the thin films. The PL emission maximum of PFTT–PhCN was more significantly redshifted than that of PFDTT–PhCN, indicating more pronounced excimer or aggregate formation in PFTT–PhCN. The ionization potential (HOMO level) and electron affinity (LUMO level) values were 5.54 and 2.81 eV, respectively, for PFTT–PhCN and were 5.57 and 2.92 eV, respectively, for PFDTT–PhCN. Polymer light‐emitting diodes (LEDs) with copolymer active layers were fabricated and studied. Anomalous behavior and memory effects were observed from the current–voltage characteristics of the LEDs for both copolymers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2629–2638 Copolymers PFTT–PhCN and PFDTT–PhCN were synthesized by Suzuki coupling and the effect of 4‐cyanophenyl groups on their properties was explored. The photoluminescence efficiency was higher for PFDTT–PhCN than for PFTT–PhCN—two times in solution and even five times in the thin films. More pronounced excimer or aggregate formation was found in PFTT—PhCN. Light‐emitting devices (LEDs) made of PFDTT–PhCN exhibited better performance than PFTT–PhCN LEDs. Anomalous current–voltage behavior with memory effects was observed.