PCPP derivatives containing carbazole pendant as hole transporting moiety for efficient blue electroluminescence

Abstract

The syntheses and characterization of poly ((2,6-(4,4-bis(4-((2-ethylhexyl) oxy)phenyl)-4H-cyclopenta[def]phenanthrene))-co-(2,6-(4,4-bis(4-(((9-carbazolyl)hexyl) oxy)phenyl))-4H-cyclopenta[def]phenanthrene)) (BCzPh-PCPPs) and poly((2,6-(4,4-bis (4-((2-ethylhexyl)oxy)phenyl)-4H-cyclopenta[def]phenanthrene))-co-(2,6-(4-(4-(((9-carbazolyl)hexyl)oxy)phenyl)-4-(4-((2-ethylhexyl)oxy)phenyl)-4H-cyclopenta[def]phenanthrene))) (CzPh-PCPPs), with carbazole unit as pendants, are presented. The carbazole moiety, which can improve the hole injection ability, was introduced as a pendant on the PCPP backbone. The devices of the polymers with the configurations of ITO/PEDOT:PSS/polymers/Ca/Al generate EL emission with maximum peaks at 400-450 nm, CIE coordinates of (x ¼ 0.11-0.29, y ¼ 0.11-0.33), low turn-on voltages of 4-6 V, maximum brightness of 60-810 cd/m 2 , and luminescence efficiencies of 0.04-0.22 cd/A. The PL spectra of CzPh-PCPPs films did not show any peak at around 550 nm, which corresponds to keto defect or aggregate/excimer formation, even after annealing for 30 h at 150 C in air. Out of the series, CzPh-PCPP1 (PCPP derivative with 10% of carbazole moiety as pendant) shows blue emission with the maximum brightness of 810 cd/m 2 at 9 V, and the highest luminescence efficiency of 0.22 cd/A at 395 mA/cm 2 .

Synthesis of High Molecular Weight 1,4-Polynaphthalene for Solution-Processed True Color Blue Light Emitting Diode

“…We have estimated the lowest unoccupied molecular orbital (LUMO) energy level of P1a from the onset of the cyclic voltammetry (CV) reduction wave (Figure ). LUMO ( E LUMO CV ) was obtained at −2.48 eV with respect to the redox potential of ferrocene measured from vacuum level (−4.8 eV). , Because the corresponding oxidation potential was not obtained from CV, the highest occupied molecular orbital (HOMO) energy level was calculated considering the optical band gap ( E g OPT = 3.51 eV) obtained from the onset of the absorption spectrum. HOMO was calculated to be −5.99 eV using the equation E HOMO OPT = E LUMO CV – E g OPT .…”

“…Organic π-conjugated polymers are in the center of research owing to their robust electroluminescence (EL) characteristics offering potential in organic light emitting diodes (OLEDs) applications. , Organic π-conjugated materials are widely suitable for OLED applications as active material because of their band gap tunability that determines the color of the emitted light from the device. , While low band gap polymers are largely synthesized for the generation of luminescence at higher wavelengths in the visible spectrum, suitable polymers with large band gap for the generation of blue luminescence were rarely reported until date. − Color pure blue emitting polymers are extremely important in optoelectronic applications such as color tunable displays or for white light generation by mixing red–green–blue colors. − Therefore, synthesis of color pure blue emitting polymer that meets the Commission Internationale de ĺEclairage (CIE) coordinates (0.14, 0.08) defined by National Television Standards Committee (NTSC) is important for high precision display applications …”

“…Pure blue electroluminescent polymers are relatively rare and mostly composed of fluorene-based polymers. − Therefore, current research in the field of OLEDs relies on developing new blue emitting materials, particularly organic π-conjugated semiconducting polymers. While blue emitting OLEDs were mostly developed from polymers containing fluorene units, − polymers with carbazole, pyrene, poly­( p -phenylene), , p -phenylenevinylene, and triphenylphosphine/triphenylphosphine oxide units have also been reported. Naphthalene-based molecules attribute large band gaps; hence, these are suitable for blue luminescence.…”