Synthesis, characterization, and use as emissive layer of white organic light emitting diodes of the highly isotactic poly(N‐pentenyl‐carbazole)

Abstract

The synthesis and the microstructural characterization of isotactic poly (N‐pentenyl‐carbazole) (i‐PPK) are reported. The achieved polymer is semicrystalline, the melting temperature is 138°C. i‐PPK Fourier transform infrared spectroscopy (FTIR) spectrum and X‐ray diffraction pattern are compared with those of polyvinylcarbazole. The observed differences are tentatively associated to higher flexibility of the i‐PPK chains due to the alkylene group connecting the carbazole group to the main chain. The presence of intrachain and interchain interactions between carbazole units, which bring these groups to stack each other, is assumed. i‐PPK optical properties are investigated and an electroluminescent behaviour of polymer is observed. Organic light emitting diodes based on i‐PPK layers are founded to emit white light. POLYM. COMPOS., 36:1110–1117, 2015. © 2015 Society of Plastics Engineers

Optoeletronic properties of poly(N‐alkenyl‐carbazole)s driven by polymer stereoregularity

“…Consistently with these observations, the fluorescence spectra of diluted solutions of our synthesized stereoregular polymers collected at room temperature do not exhibit excimer emission, but only the monomer fluorescence is observed. Conversely, we found that all our synthesized stereoregular polymers in the solid state as thin films, show both sandwich‐like and “partially overlapped” excimer emissions . These results were explained assuming that polymer chain conformational freedom in solution prevents excimer formation, while on the other side, in the solid state and at temperatures lower than glass transition temperature ( T g ), a reduced conformational freedom allows the excimer formation .…”

“…Starting from PVK, several polymers with novel molecular structures have been prepared . It is well known that PVK optical properties are related to the peculiar structural feature of the polymer giving rise to two spectrally distinct excimer fluorescences .…”

“…Recently, some of us reported the synthesis of several higher homologues of PVK with high stereoregularity degree, that is, isotactic poly( N ‐butenyl‐carbazole) ( i ‐PBK), isotactic and syndiotactic poly( N ‐pentenyl‐carbazole) ( i ‐PPK and s ‐PPK, respectively), and isotactic and syndiotactic poly(4‐(N‐carbazolyl)methyl styrene) ( i ‐PSK and s ‐PSK, respectively) . All stereoregular polymers were obtained by Ziegler‐Natta (Z‐N) homogeneous polymerization, that is, a polymerization process failing for the synthesis of PVK due to the conjugation of the vinyl group with the carbazole aromatic system of the monomer (9‐vinylcarbazole) …”

Recent Advances in Polymer Organic Light-Emitting Diodes (PLED) Using Non-conjugated Polymers as the Emitting Layer and Contrasting Them with Conjugated Counterparts

“…19) by a homogeneous Ziegler-Natta catalytic system of rac-[(CH 3 ) 2 Si(indenyl) 2 ]ZrCl 2 and methylallumoxane (MAO) in toluene at 20°C. 63 Interestingly, i-PPK film showed a broad emission spectrum from 350 nm to 600 nm, probably due to the presence of singlet and triplet excimers similar to the case of poly(N-vinylcarbazole). 56 Given the broad emission, i-PPK was an ideal candidate for white PLED device [ITO/PEDOT:PSS (40 nm)/i-PPK (70 nm)/ BCP (10 nm)/Alq 3 (10 nm)/Ca (30 nm)/Al (70 nm)] which gave a broad electroluminescence spectrum covering from 400 nm to 800 nm with three peaks at 420 nm, 520 nm, and 620 nm.…”

“…Indeed, the PLQYs of non-conjugated fluorescent polymers are competitive (up to 61% in THF) 61 and the surface roughness seems to not depend on the nature of the polymer backbone (R a < 1 nm). 26,63 Considering the key difference between fluorescent polymers and phosphorescent/TADF analogues is the utilization of triplet excitons for emission in the latter two types of materials, one might wonder if the nature of the polymer backbone affected the exciton utilization efficiency (g S ), hence, resulting in the remarkably different PLED efficiencies demonstrated by non-conjugated and conjugated fluorescent polymers. The internal quantum efficiency (IQE) of PLED is strongly related to g S according to the following expression 138 :…”