Highly Isotactic Poly(N-butenyl-carbazole): Synthesis, Characterization, and Optical Properties

Abstract

The synthesis of isotactic poly(N-butenyl-carbazole) (i-PBK) by using homogeneous isospecific Ziegler-Natta catalytic system is reported. The achieved polymer is crystalline and shows, to DSC and X-ray analysis, two distinct crystalline phases.i-PBK FTIR spectrum and X-ray diffraction pattern are compared with those of poly(N-vinylcarbazole) (PVK). The observed differences are tentatively associated with higher flexibility of thei-PBK chains due to the alkylene group connecting the carbazole group to the main chain.i-PBK optical properties are also compared with those of PVK and isotactic poly(N-pentenyl-carbazole) (i-PPK), a higher homologue ofi-PBK recently used as emitting layer in organic light emitting diodes (OLEDs) showing white light emission. The close similarity of the fluorescence spectra ofi-PBK andi-PPK is a promising basis for optical applications of this polymer.

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

“…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 . It is worth noting that the most interesting result of our previous experimental studies is that the excimer formation is essentially driven by the polymer tacticity.…”

“…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) …”

“…It is worth noting that the most interesting result of our previous experimental studies is that the excimer formation is essentially driven by the polymer tacticity. In detail, in the solid state, highly isotactic polymers favor the formation of sandwich‐like excimer, while highly syndiotactic polymers give rise to partially overlapping excimers . Of course, the different optical properties of two different stereoisomers of the same polymer can also induce a different electroluminescent behavior.…”