[4]Cyclo-N-alkyl-2,7-carbazoles: Influence of the Alkyl Chain Length on the Structural, Electronic, and Charge Transport Properties

Abstract

Macrocycles possessing radially oriented π−orbitals have experienced a fantastic development. However, their incorporation in organic electronic devices remains very scarce. In this work, we aim at bridging the gap between organic electronics and nanorings by reporting the first detailed structure-properties-device performance relationship study of organic functional materials based on a nanoring system. Three [4]cyclo-N-alkyl-2,7-carbazoles bearing different alkyl chains on their nitrogen atoms have been synthesized and characterized by combined experimental and theoretical approaches. This study includes electrochemical, photophysical, thermal and structural solid-state measurements and charge transport properties investigations. An optimized protocol of the Pt approach has been developed to synthesize the [4]-cyclocarbazoles in high yield (52-64%), of great interest for further development of nanorings especially in materials science. The charge transport properties of [4]-cyclocarbazoles and a model compound, [8]-cycloparaphenylene ([8]CPP), have been studied. Although no field effect (FE) mobility was recorded for benchmark [8]CPP, FE mobility values of ca 10 -5 cm².V -1 .s -1 were recorded for the [4]-cyclocarbazoles. The characteristics (threshold voltage VTH, subthreshold swing SS, trapping energy ∆E) recorded for the three[4]-cyclocarbazoles appear to be modulated by the alkyl chain length borne by the nitrogen atoms. Remarkably, the space-charge-limited current mobilities measured for the [4]-cyclocarbazoles are about 3 orders of magnitude higher than that of [8]CPP (1.37/ 2.78×10 -4 for the [4]-cyclocarbazoles vs 1.21×10 -7 cm².V -1 .s -1 for [8]CPP) highlighting the strong effect of nitrogen bridges on the charge transport properties. The whole study opens the way to the use of nanorings in electronics, which is now the next step of their developments.

Rhodium‐Catalyzed Intermolecular Cycloaromatization Route to Cycloparaphenylenes that Exhibit Aggregation‐Induced Emission

“…[21] Their emission maxima (482-491 nm) are blue-shifted compared with that of the [8]CPP (528 nm). [20] Their absolute fluorescence quantum yields are very low (0.015 or less), however, AIE was observed in these CPPTs, which exhibit green-yellow emission (λ max = 508-575 nm) with increased fluorescence quantum yields (0.036-0.147) in the powder states. On the contrary, the fluorescence quantum yield of [8]CPP in the film state (0.08) is lower than that in a cyclohexane solution (0.25).…”

“…Their absolute fluorescence quantum yields are very low (0.015 or less), however, AIE was observed in these CPPTs, which exhibit green‐yellow emission (λ max =508–575 nm) with increased fluorescence quantum yields (0.036–0.147) in the powder states. On the contrary, the fluorescence quantum yield of [8]CPP in the film state (0.08) is lower than that in a cyclohexane solution (0.25) [20] . CPPT 12 bearing the highly electron‐deficient phthalimide moiety also showed AIE and exhibited significantly red‐shifted emission (λ max =607 nm) compared with CPPTs 5 a – e in the powder state.…”

“…On the contrary, the fluorescence quantum yield of [8]CPP in the film state (0.08) is lower than that in a cyclohexane solution (0.25). [20] CPPT 12 bearing the highly electron-deficient phthalimide moiety also showed AIE and exhibited significantly red-shifted emission (λ max = 607 nm) compared with CPPTs 5 a-e in the powder state.…”

“…The photophysical data of [8]CPPTs 5 a – e are summarized in Table 2 compared with the data of [8]CPP. The UV‐Vis absorption maxima in THF (336–340 nm) are similar to that of the [8]CPP (333 nm), [20] but with a shoulder peak attributed to the triphenylene moiety (256–259 nm) [21] . Their emission maxima (482–491 nm) are blue‐shifted compared with that of the [8]CPP (528 nm) [20] .…”

“…The UV‐Vis absorption maxima in THF (336–340 nm) are similar to that of the [8]CPP (333 nm), [20] but with a shoulder peak attributed to the triphenylene moiety (256–259 nm) [21] . Their emission maxima (482–491 nm) are blue‐shifted compared with that of the [8]CPP (528 nm) [20] . Their absolute fluorescence quantum yields are very low (0.015 or less), however, AIE was observed in these CPPTs, which exhibit green‐yellow emission (λ max =508–575 nm) with increased fluorescence quantum yields (0.036–0.147) in the powder states.…”