Synthesis, photophysical and electrochemical properties of novel carbazole-triazine based high triplet energy, solution-processable materials

Abstract

A series of molecules; tBuCz1SiTrz, tBuCz2SiTrz and tBuCz3SiTrz, which contain carbazole unit as hole-transporting group (donor-D) and triazine unit as electron transporting group (acceptor-A) were synthesized and characterized as high-triplet energy (> 2.9 eV), solution-processable bipolar emitting materials. The conjugation between the D-A groups was interrupted by using bulky tetraphenylsilane groups as spacer aiming to obtain large bandgap and high-triplet energy. The photophysical behaviors of the molecules were investigated by UV-Vis absorption, photoluminescence, phosphorescence, photoluminescence quantum yield and lifetime measurements. Solvent polarity effects were investigated on the intramolecular charge transfer (ICT) behaviour and large solvatochromic effect was observed with the increasing solvent polarity. Electrochemical properties were determined by cyclic voltammetry. All molecules showed oxidation bands arise from the carbazole groups. Reduction bands were originated from the triazine groups and the intramolecular charge transfer between D-A groups. Photophysical, electrochemical and computational characterizations addressed that tBuCz2SiTrz has the weakest ICT character, highest photoluminescence quantum yield (PLQY) and charge balance.

Raman spectroscopy of zinc oxide nanoplatelets modified with ruthenium (II) complexes

“…With the increase of external hydrostatic pressure, the spectra of two complexes considered by Pannwitz et al seem to develop similarities with our spectra; however, their peaks are at somewhat larger wavelengths . To the contrary, the spectra of Ru (II) complexes given by Oner et al in the region above 500 nm exhibit structures centered at somewhat smaller wavelength than is the case with our spectra . The spectra corresponding to all the modified samples are similar to those considered by McConnell et al with respect to detecting DNA defects .…”

Phosphine Sulfide-Based Bipolar Host Materials for Blue Phosphorescent Organic Light-Emitting Diodes

“…It is well known that carrier transporting balance is of particular importance to render the holes, and electrons recombine in the emitting layer so that high-performance OLEDs can be achieved [ 32 ]. In addition, introducing more carbazole groups into molecule skeletons would increase the hole-transporting ability of the compounds [ 33 , 34 , 35 ]. Hence, it is rational to deduce that the poorer device performances of Device B and Device C might be ascribed to the increased number of carbazoles in the host molecules, which enhance the hole-transporting ability of the devices, thus deteriorating the carrier transporting balance.…”

The impact of phenyl–phenyl linkage on the thermodynamic, optical and morphological behavior of carbazol derivatives

“…According to recent reports, the short conjugation of carbazole derivatives leading to a wide band gap is a key factor for the high triplet energy presented by this class of semiconductors. 24,[60][61][62][63] Optical band gaps (E g ) of 3.57, 3.51 and 3.59 eV were estimated from the absorption edge wavelengths (l abs.edge ) of the UV-vis spectra for mCP, CBP and TCB, respectively (E g z 1240/l abs.edge ). These values are in nice agreement with literature reports presented by other authors for samples studied in DCM solution and/or in the thin-lm state.…”

“…[19][20][21][22] Likewise, carbazole derivatives have also gathered research interest due to the low-cost and good charge transport ability of the carbazolyl moiety. [23][24][25] Carbazol unit provides a wide range of charge transport molecules, such as carbazole-based HTMs with triphenylamine moieties, which have been explored as promising candidates for highperforming perovskite solar cells. [26][27][28] Moreover, carbazole compounds are very relevant in developing phosphorescent organic light-emitting diodes (PHOLEDs), where these compounds act as the host materials, mainly due to their high triplet state energy and excellent hole transport capability.…”