Star-Shaped Molecules with Indolo[3,2,1-jk]carbazole Core: a Comprehensive Study of Light-Emitting Materials.

Abstract

Novel star-shaped derivatives of indolo[3,2,1-jk]carbazole (ICz) were obtained and thoroughly studied. They incorporate large chromophores, specifically fluorene(ICz-A), carbazole(ICz-B), phenothiazine(ICz-C), and phenothiazine-carbaldehyde(ICz-D), all with long alkyl chains attached to the ICz core via acetylene linkages. The impact of different donor-acceptor substituents on optical, thermal, electrochemical, and electroluminescent properties of ICz derivatives has been systematically investigated and compared with the quantum chemical calculations. ICz derivatives in DCM solution exhibit photoluminescence across a spectrum, from deep blue to green. In the solid state, bathochromic shifts of the emission maxima were observed for all compounds, indicating interactions between molecules in the condensed phase. The ICz-D exhibits the highest emission efficiency in the solid state accompanied with the reduction in the FWHM of the emission peak, attributed to distorted plane of this molecule. The presence of "butterfly" phenothiazine rings and the aldehyde groups prevents electron transfer through intermolecular channels by acting as efficient blockers. For all compounds their ability for light emission under external voltage was tested, based on devices with a neat compound (ITO/PEDOT:PSS/ICz/Al) and with guest-host configuration (ITO/PEDOT:PSS/PVK:PBD:ICz/Al). In the electroluminescence spectra of all diodes one emission band in the 450-800 nm range was detected. Moreover, some of them exhibited voltage-dependent color variation.