Dual-core star-shaped single white polymers: the effect of host structure on luminescence properties

Investigation of Energy Transfer in Star-Shaped White Polymer Light-Emitting Devices via the Time-Resolved Photoluminescence

A series of white polymer light-emitting devices (WPLEDs) were fabricated by utilizing star-shaped white-emission copolymers containing tri[1-phenylisoquinolinato-C2,N]iridium (Ir(piq)₃), fluorenone (FO) and poly(9,9-dioctylfluorene) (PFO) as red-, green- and blue-emitting (RGB) components, respectively. In these WPLEDs, a maximum current efficiency of 6.4 cd·A⁻¹ at 20 mA·cm⁻² and Commission Internationale d’Eclairage (CIE) coordinates of (0.33, 0.32) were achieved, and the current efficiency was still kept to 4.2 cd·A⁻¹ at the current density of 200 mA·cm⁻². To investigate energy transfer processes among the three different chromophores of the star-shaped copolymers in these WPLEDs, the time-resolved photoluminescence (PL) spectra were recorded. By comparing the fluorescence decay lifetimes of PFO chromophores in the four star-like white-emitting copolymers, the efficient energy transfer from PFO units to Ir(piq)₃ and FO chromophores was confirmed. From time-resolved PL and the analysis of energy transfer process, the results as follows were proved. Owing to the star-like molecular structure and steric hindrance effect, intermolecular interactions and concentrations quenching in the electroluminescence (EL) process could also be sufficiently suppressed. The efficient energy transfer also reduced intermolecular interactions’ contribution to the enhanced device performances compared to the linear single-polymer white-light systems. Moreover, saturated stable white emission results from the joint of energy transfer and trap-assisted recombination. This improved performance is expected to provide the star-like white-emitting copolymers with promising applications for WPLEDs.

Diarylmaleimide-based branched oligomers: strong full-color emission in both solution and solid films

An effective design method is presented to construct highly efficient fluorescent materials in both solution and solid films, by non-conjugately linking fluorophores into branched oligomers. Surface aryl groups are changed to tune the luminescent color from blue (λ_em = 480 nm) to red (λ_em = 651 nm), and realize full-color emission.