Broadband spectra with fluorescence and phosphorescence dual emission from bichromophoric platinum metallomesogens containing a 6,12-dihydro-indeno[1,2-b]fluorene linkage

Abstract

Two binuclear platinum metallomesogens possessing a 6,12-dihydro-indeno[1,2-b]fluorene bridge, FJ-1 and FJ-2, have been synthesised and characterised by ¹H and ¹³C NMR, TOF-MS and elemental analysis. Their thermal properties were studied by polarised optical microscopy and differential scanning calorimetry. Upon photoexcitation in solution, both complexes exhibited dual fluorescence (¹π–π*)/phosphorescence (³π–π*) emission covering most of the visible spectrum (from about 460 nm to 750 nm). This uncommon behaviour has been further investigated by time-resolved optical spectroscopy, including nanosecond time-resolved transient absorption spectroscopy, and further insights were obtained by means of density functional theory (DFT) and time-dependent DFT (TD-DFT). An organic light-emitting diode (OLED) using FJ-1 was prepared. Importantly the two emission bands are retained in electroluminescence. This result suggests that controlling spin–orbit coupling to obtain dual emission can provide an effective way of achieving broadband emission based on a single molecule.