H-bonded effects on novel supramolecular dendrimers containing electron-transporting donor dendrons and single/double H-bonded acceptor emitters

Abstract

Novel asymmetric/symmetric supramolecular dendrimers were constructed by two kinds of (single/double) H-bonded acceptor chromophores, i.e., pyridyl/bispyridyl acceptor emitters, encapsulated with (one or two) 1,3,4-oxadiazole (OXD) donor dendrons in proper acceptor/donor molar ratios. These acceptor emitters were also complexed with another type of dendritic donor cores to form exterior emitting shells reverse to the previous system (with emitting cores) via self-assembly of complementary H- bonded moieties. Because of the shielding effect of bulky OXD dendritic shells in H- bonded donors, the supramolecular dendrimers are able to prevent acceptor emitters from spatial aggregation, and thus to induce glass-forming properties (with T-g) and show stronger emission intensities via H-bonds. Besides, the dendritic donors act as efficient light-harvesting antennae capable of transferring light energy from their peripheral OXD arms to their emitting acceptors, where the chromophore luminance induced by energy transfer is more efficient than that by direct excitation of the emitting cores. Compared with analogous dendritic mixtures without H-bonds, higher quantum yields were observed in the supramolecular dendrimers because of better energy transfer from OXD units. Therefore, compared with acceptor emitters, not only can the emission wavelength be tuned (up to 100 nm of red-shift) by H- bonds, but also much higher emission efficiencies of the H- bonded complexes were induced by reduced aggregation and energy transfer from the OXD donor dendrons.