LAUSR

Unlike conventional thermally activated delayed fluorescence chromophores, boron-centered azatriangulene-like molecules combine a small excited-state singlet-triplet energy gap with high oscillator strengths and minor reorganization energies. Here, using highly correlated quantum-chemical calculations, we report this is driven by short-range reorganization of the electron density taking place upon electronic excitation of these multi-resonant structures. Based on this finding, we design a series of π-extended boron- and nitrogen-doped nanographenes as promising candidates for efficient thermally activated delayed fluorescence emitters with concomitantly decreased singlet-triplet energy gaps, improved oscillator strengths and core rigidity compared to previously reported structures, permitting both emission color purity and tunability across the visible spectrum.Thermally activated delayed fluorescence is a mechanism for enhancing the efficiency of organic light emitting diodes by harvesting triplet excitons, but there is still a need to design more efficient materials. Here, the authors rationally design and characterize a series of π-extended boron- and nitrogen-doped nanographenes as promising candidates.