Substituted acridones: simple deep blue HIGHrISC emitters in an aprotic environment

<i>N</i>-Methylacridones (NMAs) substituted at positions 2 and 7 with +M groups (fluorine and methoxy) were synthesized and characterized by steady-state and time-resolved spectroscopy. Solutions of the NMA derivatives in an aprotic solvent (tetrahydrofuran) emit in the deep blue region of the visible spectrum with radiative rate constants larger than 5.4 × 10⁷ s^-1 and fluorescence quantum yields up to 0.84. Sensitization experiments employing 1,4-dichlorobenzene give evidence for HIGHrISC behavior of the NMAs, that is, reverse intersystem crossing (rISC) from a higher triplet state T_<i>n</i>≥2 occurs. The spectroscopic results, which are corroborated by quantum chemical calculations, render these derivatives very promising for applications in organic light emitting diodes (OLEDs).