Insight into the mechanism and outcoupling enhancement of excimer-associated white light generation

Fundamental insight into excimer formation has been gained by using 9,10-bis[4-(9-carbazolyl)phenyl]anthracene] ( Cz 9 PhAn ) as a probe. Cz 9 PhAn exhibits a highly emissive blue fluorescence in solution and is found to emit a panchromatic white light spectrum (400-750 nm) in film, powder and single crystal, in which an additional excimer band appears at ∼550 nm. Detailed structural analyses, emission relaxation dynamics and a theoretical approach conclude the formation of an anthracene*/phenyl ring excimer through an overlap between π* (anthracene) and π (phenyl ring) orbitals in a face-to-edge stacking orientation. The rate of excimer formation is determined to be 2.2 × 10 9 s −1 at room temperature, which requires coupling with lattice motion with an activation energy of 0.44 kcal mol −1 . Exploiting Cz 9 PhAn as a single emitter, a fluorescent white organic light emitting diode (WOLED) is fabricated with a maximum external quantum efficiency ( η ext ) of 3.6% at 1000 cd m −2 (4.2 V) and Commission Internationale de L'Eclairage (CIE) coordinates of (0.30, 0.33). The white-light Cz 9 PhAn reveals a preferred orientation of the transition dipole moment in the emitting layer to enhance light outcoupling. This non-doped, single component ( Cz 9 PhAn ) WOLED greatly reduces the complexity of the fabrication process, rendering a green and cost-effective alternative among the contemporary display/lighting technologies. Fundamental insight into excimer formation of Cz 9 PhAn , achieving a single-component, high-performance WOLED.