Magic-Angle Exciton Coupling in a Molecular Solid: Optical Consequence of Null-Coulombic Coupling.

Instances of magic angle excitonic coupling and its optical consequences are infrequently documented in the literature, yet they hold fundamental significance in understanding excited state electronic processes within molecular aggregates. Weak/null long-range dipolar Coulombic coupling is the characteristic of chromophore arrays positioned in a magic angle configuration. This study presents a rare example of such phenomena in CFDPT solids, resulting in a high fluorescence quantum efficiency of 62 ± 3% in the aggregated solid state. Supported by computational calculations, we validate our experimental findings of null-Coulombic coupling and significant charge transfer (CT) coupling within the solid state.