Accelerating Symmetry-Breaking Charge Separation in an Angular versus Linear Perylenediimide Dimer through the Modulation of Coulombic Coupling.

Achieving faster charge separation in organic systems capable of mimicking the electron transfer events in natural photosynthesis has been an exciting research topic for several decades. Herein, we demonstrate the orientation-dependent acceleration of symmetry-breaking charge separation (SB-CS) in an angular (A-PDI2) versus linear (L-PDI2) perylenediimide dimer. Femtosecond transient absorption measurements reveal ultrafast SB-CS in A-PDI2 (τCS = 6.3 ps) with charge separation ∼20 times faster than in L-PDI2 (τCS = 127.9 ps). Nanosecond transient absorption measurements establish the negligible population of triplet excited-states in L-PDI2 (ϕT < 1%), whereas a significant triplet excited-state population (ϕT = 35.9%) is quantified in A-PDI2. The theoretically computed Coulombic coupling strength in A-PDI2 (|JCoul| = 14.9 cm-1) and L-PDI2 (|JCoul| = 438.4 cm-1) is rationalized as the crucial factor modulating the SB-CS rates. The current investigation could be beneficial for designing light harvesting materials capable of faster charge separation for efficient optoelectronic devices.