Controlling Symmetry-Breaking Charge Separation in Pyrene Bichromophores

Abstract

So far, symmetry-breaking charge separation (SB-CS) has been observed with a limited number of chromophores and is usually inhibited by the formation of an excimer. We show here that thanks to fine-tuning of the interchromophore coupling via structural control, SB-CS can be operative with pyrene, despite its high propensity to form an excimer. This is realized with a bichromophoric system consisting of two pyrenes attached to a crown ether macrocycle, which can bind cations of different sizes. By combining stationary and timeresolved spectroscopy together with molecular dynamics simulations, we demonstrate that the excited-state dynamics can be totally changed depending on the binding cation. Whereas strong coupling leads to rapid excimer formation, too weak coupling results in noninteracting chromophores. However, intermediate coupling, achieved upon binding of Mg 2+ , allows for SB-CS to be operative.

Symmetry-Breaking Charge Separation Mediated Triplet Population in a Perylenediimide Trimer at the Single-Molecule Level

“…Our longstanding efforts to access long-lived triplet excitons in organic chromophores motivated us to explore potential strategies for triplet generation in multichromophoric systems. , In this work, we reveal triplet excited-state population via ultrafast intramolecular SB-CS in a rigid perylenediimide trimer ( PDI-T ). The weak excitonically coupled PDI-T exhibits rigid ground- and excited-state structures, thereby suppressing the excimer formation channels. , SMFM measurements of PDI-T reveal contrasting blinking dynamics in a polar poly­(vinyl alcohol) matrix compared to a nonpolar polystyrene matrix. In agreement with the single-molecule analysis, femtosecond and nanosecond transient absorption measurements of PDI-T at the ensemble level substantiate ultrafast SB-CS leading to the triplet state population in polar solvents.…”