Deoxyribonucleic Acid Encoded and Size-Defined π-Stacking of Perylene Diimides

Abstract

Natural photosystems use protein scaffolds to control intermolecular interactions that enable exciton flow, charge generation, and long-range charge separation. In contrast, there is limited structural control in current organic electronic devices such as OLEDs and solar cells. We report here the DNA-encoded assembly of π-conjugated perylene diimides (PDIs) with deterministic control over the number of electronically coupled molecules. The PDIs are integrated within DNA chains using phosphoramidite coupling chemistry, allowing selection of the DNA sequence to either side, and specification of intermolecular DNA hybridization. In this way, we have developed a "toolbox" for construction of any stacking sequence of these semiconducting molecules. We have discovered that we need to use a full hierarchy of interactions: DNA guides the semiconductors into specified close proximity, hydrophobic−hydrophilic differentiation drives aggregation of the semiconductor moieties, and local geometry and electrostatic interactions define intermolecular positioning. As a result, the PDIs pack to give substantial intermolecular π wave function overlap, leading to an evolution of singlet excited states from localized excitons in the PDI monomer to excimers with wave functions delocalized over all five PDIs in the pentamer. This is accompanied by a change in the dominant triplet forming mechanism from localized spin−orbit charge transfer mediated intersystem crossing for the monomer toward a delocalized excimer process for the pentamer. Our modular DNA-based assembly reveals real opportunities for the rapid development of bespoke semiconductor architectures with molecule-by-molecule precision.

Strategies for Controlling the Spatial Orientation of Single Molecules Tethered on DNA Origami Templates Physisorbed on Glass Substrates: Intercalation and Stretching

“…For the stretching strategy, any doubly tethered single molecule can be used. Future work will be on building circuits [ 87 ] of single molecules organized in diverse configurations, in which orientation control and small dispersion, as demonstrated here or in future studies addressing different molecular structures, are paramount for the performance of applications, including exciton delocalization [ 88 , 89 , 90 , 91 ] for quantum information science [ 11 ]. Another direction can be on optically monitoring the conformational dynamics [ 92 ] of natural and artificial nanostructures, e.g., DNA-based structures for molecular robotics [ 93 , 94 , 95 ].…”

Molecular Wires for Efficient Long-Distance Triplet Energy Transfer

“…Implementing directed long-distance ΤΕΤ on a single-molecule scale requires building molecular linkers (bridges) that connect TE donors (D) to acceptors (A). ,− It is known that the speed of bridge-mediated D-to-A singlet-exciton transfer (SET) may be improved by enhanced π-stacking interactions between nearest-neighbor molecular bridge (B) units linking D and A. , The π-stacking amplifies the nearest-neighbor SET couplings ( V SET ), leading to delocalized bridge singlet excitons (SE’s) that channel D-to-A SET. − There are many examples of molecular assemblies with enhanced π-stacking interactions. − …”

Activating charge-transfer state formation in strongly-coupled dimers using DNA scaffolds

“…Covalent incorporation of molecular chromophores into synthetic DNA sequences allows for the precise selection of the orientation, position, and number of chromophores upon assembly 26,[30][31][32][33][34] . DNA-based multichromophore systems have been used to control the excited state evolution, including energy transfer pathways and non-radiative decay timescales [35][36][37][38][39][40] . Functional charge separation, a key target for photocatalysis and photovoltaic conversion, has also been achieved through hole transfer to the DNA itself [41][42][43] .…”

“…26,[30][31][32][33][34] DNA-based multichromophore systems have been used to control the excited state evolution, including energy transfer pathways and non-radiative decay timescales. [35][36][37][38][39][40] Functional charge separation, a key target for photocatalysis and photovoltaic conversion, has also been achieved through hole transfer to the DNA itself. [41][42][43] In previous work, the inherent coupling between the properties of the DNA bases and charge-carrier generation and direction limits full spatiotemporal control over charge transport throughout the DNA scaffold.…”