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Strongly-coupled multichromophoric assemblies orchestrate the absorption, transport, and conversion of photonic energy in natural and synthetic systems. Programming these functionalities involves the production of materials in which chromophore placement is precisely controlled. DNA nanomaterials have emerged as a programmable scaffold that introduces the control necessary to select desired excitonic properties. While the ability to control photophysical processes, such as energy transport, has been established, similar control over photochemical processes, such as interchromophore charge transfer, has not been demonstrated in DNA. In particular, charge transfer requires the presence of close-range interchromophoric interactions, which have a particularly steep distance dependence, but are required for eventual energy conversion. Here, we report a DNA-chromophore platform in which long-range excitonic couplings and short-range charge-transfer couplings can be tailored. Using combinatorial screening, we discovered chromophore geometries that enhance or suppress photochemistry. We combined spectroscopic and computational results to establish the presence of symmetry-breaking charge transfer in DNA-scaffolded squaraines, which had not been previously achieved in these chromophores. Our results demonstrate that the geometric control introduced through the DNA can access otherwise inaccessible processes and program the evolution of excitonic states of molecular chromophores, opening up opportunities for designer photoactive materials for light harvesting and computation.

Recently the supramolecular assembly of DNA conjugates has caught attention in supramolecular chemistry. DNA offer some unique characteristics allowing the design of complex nanostructures. The DNA framework allows the defined spatial arrangement of modifications. In previous work DNA was modified with phenanthrene sticky ends forming vesicular supramolecular assemblies with light-harvesting properties.[1] Interestingly, E-tetraphenylethylenes modifications at the 3’-ends of DNA led to aggregation-induced emission (AIE) active assemblies.[2] In this work, we modified a DNA strand at the 3’- and 5’-end with 2,7-pyrene (Figure 1A). AFM measurements of the 2,7-pyrene-DNA conjugates revealed their self-assembly into vesicles (Figure 1B). In addition to AFM studies, fluorescence and UV-vis spectroscopy measurements will be presented and discussed.

The supramolecular assembly of DNA conjugates has caught attention in supramolecular chemistry. DNA bears some unique features enabling the design of complex nanostructures. The DNA framework offers a defined spatial arrangement of modifications. In preceding work DNA was modified with phenanthrene at the 3’-ends of DNA forming vesicular supramolecular assemblies with unique light-harvesting properties.[1] Interestingly, the modification of DNA with E-tetraphenylethylenes sticky ends led to aggregation-induced emission (AIE) active assemblies.[2] In this work, we modified a DNA strand at the 3’- and 5’-end with 1,6-pyrene (Figure 1A). We varied the length of the sticky ends to compare their self-assembly properties (1, 2, and 3 pyrene units on either side). For example, AFM measurements of the 1,6-pyrene-DNA conjugates with a total of 6 pyrene units revealed their self-assembly into vesicles (Figure 1B). In addition to AFM studies, fluorescence and UV-vis spectroscopy measurements will be presented and discussed.

Tetrathiafulvalene (TTF)-based donor-acceptor (D–A) ensembles have attracted a lot of attention due to their unique (opto)electronic properties and potential applications in organic semiconductors, photovoltaics, sensors, switches and molecular electronics.1-3 To develop high-performance electronic devices, control over multiple charge-transfer (CT) pathways in D-A ensembles is of prime importance. Recently, we have demonstrated chemical and ultrafast optical regulation of distinct photo-induced charge flows within such D-A systems.4,5 As a continuation of our ongoing work, we herein describe redox and optical properties of new D–A ensembles (Chart 1) which were prepared by covalent linkage of two TTF donor units to a central azapyrene acceptor either with or without two tert-butyl groups. A detailed experimental and theoretical study of electronic interactions between D and A units and ICT processes in these triads is presented.

Graphene films have attracted a lot attention due to their potential application in nanoelectronic devices. Noncovalent functionalization of graphene does not disrupt the extended π-conjugation. Incorporation of intercalators in the form of redox- and/or photoactive building blocks enables the usage of electron donor-acceptor (D–A) interactions. Accordingly, the noncovalent functionalization of nanographene (NG) or graphene sheets with either aromatic electron donors or acceptors, as demonstrated in the case of carbon nanotubes, is widely exploited in contemporary research. Herein, we report the exfoliation of graphite via intercalation and immobilization of planar pi-conjugates tetrathiafulvalene–perylenediimide (TTF–PDI). The resultant nanohybrids have been characterized by complementary spectroscopic and microscopic techniques.

The self-assembly of 3,6-disubstituted phenanthrene trimers with phosphodiester-bridges leads to the formation of supramolecular fibers. Previously, it was shown that these fibers act as an efficient light-harvesting antenna. So far, the acceptor was incorporated into an oligomer and added as such. Our new approach enables us to use various monomeric chromophores: the polyaromatic acceptor is added during the self-assembly process of the forming supramolecular polymer. Upon excitation of the phenanthrene units the energy is transferred to the acceptor, which emits the light in an increased intensity. Benzo(a)pyrene reached as one of the highest fluorescence quantum yield of 31% at an acceptor/phenanthrene ratio of 12 mol-%. The fibers were analyzed by microscopy (AFM, UV-vis, fluorescence). This allows us to detect small amounts of chromophores in an aqueous medium.

Tetrathiafulvalene(TTF)-fused donor-acceptor (D–A) ensembles are of high interest due to their unique (opto)electronic properties and potential applications in organic conductors, photovoltaics, sensors, switches and molecular electronics. A direct annulation of a TTF with a variety of electron-acceptors has been achieved for studying photo-induced intramolecular charge transfer (ICT) as well as the photogeneration of long-lived charge separated states in resultant D-A systems. Herein, we describe redox and optical properties of a new D–A ensemble (Chart 1) which was prepared by complexation of BF2 with a TTF-fused 2,3-di(1H-2-pyrrolyl)quinoxaline ligand. A detailed experimental and theoretical study of an ICT process in TTF-QB is presented.

Dispersions of preexfoliated nanographene (NG) and fused electron donor–acceptor tetrathiafulvalene–perylenediimide (TTF–PDI) enable multifunctional, noncovalently functionalized NG. They were characterized by complementary spectroscopic and microscopic techniques. The design strategy of the chromophoric and electroactive molecular conjugate renders a large and planar π-extended system with a distinct localization of electron-rich and electron-poor parts at either end of the molecular conjugate. Within the in-situ formed nanohybrid, the conjugate was found to couple electronically with NG preferentially through the electron accepting PDI rather than the electron donating TTF and to lead to p-doping of graphene.