Symmetry-breaking Charge Transfer Research Articles

Overcrowded 14,14'-Bidibenzo[a,j]anthracenes:Challenges in Syntheses and Atypical Property of Lacking Symmetry-Breaking Charge Transfer (SBCT).

14,14'-Bidibenzo[a,j]anthracenes (BDBAs) were prepared byiridium-catalyzed annulation of5,5'-biterphenylenewith alkynes.OvercrowdedBDBAs withhighly distorted molecularhalvesand asmallinterplanarangle between twoanthryl moieties (down to approximately 31º, currently the lowest reported value)wereverified by X-ray crystallography.Thestrong intramolecular interactions and electronic couplingsbetween two molecular halvesresulted in upfield1H NMR signals, redshifted absorption and emission bands, and areduced HOMO-LUMO gap.Photodynamic investigations on BDBAs indicated thatthe formationof the conventional symmetry-breakingcharge transfer (SBCT) state was suspended byrestricted rocking around the central C-Cbond. Such a mechanism associated withthishighly constrainedconformation was examined for the first time.

Sulfone-Functionalized Chichibabin's Hydrocarbons: Stable Diradicaloids with Symmetry Breaking Charge Transfer Contributing to NIR Emission beyond 900 nm.

While monoradical emitters have emerged as a new route toward efficient organic light-emitting diodes, the luminescence property of organic diradicaloids is still scarcely explored. Herein, by devising a novel radical-radical coupling-based synthetic approach, we report a new class of sulfone-functionalized Chichibabin's hydrocarbon derivatives, SD-1-3, featuring varied substituent patterns and moderate to high diradical characters of 0.44-0.70, as highly stable diradicaloids with rarely seen NIR emission beyond 900 nm. Via comprehensive experimental and theoretical investigations, we reveal that the optoelectronic and magnetic properties of these materials are significantly tuned by the variations of substitutions (H/CF3/OMe) on the molecular skeletons. More importantly, quantum chemical computations indicate that the embedding of sulfone groups has contributed to a breaking of their quasi-C2 symmetry of these diradicaloid molecules and results in an excited-state charge transfer character. Therefore, a remarkably deep NIR emissive wavelength of up to 998 nm, together with a large Stokes shift (∼386 nm), is achieved for the CF3-based SD-2 molecule in tetrahydrofuran. To the best of our knowledge, such a luminescent wavelength of SD-2 has represented the longest wavelengths among the currently reported organic fluorescent radicals. Overall, our work not only establishes a new synthetic approach toward stable Chichibabin's hydrocarbons but also paves the way for designing NIR emissive open-shell materials with both fundamental understanding and feasible control of their luminescent properties.

Symmetry-Breaking Charge Transfer in Metal-Organic Frameworks.

High quantum-yield charge carrier generation from the initially prepared excitons defines a key step in the light-harvesting and conversion scheme. Photoinduced charge transfer in molecular electron donor-acceptor assemblies is driven by a sizable ΔG0, which compromises the potential of the generated carriers. Reminiscent of the special pair at the reaction center of the natural light-harvesting complex, symmetry-breaking charge transfer (SBCT) within a pair of identical struts of metal-organic framework (MOF) will facilitate the efficient generation of long-lived charge carriers with maximized potentials without incorporating any foreign redox species. We report SBCT in pyrene-based zirconium metal-organic framework (MOF) NU-1000 that leads to efficient generation of radical ions in a polar solvent and bound CT states in a low-polar solvent. The probe unveils the role of the low-lying non-Franck-Condon excitonic states as intermediates in the formation of the SBCT state from the initially prepared Franck-Condon S1 states. Ultrafast and transient spectroscopy─probed over 200 fs-30 μs time scale─evinces a kSBCT = (110 ps)-1 in polar media (εs = 37.5) forming solvated radical ions with recombination rate kCR = (∼45 ns)-1. A slower rate with kSBCT = (203 ps)-1 was recorded in low-polar (εs = 7.0) solvent manifesting a bound [TBAPy•+ TBAPy•-] state with kCR ≈ (17 μs)-1. This discovery, along with other unique photophysical features relevant to light harvesting, should define a MOF-based platform for developing heterogeneous artificial photon energy conversion systems.

Controlling the symmetry breaking charge transfer extent in excited quadrupolar molecules by tuning the locally excited state.

The effect of a locally excited state on charge transfer symmetry breaking (SBCT) in excited quadrupolar molecules in solutions has been studied. The interaction of a locally excited state and two zwitterionic states is found to either increase or decrease the degree of SBCT depending on the molecular parameters. A strategy on how to adjust the molecular parameters to control the extent of SBCT is presented. The influence of level degeneracy on SBCT is identified and discussed in detail. The level degeneracy is shown to lead to the existence of a hidden dipole moment in excited quadrupolar molecules. Its manifestations in SBCT are analyzed. The main conclusions are consistent with the available experimental data.

Red-light operable photosensitizer with symmetry-breaking charge transfer induced intersystem crossing for polymerization of methyl methacrylate.

We present a red light-activated zincII bis(dipyrrin) symmetry breaking charge transfer (SBCT) architecture, showing a large molar absorption coefficient (ε = 15.4 × 104 M-1 cm-1), high reactive singlet oxygen generation efficiency (ΦΔ ≈ 0.8) and long-lived triplet state (τT = 150 μs) compared to the donor-acceptor analogue dipyrrin-BF2 complex, highlighting the superiority of the SBCT approach. For the first time, we demonstrated the potential of a SBCT scaffold in red-light-induced methyl methacrylate (MMA) polymerization, using a dual photocatalyst excitation approach.

Symmetry breaking charge transfer leading to charge separation in a far-red absorbing bisstyryl-BODIPY dimer.

Symmetry breaking charge transfer is one of the important photo-events occurring in photosynthetic reaction centers that is responsible for initiating electron transfer leading to a long-lived charge-separated state and has been successfully employed in light-to-electricity converting optoelectronic devices. In the present study, we report a newly synthesized, far-red absorbing and emitting BODIPY-dimer to undergo symmetry-breaking charge transfer leading to charge-separated states of appreciable lifetimes in polar solvents. Compared to its monomer analog, both steady-state and time-resolved fluorescence originating from the S1 state of the dimer revealed quenching which increased with an increase in solvent polarity. The electrostatic potential map from DFT and the time-dependent DFT calculations suggested the existence of a quadrupolar type charge transfer state in polar solvents, and the singlet excited state to be involved in the charge separation process. The electrochemically determined redox gap being smaller than the energy of the S1 state supported the thermodynamic feasibility of the envisioned symmetry-breaking charge transfer and separation. The spectrum of the charge-separated state arrived from spectroelectrochemical studies, revealing diagnostic peaks helpful for transient spectral interpretation. Finally, ultrafast transient pump-probe spectroscopy provided conclusive evidence of diabatic charge separation in polar solvents by far-red pulsed laser light irradiation. The measured lifetime of the final charge-separated states was found to be 165 ps in dichlorobenzene, 140 ps in benzonitrile, and 43 ps in dimethyl sulfoxide, revealing their significance in light energy harvesting, especially from the less-explored far-red region.

Symmetry breaking charge transfer behaviour in D-A-D triad system by selective excitation

Multichromophoric D-A-D triads synthesized using perylenediimde (PDI) bonded with naphthalenediimide (NDI) units via aliphatic (Triad 1) or aromatic (Triad 2) linker is studied for symmetry breaking charge separation (SB-CS) by selective excitation of the NDI/PDI chromophores. NDI chromophore on excitation transfers electron to PDI chromophore and type of linker played crucial role in stability of generated CS state. Photoluminescence, time resolved fluorescense and transient absorption spectroscopy tools have been used to study the phenomenon. The optical as well as electrochemical study confirmed intramolecular electron transfer from NDI to PDI chromophore. Stable SB-CS state formation is directly resulted in increased open circuit voltage (Voc) of Triad 2 based organic solar cell devices. The selective excitation of chromophoric center and SB-CS in D-A-D type triad is the demand of present electronic device for the formation of long lived charge carrier.

Tuning Symmetry‐Breaking Charge Transfer by Altering Connectivity Between Anthracene Chromophores

AbstractIn this study, we report on the dynamics of symmetry‐breaking charge transfer (SB‐CT) in a specific derivative of bianthracene, 9,9’,10,10’‐tetraphenyl‐2,2’‐bianthracene (TPBA). Unlike the conventional 9,9’‐bianthracene, TPBA exhibits a notably planar structure due to reduced steric hindrance between anthracene chromophores. This structural characteristic results in a pronounced short‐range charge transfer coupling, driven by substantial overlap integrals of hole and electron. This is in contrast to the 9,9’‐bianthracene case, where long‐range Coulombic coupling dominates while minimizing short‐range interactions. Consequently, TPBA reveals an adiabatic mixture between locally‐excited and charge‐transfer diabats, where the extent of their contributions is modulated by the dielectric properties of the surrounding environment. Furthermore, our investigation reveals that the SB‐CT reaction in TPBA is mainly influenced by solvation dynamics, akin to other molecules displaying SB‐CT. Additionally, the dynamics of triplet formation in TPBA vary depending on the solvent polarity. These findings underscore the significance of chromophore connectivity in efficiently manipulating excited‐state potential energy landscapes.

Symmetry-breaking charge-transfer enables turn-on fluorescence sensing in the shortwave infrared spectral region for in vivo vasculature redox homeostasis

Functional in vivo imaging in the short-wavelength infrared spectral region (SWIR) has broad potential in disease diagnosis, fluorescence guided surgery and in vivo pharmacology. In recent years, dyes absorbing in the SWIR region started to emerge. Yet, probe design based on these SWIR dyes remains difficult due to scarcity of efficient fluorescence quenching mechanism. Here, we propose that symmetry breaking charge transfer is a viable approach to develop off-on type probes with SWIR fluorophores. We synthesized the first V-shaped asymmetric cyanine dimer (VAD1080) and verified that its fluorescence was efficiently quenched. The subsequent treatment with highly oxidative species including ONOO- could be employed to inhibit this photophysical quenching mechanism and restore the fluorescence. Its fluorescence sensing capability of oxidative stress in vivo was exemplified. We discovered that overdose of APAP induced a rapid rise of oxidative stress in the vasculature prior to a prior in the liver. This yields insights over the toxicology of APAP and suggested that clearance of reactive species in blood vessels is be a viable approach as a therapeutic measure of acute APAP toxicity.

Engineering Exciton Dynamics with Synthetic DNA Scaffolds.

ConspectusExcitons are the molecular-scale currency of electronic energy. Control over excitons enables energy to be directed and harnessed for light harvesting, electronics, and sensing. Excitonic circuits achieve such control by arranging electronically active molecules to prescribe desired spatiotemporal dynamics. Photosynthetic solar energy conversion is a canonical example of the power of excitonic circuits, where chromophores are positioned in a protein scaffold to perform efficient light capture, energy transport, and charge separation. Synthetic systems that aim to emulate this functionality include self-assembled aggregates, molecular crystals, and chromophore-modified proteins. While the potential of this approach is clear, these systems lack the structural precision to control excitons or even test the limits of their power. In recent years, DNA origami has emerged as a designer material that exploits biological building blocks to construct nanoscale architectures. The structural precision afforded by DNA origami has enabled the pursuit of naturally inspired organizational principles in a highly precise and scalable manner. In this Account, we describe recent developments in DNA-based platforms that spatially organize chromophores to construct tunable excitonic systems. The high fidelity of DNA base pairing enables the formation of programmable nanoscale architectures, and sequence-specific placement allows for the precise positioning of chromophores within the DNA structure. The integration of a wide range of chromophores across the visible spectrum introduces spectral tunability. These excitonic DNA-chromophore assemblies not only serve as model systems for light harvesting, solar conversion, and sensing but also lay the groundwork for the integration of coupled chromophores into larger-scale nucleic acid architectures.We have used this approach to generate DNA-chromophore assemblies of strongly coupled delocalized excited states through both sequence-specific self-assembly and the covalent attachment of chromophores. These strategies have been leveraged to independently control excitonic coupling and system-bath interaction, which together control energy transfer. We then extended this framework to identify how scaffold configurations can steer the formation of symmetry-breaking charge transfer states, paving the way toward the design of dual light-harvesting and charge separation DNA machinery. In an orthogonal application, we used the programmability of DNA chromophore assemblies to change the optical emission properties of strongly coupled dimers, generating a series of fluorophore-modified constructs with separable emission properties for fluorescence assays. Upcoming advances in the chemical modification of nucleotides, design of large-scale DNA origami, and predictive computational methods will aid in constructing excitonic assemblies for optical and computing applications. Collectively, the development of DNA-chromophore assemblies as a platform for excitonic circuitry offers a pathway to identifying and applying design principles for light harvesting and molecular electronics.

Symmetry-breaking charge transfer in an excited acridine-dione derivative: Effects of hydrogen bonding, clustering, and cooperativity in mixtures of methanol and dimethylformamide

A theory of fluorescence quenching of photoexcited centrosymmetric acridine-dione derivative induced by H-bonding interactions with solvent in mixtures of methanol (MeOH) and N,N-dimethylformamide (DMF) is developed. The theory takes into account both dynamic and static mechanisms of the quenching. An unusual threshold-type dependence of the quenching efficiency on the concentration of methanol in the mixture observed earlier in experiment is analyzed theoretically under the following assumptions: (i) individual MeOH molecules and their short hydrogen-bonded clusters form weak complexes with the dye in solution and these interactions do not affect fluorescence kinetics significantly, (ii) long clusters form strongly bound complexes with the dye and thus induce symmetry-breaking intramolecular charge transfer and efficient quenching of fluorescence. These assumptions are consistent with the cooperative character of H-bonding in alcohols and allow one to explain the observed absence of quenching at MeOH concentrations below ∼9 M. A model of H-bond clustering in mixtures of alcohols and H-bond-accepting solvents is developed. The suggested approach gives a quantitative description of the observed concentration dependence of the fluorescence yield and well reproduces the non-exponential kinetics of the fluorescence decay measured in experiments. Since the degree of the charge transfer dissymmetry in these processes is sensitive to interactions between the dye and solvent, new possibilities emerge for experimental studies on details of H-bond clustering in protic solvents.

The effect of energy level degeneracy on symmetry-breaking charge transfer: Excited octupolar dyes.

A three-level model of symmetry-breaking charge transfer (SBCT) in excited octupolar molecules is developed. The model describes the joint dynamics of the solvent and the dye in the excited state. For this, a distribution function in the space of two reaction coordinates is introduced. An evolution equation of this function is derived. A strict definition of the reaction coordinates is given, and its dynamic characteristics are determined. The free energy surface in the space of these coordinates is calculated. To quantify the symmetry-breaking degree, a two-dimensional dissymmetry vector is introduced. The model predicts the absence of SBCT in apolar solvents and an abrupt increase in its degree to half the maximum value in weakly polar solvents. The dye dipole moment is revealed to be directed along a molecular arm independently of the direction and the strength of the electric field of the solvent created by its orientational polarization. The conditions for the occurrence and nature of this effect are discussed. The effect of the degeneracy of excited states, which is inherent in octupolar dyes in the excited state, on SBCT is revealed. Degeneracy of energy levels is shown to lead to a significant increase in the symmetry-breaking degree. The effect of SBCT on the dependence of the Stokes on the solvent polarity is calculated and compared with the available experimental data.

Aromatic-bridged and meso-meso-linked BF2-smaragdyrin dimers exhibit fast decays in polar solvents by symmetry-breaking charge transfer

Symmetry-breaking charge transfer is one of the key process in photosynthetic reaction centers and specific artificial optoelectronic devices such as dye-sensitized solar cells. Here we report the synthesis of aromatic-bridged BF2-smaragdyrin dimers, meso-free BF2-smaragdyrin, and its meso-meso-linked BF2-smaragdyrin dimer. The decays of S1-states of these dimers are accelerated with an increase in solvent polarity and a decrease in the distance between the two BF2-smaragdyrin units, suggesting symmetry-breaking charge transfer. The fluorescence lifetimes of the dimers become shortened in polar solvents. However, ultrafast transient absorption spectroscopy do not detect charge-separated ion pairs. On the basis of these results, we conclude that the decays of the excited states of the BF2-smaragdyrin dimers are accelerated by solvation-induced symmetry-breaking charge transfer, depending on the degree of the electronic interaction between the smaragdryin units as a rare case for porphyrinoids. The degree of charge transfer is larger for dimers with larger electronic interactions.

Symmetry-breaking charge transfer and intersystem crossing in copper phthalocyanine thin films.

Intermolecular interactions in π-stacked chromophores strongly influence their photophysical properties, and thereby also their function in photonic applications. Mixed electronic and vibrational coupling interactions lead to complex potential energy landscapes with competitive photophysical pathways. Here, we characterize the photoexcited dynamics of the small molecule semiconductor copper pthalocyanine (CuPc) in solution and in thin film, the latter comprising two different π-stacked architectures, α-CuPc and β-CuPc. In solution, CuPc undergoes ultrafast intersytem crossing (ISC) to the triplet excited state. In the solid state, both α-CuPc and β-CuPc morphologies exhibit a mixing between Frenkel and charge-transfer excitons (Frenkel-CT mixing). We find that this mixing influences the photophysical properties differently, based on morphology. In addition to ISC, α-CuPc demonstrates symmetry-breaking charge transfer, which furthermore depends on excitation wavelength. This mechanism is not observed in β-CuPc. These results elucidate how molecular organization mediates the balance of competitive photexcited decay mechanisms in organic semiconductors.

On the Cooperative Origin of Solvent-Enhanced Symmetry-Breaking Charge Transfer in a Covalently Bound Tetracene Dimer Leading to Singlet Fission.

Singlet fission in covalently bound acene dimers in solution is driven by the interplay of excitonic and singlet correlated triplet 1(TT) states with intermediate charge-transfer states, a process which depends sensitively on the solvent environment. We use high-level electronic structure methods to explore this singlet fission process in a linked tetracene dimer, with emphasis on the symmetry-breaking mechanism for the charge-transfer (CT) states induced by low-frequency antisymmetric vibrations and polar/polarizable solvents. A combination of the second-order algebraic diagrammatic construction (ADC(2)) and density functional theory/multireference configuration interaction (DFT/MRCI) methods are employed, along with a state-specific conductor-like screening model (COSMO) solvation model in the former case. This work quantifies, for the first time, an earlier mechanistic proposal [Alvertis et al., J. Am. Chem. Soc. 2019, 141, 17558] according to which solvent-induced symmetry breaking leads to a high-energy CT state which interacts with the correlated triplet state, resulting in singlet fission. An approximate assessment of the nonadiabatic interactions between the different electronic states underscores that the CT states are essential in facilitating the transition from the bright excitonic state to the 1(TT) state leading to singlet fission. We show that several types of symmetry-breaking inter- and intra-fragment vibrations play a crucial role in a concerted mechanism with the solvent environment and with the symmetric inter-fragment torsion, which tunes the admixture of excitonic and CT states. This offers a new perspective on how solvent-induced symmetry-breaking CT can be understood and how it cooperates with intramolecular mechanisms in singlet fission.

Symmetry Breaking Charge Transfer in DNA-Templated Perylene Dimer Aggregates.

Molecular aggregates are of interest to a broad range of fields including light harvesting, organic optoelectronics, and nanoscale computing. In molecular aggregates, nonradiative decay pathways may emerge that were not present in the constituent molecules. Such nonradiative decay pathways may include singlet fission, excimer relaxation, and symmetry-breaking charge transfer. Singlet fission, sometimes referred to as excitation multiplication, is of great interest to the fields of energy conversion and quantum information. For example, endothermic singlet fission, which avoids energy loss, has been observed in covalently bound, linear perylene trimers and tetramers. In this work, the electronic structure and excited-state dynamics of dimers of a perylene derivative templated using DNA were investigated. Specifically, DNA Holliday junctions were used to template the aggregation of two perylene molecules covalently linked to a modified uracil nucleobase through an ethynyl group. The perylenes were templated in the form of monomer, transverse dimer, and adjacent dimer configurations. The electronic structure of the perylene monomers and dimers were characterized via steady-state absorption and fluorescence spectroscopy. Initial insights into their excited-state dynamics were gleaned from relative fluorescence intensity measurements, which indicated that a new nonradiative decay pathway emerges in the dimers. Femtosecond visible transient absorption spectroscopy was subsequently used to elucidate the excited-state dynamics. A new excited-state absorption feature grows in on the tens of picosecond timescale in the dimers, which is attributed to the formation of perylene anions and cations resulting from symmetry-breaking charge transfer. Given the close proximity required for symmetry-breaking charge transfer, the results shed promising light on the prospect of singlet fission in DNA-templated molecular aggregates.

Charge Separation and Intersystem Crossing in Homo- and Hetero-Compact Naphthalimide Dimers.

Naphthalimide (NI) homo- and hetero-dimers adopting orthogonal geometry were prepared to study photo-induced symmetry-breaking charge transfer (SBCT) and charge recombination (CR)-induced intersystem crossing (ISC). The two moieties in the dimer are connected either at the 3-C or 4-C position of the NI unit. The photophysical properties of the dimers were studied with steady-state and transient absorption spectroscopic methods. Significant CT only occurs for the hetero-dimer, in which one NI unit has a 4-amino substituent and the other NI unit is without it. The CR-induced ISC is most efficient for this dimer (singlet oxygen quantum yield ΦΔ = 50.3%). For the homo-dimer, in which both NI units did not present amino substitution, SBCT was not observed. Based on the electrochemical studies, we propose that the absence of SBCT for the homo-dimer is attributed to its high oxidation potential and low reduction potential. Femtosecond transient absorption (fs TA) spectra show that there is no charge separation (CS) for the homo-dimer. Nanosecond transient absorption spectroscopy indicate the formation of a triplet state with electron delocalization for the homo dimer, with a lifetime of 72.0 μs, while for the hetero dimer a triplet state with an intrinsic lifetime of 206.4 μs is observed. CS (11.6 ps) and slow CR-induced ISC (>1.5 ns) were observed for the hetero-dimer. Time-resolved electron paramagnetic resonance spectra give the zero-field splitting parameters (|D| = 1894 MHz and |E| = 111 MHz) and electron spin polarization patterns (e, e, e, a, a, a) for the triplet state of the hetero-dimer, inferring that the triplet state of the hetero-dimer is confined on the amino-substituted NI moiety.

Controlling Symmetry Breaking Charge Transfer in BODIPY Pairs.

Symmetry breaking charge transfer (SBCT) is a process in which a pair of identical chromophores absorb a photon and use its energy to transfer an electron from one chromophore to the other, breaking the symmetry of the chromophore pair. This excited state phenomenon is observed in photosynthetic organisms where it enables efficient formation of separated charges that ultimately catalyze biosynthesis. SBCT has also been proposed as a means for developing photovoltaics and photocatalytic systems that operate with minimal energy loss. It is known that SBCT in both biological and artificial systems is in part made possible by the local environment in which it occurs, which can move to stabilize the asymmetric SBCT state. However, how environmental degrees of freedom act in concert with steric and structural constraints placed on a chromophore pair to dictate its ability to generate long-lived charge pairs via SBCT remain open topics of investigation.In this Account, we compare a broad series of dipyrrin dimers that are linked by distinct bridging groups to discern how the spatial separation and mutual orientation of linked chromophores and the structural flexibility of their linker each impact SBCT efficiency. Across this material set, we observe a general trend that SBCT is accelerated as the spatial separation between dimer chromophores decreases, consistent with the expectation that the electronic coupling between these units varies exponentially with their separation. However, one key observation is that the rate of charge recombination following SBCT was found to slow with decreasing interchromophore separation, rather than speed up. This stems from an enhancement of the dimer's structural rigidity due to increasing steric repulsion as the length of their linker shrinks. This rigidity further inhibits charge recombination in systems where symmetry has already enforced zero HOMO-LUMO overlap. Additionally, for the forward transfer, the active torsion is shown to increase LUMO-LUMO coupling, allowing for faster SBCT within bridging groups.By understanding trends for how rates of SBCT and charge recombination depend on a dimer's internal structure and its environment, we identify design guidelines for creating artificial systems for driving sustained light-induced charge separation. Such systems can find application in solar energy technologies and photocatalytic applications and can serve as a model for light-induced charge separation in biological systems.

Efficient symmetry breaking spin–orbit charge transfer-induced intersystem crossing in compact orthogonal perylene-phenothiazine or -phenoxazine triads and observation of the delayed fluorescence

For the first time, efficient spin–orbit charge transfer intersystem crossing (ΦΔ = 70%) is attained via the symmetry-breaking charge transfer approach in newly designed perylene orthogonal triads.

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

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.