Direct Writing of Room Temperature Polariton Condensate Lattice.

Realizing lattices of exciton polariton condensates has been of much interest owing to the potential of such systems to realize analogue Hamiltonian simulators and physical computing architectures. Here, we report the realization of a room temperature polariton condensate lattice using a direct-write approach. Polariton condensation is achieved in a microcavity embedded with host-guest Frenkel excitons of an organic dye (rhodamine) in a small-molecule ionic isolation lattice (SMILES). The microcavity is patterned using focused ion beam etching to realize arbitrary lattice geometries, including defect sites on demand. The band structure of the lattice and the emergence of condensation are imaged using momentum-resolved spectroscopy. The introduction of defect sites is shown to lower the condensation threshold and result in the formation of a defect band in the condensation spectrum. The present approach allows us to study periodic, quasiperiodic, and disordered polariton condensate lattices at room temperature using a direct-write approach.

Insight from Electrochemical Analysis in the Radical Cation State of a Monopyrrolotetrathiafulvalene Based [2]Rotaxane.

Mechanically interlocked molecules are a class of compounds used for controlling directional movement when barriers can be raised and lowered using external stimuli. Applied voltages can turn on redox states to alter electrostatic barriers but their use for directing motion requires knowledge of their impact on the kinetics. Herein, we make the first measurements on the movement of cyclobis(paraquat-p-phenylene) (CBPQT4+) across the radical-cation state of monopyrrolotetrathiafulvalene (MPTTF) in a [2]rotaxane using variable scan-rate electrochemistry. The [2]rotaxane is designed in a way that directs CBPQT4+ to a high-energy co-conformation upon oxidation of MPTTF to either the radical cation (MPTTF•+) or the dication (MPTTF2+). 1H NMR spectroscopic investigations carried out in acetonitrile at 298 K showed direct interconversion to the thermodynamically more stable ground-state co-conformation with CBPQT4+ moving across the oxidized MPTTF2+ electrostatic barrier. The electrochemical studies revealed that interconversion takes place by movement of CBPQT4+ across both the MPTTF•+ (19.3 kcal mol-1) and MPTTF2+ (18.7 kcal mol-1) barriers. The outcome of our studies shows that MPTTF has three accessible redox states that can be used to kinetically control the movement of the ring component in mechanically interlocked molecules.

Breaking Radial Dipole Symmetry in Planar Macrocycles Modulates Edge-to-Edge Packing and Disrupts Cofacial Stacking.

Dipolar interactions are ever-present in supramolecular architectures, though their impact is typically revealed by making dipoles stronger. While it is also possible to assess the role of dipoles by altering their orientations by using synthetic design, doing so without altering the molecular shape is not straightforward. We have now done this by flipping one triazole unit in a rigid macrocycle, tricarb. The macrocycle is composed of three carbazoles (2 Debye) and three triazoles (5 Debye) defining an array of dipoles aligned radially but organized alternately in and out. These dipoles are believed to dictate edge-to-edge tiling and face-to-face stacking. We modified our synthesis to prepare isosteric macrocycles with the orientation of one triazole dipole rotated 40°. The new dipole orientation guides edge-to-edge contacts to reorder the stability of two surface-bound 2D polymorphs. The impact on dipole-enhanced π stacking, however, was unexpected. Our stacking model identified an unchanged set of short-range (3.4 Å) anti-parallel dipole contacts. Despite this situation, the reduction in self-association was attributed to long-range (~6.4 Å) dipolar repulsions between π-stacked macrocycles. This work highlights our ability to control the build-up and symmetry of macrocyclic skeletons by synthetic design, and the work needed to further our understanding of how dipoles control self-assembly.

Cone Angles Quantify and Predict Affinity and Reactivity of Anion Complexes between Trifluoroborates and Rigid Macrocycles.

Steric manipulation is a known concept in molecular recognition but there is currently no linear free energy relationship correlating sterics to the stability of receptor-anion complexes nor to the reactivity of the bound anion. By analogy to Tolman cone angles in cation coordination chemistry, we explore how to define and correlate cone angles of organo-trifluoroborates (R-BF3-) to the affinities observed for cyanostar-anion binding. We extend the analogy to a rare investigation of reactivity and how it changes upon anion binding. The substituent on the anion is used to define the cone angle, θ. A series of 10 anions were studied including versions with ethynyl, ethylene, and ethyl substituents that were selected to tune steric bulk across the sp, sp2 and sp3 hybridized a-carbons bearing 0, 1 and 2 hydrogen atoms. A linear relationship between affinity and cone angle is observed for anions bearing substituents larger than the -BF3- headgroup. This correlation predicted affinities of two new anions to within ±5%. We explored how complexation affects the reactivity of fluoride exchange. The yield of fluoride transfer from R-BF3- to Lewis acid triphenylborane is correlated with cone angle. We predict that other rigid macrocycles, like commercially available bambusuril, could follow these trends.

Boosting the Brightness of Raman Tags Using Cyanostar Macrocycles.

Raman probes have received growing attention for their potential use in super-multiplex biological imaging and flow cytometry applications that cannot be achieved using fluorescent probes. However, obtaining strong Raman scattering signals from small Raman probes has posed a challenge that holds back their practical implementation. Here, we present new types of Raman-active nanoparticles (Rdots) that incorporate ionophore macrocycles, known as cyanostars, to act as ion-driven and structure-directing spacers to address this problem. These macrocycle-enhanced Rdots (MERdots) exhibit sharper and higher electronic absorption peaks than Rdots. When combined with resonant broadband time-domain Raman spectroscopy, these MERdots show a ∼3-fold increase in Raman intensity compared to conventional Rdots under the same particle concentration. Additionally, the detection limit on the concentration of MERdots is improved by a factor of 2.5 compared to that of Rdots and a factor of 430 compared to that of Raman dye molecules in solution. The compact size of MERdots (26 nm in diameter) and their increased Raman signal intensity, along with the broadband capabilities of time-domain resonant Raman spectroscopy, make them promising candidates for a wide range of biological applications.

Steric Control over the Threading of Pyrophosphonates with One or Two Cyanostar Macrocycles during Pseudorotaxane Formation.

The supramolecular recognition of anions is increasingly harnessed to achieve the self-assembly of supramolecular architectures, ranging from cages and polymers to (pseudo)rotaxanes. The cyanostar (CS) macrocycle has previously been shown to form 2 : 1 complexes with organophosphate anions that can be turned into [3]rotaxanes by stoppering. Here we achieved steric control over the assembly of pseudorotaxanes comprising the cyanostar macrocycle and a thread that is based, for the first time, on organo-pyrophosphonates. Subtle differences in steric bulk on the threads allowed formation of either [3]pseudorotaxanes or [2]pseudorotaxanes. We demonstrate that the threading kinetics are governed by the steric demand of the organo-pyrophosphonates and in one case, slows down to the timescale of minutes. Calculations show that the dianions are sterically offset inside the macrocycles. Our findings broaden the scope of cyanostar-anion assemblies and may have relevance for the design of molecular machines whose directionality is a result of relatively slow slipping.

Solvent Acts as the Referee in a Match-Up Between Charged and Preorganized Receptors.

The prevalence of anion-cation contacts in biomolecular recognition under aqueous conditions suggests that ionic interactions should dominate the binding of anions in solvents across both high and low polarities. Investigations of this idea using titrations in low polarity solvents are impaired by interferences from ion pairing that prevent a clear picture of binding. To address this limitation and test the impact of ion-ion interactions across multiple solvents, we quantified chloride binding to a cationic receptor after accounting for ion pairing. In these studies, we created a chelate receptor using aryl-triazole CH donors and a quinolinium unit that directs its cationic methyl inside the binding pocket. In low-polarity dichloromethane, the 1 : 1 complex (log K1 : 1 ~ 7.3) is more stable than neutral chelates, but fortuitously comparable to a preorganized macrocycle (log K1 : 1 ~ 6.9). Polar acetonitrile and DMSO diminish stabilities of the charged receptor (log K1 : 1 ~ 3.7 and 1.9) but surprisingly 100-fold more than the macrocycle. While both receptors lose stability by dielectric screening of electrostatic stability, the cationic receptor also pays additional costs of organization. Thus even though the charged receptor has stronger binding in apolar solvents, the uncharged receptor has more anion affinity in polar solvents.

Cooperativity in Photofoldamer Chloride Double Helices Turned On with Sequences and Solvents, Around with Guests, and Off with Light.

Photofoldamers are sequence-defined receptors capable of switching guest binding on and off. When two foldamer strands wrap around the guest into 2:1 double helical complexes, cooperativity emerges, and with it comes the possibility to switch cooperativity with light and other stimuli. We use lessons from nonswitchable sequence isomers of aryl-triazole foldamers to guide how to vary the sequence location of azobenzenes from the end (FEND) to the interior (FIN) and report their impact on the cooperative formation of 2:1 complexes with Cl-. This sequence change produces a 125-fold increase from anti-cooperative (α = 0.008) for FEND to non-cooperative with FIN (α = 1.0). Density functional theory (DFT) studies show greater H-bonding and a more relaxed double helix for FIN. The solvent and guest complement the synthetic designs. Use of acetonitrile to enhance solvophobicity further enhances cooperativity in FIN (α = 126) but lowers the difference in cooperativity between sequences. Surprisingly, the impact of the sequence on cooperativity is inverted when the guest size is increased from Cl- (3.4 Å) to BF4- (4.1 Å). While photoconversion of interior azobenzenes was poor, the cis-cis isomer forms 1:1 complexes around chloride consistent with switching cooperativity. The effect of the guest, solvent, and light on the double-helix cooperativity depends on the sequence.

Triplet States of Cyanostar and Its Anion Complexes.

The design of advanced optical materials based on triplet states requires knowledge of the triplet energies of the molecular building blocks. To this end, we report the triplet energy of cyanostar (CS) macrocycles, which are the key structure-directing units of small-molecule ionic isolation lattices (SMILES) that have emerged as programmable optical materials. Cyanostar is a cyclic pentamer of covalently linked cyanostilbene units that form π-stacked dimers when binding anions as 2:1 complexes. The triplet energies, ET, of the parent cyanostar and its 2:1 complex around PF6- are measured to be 1.96 and 2.02 eV, respectively, using phosphorescence quenching studies at room temperature. The similarity of these triplet energies suggests that anion complexation leaves the triplet energy relatively unchanged. Similar energies (2.0 and 1.98 eV, respectively) were also obtained from phosphorescence spectra of the iodinated form, I-CS, and of complexes formed with PF6- and IO4- recorded at 85 K in an organic glass. Thus, measures of the triplet energies likely reflect geometries close to those of the ground state either directly by triplet energy transfer to the ground state or indirectly by using frozen media to inhibit relaxation. Density functional theory (DFT) and time-dependent DFT were undertaken on a cyanostar analogue, CSH, to examine the triplet state. The triplet excitation localizes on a single olefin whether in the single cyanostar or its π-stacked dimer. Restriction of the geometrical changes by forming either a dimer of macrocycles, (CSH)2, or a complex, (CSH)2·PF6-, reduces the relaxation resulting in an adiabatic energy of the triplet state of 2.0 eV. This structural constraint is also expected for solid-state SMILES materials. The obtained T1 energy of 2.0 eV is a key guide line for the design of SMILES materials for the manipulation of triplet excitons by triplet state engineering in the future.

Universal Concept for Bright, Organic, Solid-State Emitters─Doping of Small-Molecule Ionic Isolation Lattices with FRET Acceptors.

Brightly fluorescent solid-state materials are highly desirable for bioimaging, optoelectronic applications, and energy harvesting. However, the close contact between π-systems most often leads to quenching. Recently, we developed small-molecule ionic isolation lattices (SMILES) that efficiently isolate fluorophores while ensuring very high densities of the dyes. Nevertheless, efficient Förster resonance energy transfer (FRET) energy migration in such dense systems is inevitable. While attractive for energy harvesting applications, FRET also significantly compromises quantum yields of fluorescent solids by funneling the excitation energy to dark trap states. Here, we investigate the underlying property of FRET and exploit it to our favor by intentionally introducing fluorescent dopants into SMILES materials, acting as FRET acceptors with favorable photophysical properties. This doping is shown to outcompete energy migration to dark trap states while also ruling out reabsorption effects in dense SMILES materials, resulting in universal fluorescent solid-state materials (thin films, powders, and crystals) with superior properties. These include emission quantum yields reaching as high as 50-65%, programmable fluorescence lifetimes with mono-exponential decay, and independent selection of absorption and emission maxima. The volume normalized brightness of these FRET-based SMILES now reach values up to 32,200 M-1 cm-1 nm-3 and can deliver freely tunable spectroscopic properties for the fabrication of super-bright advanced optical materials. It is found that SMILES prohibit PET quenching between donor and acceptor dyes that is observed for non-SMILES mixtures of the same dyes. This allows a very broad selection of donor and acceptor dyes for use in FRET SMILES.

Revealing the Hidden Costs of Organization in Host-Guest Chemistry Using Chloride-Binding Foldamers and Their Solvent Dependence.

Preorganization is a key concept in supramolecular chemistry. Preorganized receptors enhance binding by minimizing the organization costs associated with adopting the conformation needed to orient the binding sites toward the guest. Conversely, poorly organized receptors show affinities below what is possible based on the potential of their specific binding interactions. Despite the fact that the organization energy is paid each time like a tax, its value has never been measured directly, though many compounds have been developed to measure its effects. We present a method to quantify the hidden costs of receptor organization by independently measuring the contribution it makes to chloride complexation by a flexible foldameric receptor. This method uses folding energy to approximate organization energy and relies on measurement of the coil-helix equilibrium as a function of solvent. We also rely on the finding, established with rigid receptors, that affinity is inversely related to the solvent dielectric and expect the same for the foldamer's helically organized state. Increasing solvent polarity across nine dichloromethane-acetonitrile mixtures we see an unusual V-shape in affinity (decrease then increase). Quantitatively, this shape arises from weakened hydrogen-bonding interactions with solvent polarity followed by solvent-driven folding into an organized helix. We confirm that dielectric screening impacts the stability of host-guest complexes of flexible foldamers just like rigid receptors. These results experimentally verify the canonical model of binding (affinity depends on the sum of organization and noncovalent interactions). The picture of how solvent impacts complex stability and conformational organization thereby helps lay the groundwork for de novo receptor design.

High-fidelity Recognition of Organotrifluoroborate Anions (R-BF3 - ) as Designer Guest Molecules.

The recognition of boron compounds is well developed as boronic acids but untapped as organotrifluoroborate anions (R-BF3 - ). We are exploring the development of these and other designer anions as anion-recognition motifs by considering them as substituted versions of the parent inorganic ion. To this end, we demonstrate strong and reliable binding of organic trifluoroborates, R-BF3 - , by cyanostar macrocycles that are size-complementary to the inorganic BF4 - progenitors. We find that recognition is modulated by the substituent's sterics and that the affinities are retained using the common K+ salts of R-BF3 - anions.

Quantifying the barrier for the movement of cyclobis(paraquat-p-phenylene) over the dication of monopyrrolotetrathiafulvalene.

A bistable [2]pseudorotaxane 1⊂CBPQT·4PF6 and a bistable [2]rotaxane 2·4PF6 have been synthesised to measure the height of an electrostatic barrier produced by double molecular oxidation (0 to +2). Both systems have monopyrrolotetrathiafulvalene (MPTTF) and oxyphenylene (OP) as stations for cyclobis(paraquat-p-phenylene) (CBPQT4+). They have a large stopper at one end while the second stopper in 24+ is composed of a thioethyl (SEt) group and a thiodiethyleneglycol (TDEG) substituent, whereas in 1⊂CBPQT4+, the SEt group has been replaced with a less bulky thiomethyl (SMe) group. This seemingly small difference in the substituents on the MPTTF unit leads to profound changes when comparing the physical properties of the two systems allowing for the first measurement of the deslipping of the CBPQT4+ ring over an MPTTF2+ unit in the [2]pseudorotaxane. Cyclic voltammetry and 1H NMR spectroscopy were used to investigate the switching mechanism for 1⊂CBPQT·MPTTF4+ and 2·MPTTF4+, and it was found that CBPQT4+ moves first to the OP station producing 1⊂CBPQT·OP6+ and 2·OP6+, respectively, upon oxidation of the MPTTF unit. The kinetics of the complexation/decomplexation process occurring in 1⊂CBPQT·MPTTF4+ and in 1⊂CBPQT·OP6+ were studied, allowing the free energy of the transition state when CBPQT4+ moves across a neutral MPTTF unit (17.0 kcal mol-1) or a di-oxidised MPTTF2+ unit (24.0 kcal mol-1) to be determined. These results demonstrate that oxidation of the MPTTF unit to MPTTF2+ increases the energy barrier that the CBPQT4+ ring must overcome for decomplexation to occur by 7.0 kcal mol-1.

Polarity-Tolerant Chloride Binding in Foldamer Capsules by Programmed Solvent-Exclusion.

Persistent anion binding in a wide range of solution environments is a key challenge that continues to motivate and demand new strategies in synthetic receptor design. Though strong binding in low-polarity solvents has become routine, our ability to maintain high affinities in high-polarity solvents has not yet reached the standard set by nature. Anions are bound and transported regularly in aqueous environments by proteins that use secondary and tertiary structure to isolate anion binding sites from water. Inspired by this principle of solvent exclusion, we created a sequence-defined foldameric capsule whose global minimum conformation displays a helical folded state and is preorganized for 1:1 anion complexation. The high stability of the folded geometry and its ability to exclude solvent were supported by solid-state and solution phase studies. This capsule then withstood a 4-fold increase in solvent dielectric constant (εr) from dichloromethane (9) to acetonitrile (36) while maintaining a high and solvent-independent affinity of 105 M-1; ΔG ∼ 28 kJ mol-1. This behavior is unusual. More typical of solvent-dependent behavior, Cl- affinities were seen to plummet in control compounds, such as aryl-triazole macrocycles and pentads, with their solvent-exposed binding cavities susceptible to dielectric screening. Finally, dimethyl sulfoxide denatures the foldamer by putative solvent binding, which then lowers the foldamer's Cl- affinity to normal levels. The design of this capsule demonstrates a new prototype for the development of potent receptors that can operate in polar solvents and has the potential to help manage hydrophilic anions present in the hydrosphere and biosphere.

Anion-Selective Electrodes Based On a CH-Hydrogen Bonding Bis-macrocyclic Ionophore with a Clamshell Architecture.

CH-hydrogen bonding provides access to new building blocks for making macrocyclic ionophores with high degrees of preorganization and selective anion recognition. In this study, an anion-binding ionophore in the shape of a clamshell (ClS) was employed that is composed of two cyanostar (CNstar) macrocycles with preorganized cavities linked with a 12-carbon chain. This ionophore allows for anion complexation by CH-hydrogen bonding. The potentiometric performance of membrane-based ion-selective electrodes incorporating this ionophore was evaluated. Different membrane compositions were prepared to determine the optimum concentrations of the ionophore and lipophilic additive in the membrane. The optimized electrode had a slope of -58.2 mV/decade and demonstrated an anti-Hofmeister selectivity pattern toward iodide with a nanomolar detection limit. Electrospray ionization mass spectrometry was employed to study the relative association strengths of ClS with various anions. The observed mass peaks of the ion-ionophore complexes were found to be consistent with the potentiometric selectivity pattern of the corresponding electrodes. Overall, the selectivity of the electrode could be altered by using an ionophore in which the two CNstar macrocycles are linked together with a flexible 12-carbon chain to control the molecularity of the binding event.

Chain Entropy Beats Hydrogen Bonds to Unfold and Thread Dialcohol Phosphates inside Cyanostar Macrocycles To Form [3]Pseudorotaxanes.

The recognition of substituted phosphates underpins many processes including DNA binding, enantioselective catalysis, and recently template-directed rotaxane synthesis. Beyond ATP and a few commercial substrates, however, little is known about how substituents effect organophosphate recognition. Here, we examined alcohol substituents and their impact on recognition by cyanostar macrocycles. The organophosphates were disubstituted by alcohols of various chain lengths, dipropanol, dihexanol, and didecanol phosphate, each accessed using modular solid-phases syntheses. Based on the known size-selective binding of phosphates by π-stacked dimers of cyanostars, threaded [3]pseudorotaxanes were anticipated. While seen with butyl substituents, pseudorotaxane formation was disrupted by competitive OH···O- hydrogen bonding between both terminal hydroxyls and the anionic phosphate unit. Crystallography also showed formation of a backfolded propanol conformation resulting in an 8-membered ring and a perched cyanostar assembly. Motivated by established entropic penalties accompanying ring formation, we reinstated [3]pseudorotaxanes by extending the size of the substituent to hexanol and decanol. Chain entropy overcomes the enthalpically favored OH···O- contacts to favor random-coil conformations required for seamless, high-fidelity threading of dihexanol and didecanol phosphates inside cyanostars. These studies highlight how chain length and functional groups on phosphate's substituents can be powerful design tools to regulate binding and control assembly formation during phosphate recognition.

Inchworm movement of two rings switching onto a thread by biased Brownian diffusion represent a three-body problem.

The coordinated motion of many individual components underpins the operation of all machines. However, despite generations of experience in engineering, understanding the motion of three or more coupled components remains a challenge, known since the time of Newton as the "three-body problem." Here, we describe, quantify, and simulate a molecular three-body problem of threading two molecular rings onto a linear molecular thread. Specifically, we use voltage-triggered reduction of a tetrazine-based thread to capture two cyanostar macrocycles and form a [3]pseudorotaxane product. As a consequence of the noncovalent coupling between the cyanostar rings, we find the threading occurs by an unexpected and rare inchworm-like motion where one ring follows the other. The mechanism was derived from controls, analysis of cyclic voltammetry (CV) traces, and Brownian dynamics simulations. CVs from two noncovalently interacting rings match that of two covalently linked rings designed to thread via the inchworm pathway, and they deviate considerably from the CV of a macrocycle designed to thread via a stepwise pathway. Time-dependent electrochemistry provides estimates of rate constants for threading. Experimentally derived parameters (energy wells, barriers, diffusion coefficients) helped determine likely pathways of motion with rate-kinetics and Brownian dynamics simulations. Simulations verified intercomponent coupling could be separated into ring-thread interactions for kinetics, and ring-ring interactions for thermodynamics to reduce the three-body problem to a two-body one. Our findings provide a basis for high-throughput design of molecular machinery with multiple components undergoing coupled motion.

Recognition and applications of anion-anion dimers based on anti-electrostatic hydrogen bonds (AEHBs).

Based on Coulomb's Law alone, electrostatic repulsion between two anions is expected to prevent their dimerization. Contrary to that idea, this Tutorial Review will present evidence showing that anion-anion dimers of protic hydroxyanions can form readily, and describe conditions that facilitate their formation. From X-ray crystal structures, we learn that hydroxyanions dimerize and oligomerize by overcoming long-range electrostatic opposition. Common examples are hydroxyanions of phosphate, sulfate, and carbonate, often in partnership with charged and neutral receptors. Short-range hydrogen bonds between anionic donors and acceptors are defined as anti-electrostatic hydrogen bonds (AEHBs) with insight from theoretical studies. While anion dimers are difficult to identify unequivocally in solution, these solution dimers have recently been definitively identified. The development of the supramolecular chemistry of anion-anion dimers has led to applications in hierarchical assemblies, such as supramolecular polymers and hydrogen bonded organic frameworks.

Ultrabright Fluorescent Organic Nanoparticles Based on Small-Molecule Ionic Isolation Lattices*.

Ultrabright fluorescent nanoparticles (NPs) hold great promise for demanding bioimaging applications. Recently, extremely bright molecular crystals of cationic fluorophores were obtained by hierarchical coassembly with cyanostar anion-receptor complexes. These small-molecule ionic isolation lattices (SMILES) ensure spatial and electronic isolation to prohibit aggregation quenching of dyes. We report a simple, one-step supramolecular approach to formulate SMILES materials into NPs. Rhodamine-based SMILES NPs stabilized by glycol amphiphiles show high fluorescence quantum yield (30 %) and brightness per volume (5000 M-1 cm-1 /nm3 ) with 400 dye molecules packed into 16-nm particles, corresponding to a particle absorption coefficient of 4×107  M-1 cm-1 . UV excitation of the cyanostar component leads to higher brightness (>6000 M-1 cm-1 / nm3 ) by energy transfer to rhodamine emitters. Coated NPs stain cells and are thus promising for bioimaging.

Zero-Overlap Fluorophores for Fluorescent Studies at Any Concentration.

Fluorophores are powerful tools for the study of chemistry, biology, and physics. However, fluorescence is severely impaired when concentrations climb above 5 µM as a result of effects like self-absorption and chromatic shifts in the emitted light. Herein, we report the creation of a charge-transfer (CT) fluorophore and the discovery that its emission color seen at low concentrations is unchanged even at 5 mM, some 3 orders of magnitude beyond typical limits. The fluorophore is composed of a triphenylamine-substituted cyanostar macrocycle, and it exhibits a remarkable Stokes shift of 15 000 cm-1 to generate emission at 633 nm. Crucial to the performance of this fluorophore is the observation that its emission spectrum shows near-zero overlap with the absorption band at 325 nm. We propose that reducing the spectral overlap to zero is a key to achieving full fluorescence across all concentrations. The triphenylamine donor and five cyanostilbene acceptor units of the macrocycle generate an emissive CT state. Unlike closely related donor-acceptor control compounds showing dual emission, the cyanostar framework inhibited emission from the second state to create a zero-overlap fluorophore. We demonstrated the use of emission spectroscopy for characterization of host-guest complexation at millimolar concentrations, which are typically the exclusive domain of NMR spectroscopy. The binding of the PF6- anion generates a 2:1 sandwich complex with blue-shifted emission. Distinct from twisted intramolecular charge-transfer (TICT) states, experiment-supported density functional theory shows a 67° twist inside an acceptor unit in the CT state instead of displaying a twist between the donor and acceptor; it is TICT-like. Inspired by the findings, we uncovered similar concentration-independent behavior from a control compound, strongly suggesting this behavior may be latent to other large Stokes-shift fluorophores. We discuss strategies capable of generating zero-overlap fluorophores to enable accurate fluorescence characterization of processes across all practical concentrations.