Donor-acceptor Systems Research Articles

Biological and computational exploration of a hydrogen-bonded charge transfer complex between 8-Hydroxyquinoline and Benzene-1,4-diol in different polar solvents: Synthesis and spectrophotometric analysis

The formation and characterization of a charge transfer complex (CTC) between 8-Hydroxyquinoline and Benzene-1,4-diol (Quinol) in various polar solvents. CTCs, marked by weak yet significant interactions, are pivotal in understanding electron transfer processes and molecular recognition phenomena. The choice of 8-Hydroxyquinoline (8HQ) as the donor and Quinol (Q) as the acceptor facilitates the investigation of their interaction, given their respective electron-rich and electron-poor properties. The spectroscopic analysis, including Fourier-transform infrared (FTIR) and UV-visible spectroscopy, reveals shifts in molecular vibrations and electronic transitions, indicating the formation of the CTC. Additionally, thermal analysis techniques, such as thermogravimetric analysis (TGA) and differential thermal analysis (DTA), provide insights into the thermal stability and decomposition behavior of the CTC. Powder X-ray diffraction (PXRD) analysis offers data on the crystalline structure and morphology of the complex. Furthermore, the manuscript explores the biological significance of the synthesized CTC, including its antioxidant, antibacterial, and antifungal activities. Conductivity measurements and computational studies, such as Density Functional Theory (DFT) and molecular docking, provide further insights into the electronic properties and structural characteristics of the CTC. Overall, the study contributes to advancing the understanding of CTCs and their applications, particularly in the context of novel donor-acceptor systems. The insights gained have implications in diverse fields, including materials science, biomedical engineering, and fundamental chemistry, paving the way for tailored molecular design and functional applications.

Charge Transfer and Intersystem Crossing in Compact Naphthalenediimide-Phenothiazine Triads: Synthesis and Study of the Photophysical Property with Transient Optical and Electron Paramagnetic Resonance Spectroscopic Methods.

In order to obtain a long-lived charge separation (CS) state in compact electron donor-acceptor molecular systems, we prepared a series of naphthalenediimide (NDI)-phenothiazine (PTZ) triads, with phenylene as the linker between the donor and acceptor. Conformation restriction is imposed to control the mutual orientation of the NDI and PTZ units by attaching methyl groups on the phenylene linker to tune the electronic coupling between the donor and the acceptor. Moreover, the PTZ moiety was oxidized to sulfoxide to tune the ordering of the CS state and the 3LE state (LE: locally excited state). UV-vis absorption spectra indicate electronic coupling between NDI with the phenylene linker as well as the PTZ units, manifested by the appearance of a charge-transfer (CT) absorption band, whereas this coupling is devoid in the triads with conformation restriction imposed. Fluorescence is strongly quenched in the triads compared to the reference compound, indicating electron transfer upon photoexcitation. Femtosecond transient absorption spectra indicate that the CS takes 0.8 ps, and then the 3LE state is formed by charge recombination in 83 ps. Nanosecond transient absorption (ns-TA) spectra show that the 3NDI state was observed in nonpolar solvents such as cyclohexane (triplet state lifetime: 95.7 μs), whereas the CS state was observed in more polar solvents. The CS state lifetimes are up to 1.2 μs (in toluene). Time-resolved electron paramagnetic resonance spectra of the triads in toluene consist of two types of signals: CS states (narrower signals, ∼10 mT) and 3LE states (broader signals, ∼50 to 200 mT). In the spectra of the triads containing PTZ, the CS state signals dominate, whereas for the triads containing oxidized PTZ, the 3NDI signals (zero-field splitting D ≈ 2000 MHz) prevail, both observations being in agreement with the ns-TA spectral studies. The electron spin polarization phase pattern of the 3NDI states of the triads indicates that the intersystem crossing (ISC) mechanism is spin-orbit charge-transfer ISC. Considering the 3CS state as ion pairs, the electron-exchange energy (J) is determined to be -39 to -59 MHz, and the electron spin dipolar interaction is 83-92 MHz.

An investigation of the Excitation Wavelength-Dependent Dynamic Changes in the Mechanism of Detection of Picric Acid using Pyrene-Based Donor-Acceptor Systems.

Picric acid (PA) is an important industrial feedstock and hence the release of industrial effluents without proper remediation results in its buildup in soil and water bodies. The adverse effects of PA accumulation in living beings necessitate the development of efficient methods for its detection and quantification. Herein, we describe pyrene-based fluorescent sensors for PA, where pyrene is appended with electron-withdrawing groups, malononitrile, and 2-(3-cyano-4,5,5-trimethylfuran-2(5H)-ylidene) malononitrile (DCDHF). These molecules displayed the typical emission of pyrene monomers, as well as a broad red-shifted emission resulting from an intramolecular charge transfer (ICT) in the excited state. Both the emissions displayed a turn-off response to PA with high selectivity and sensitivity and the lowest limit of detection was estimated as 27 nM. To prove the feasibility of on-site detection, test paper strips were prepared, which could detect PA up to 4.58 picograms. Using a combination of experimental and theoretical studies the mechanism of the detection was identified as primary/secondary inner filter effect, oxidative photoinduced electron transfer, or a combination of both depending on the excitation wavelength. Interestingly, the contribution of each of these mechanisms to the total quenching process varied with a change in the excitation wavelength.

Novel Benzothiadiazole-based Donor-Acceptor Systems: Synthesis, Ultrafast Charge Transfer and Separation Dynamics.

Near-infrared (NIR) absorbing electron donor-acceptor (D-A) chromophores have been at the forefront of current energy research owing to their facile charge transfer (CT) characteristics, which are primitive for photovoltaic applications. Herein, we have designed and developed a new set of benzothiadiazole (BTD)-based tetracyanobutadiene (TCBD)/dicyanoquinodimethane (DCNQ)-embedded multimodular D-A systems (BTD1-BTD6) and investigated their inherent photo-electro-chemical responses for the first time having identical and mixed terminal donors of variable donicity. Apart from poor luminescence, the appearance of broad low-lying optical transitions extendable even in the NIR region (>1000 nm), particularly in the presence of the auxiliary acceptors, are indicative of underlying nonradiative excited state processes leading to robust intramolecular CT and subsequent charge separation (CS) processes in these D-A constructs. While electrochemical studies identify the moieties involved in these photo-events, orbital delocalization and consequent evidence for the low-energy CT transitions have been achieved from theoretical calculations. Finally, the spectral and temporal responses of different photoproducts are obtained from femtosecond transient absorption studies, which, coupled with spectroelectrochemical data, identify broad NIR signals as CS states of the compounds. All the systems are found to be susceptible to ultrafast (~ps) CT and CS before carrier recombination to the ground state, which is, however, significantly facilitated after incorporation of the secondary TCBD/DCNQ acceptors, leading to faster and thus efficient CT processes, particularly in polar solvents. These findings, including facile CT/CS and broad and intense panchromatic absorption over a wide window of the electromagnetic spectrum, are likely to expand the horizons of BTD-based multimodular CT systems to revolutionize the realm of solar energy conversion and associated photonic applications.

A Strained Donor-Acceptor Carbon Nanohoop: Synthesis, Photophysical and Charge Transport Properties.

Herein, we report the synthesis of a novel intramolecular donor-acceptor (D-A) system ([12]CPP-8TPAOMe) based on cycloparaphenylenes (CPPs) grafted with eight di(4-methoxyphenyl)amino groups (TPAOMe) as donors. Compared to [12]CPP, D-A nanohoop exhibited significant changes in physical properties, including a large redshift (>78 nm) in the fluorescence spectrum and novel positive solvatofluorochromic properties with a maximum peak ranging from 484 nm to 546 nm. The potential applications of [12]CPP-8TPAOMe in electron- and hole-transport devices were further investigated, and its bipolar behavior as a charge transport active layer was clearly observed.

Crystal structure and stimulus-responsive properties of three functional compounds containing 1-carboxyethyl-4,4′-bipyridine

Herein, three compounds containing the neutral viologen derivative, 1-carboxyethyl-4,4′-bipyridine (CEbpy) have been synthesized, (CEbpy)·(H2TPDC)·2H2O (1) [Co(CEbpy)(TPDC)(H2O)4]·3H2O (2) and [Cd3(CEbpy)2(TPDC)3·7H2O]n (3) (H2TPDC = thiophene-2,5-dicarboxylic acid). Compound 1 is a supramolecular assembly, linked by non-covalent interactions to constitute the donor-acceptor (D-A) system. Compound 2 owns a zero-dimensional (0D) isolated structure in which metal ions are coordinated with CEbpy and fully deprotonated (TPDC)2- ligands. Compound 3 exhibits a three-dimensional (3D) framework of trinuclear metal clusters, where each metal atom forms its own distinct linear one-dimensional (1D) chain along a specific axis. Although the three compounds comprise the same bipyridinium moiety and aromatic acid, their chromic behaviors are different. Compounds 1 and 3 exhibit reversible photochromism, while 2 reveals hydrochromism upon heating. Additionally, photo-modulated fluorescence as well as their potential applications in inkless erasable printing have been studied.

Synthesis, Spectral and Electrochemical Properties, and Theoretical Studies of Highly Functionalized Fused Triazole-Isoindoline Derivatives as a Donor-Acceptor System

Triazole and propargyl group functionalities are frequently utilized in the construction of efficient blue-emitting materials, serving as acceptors and donors, respectively. Leveraging the synergistic effect of donor-acceptor coupling between these moieties, three new compounds, namely CB-But-I2, Ph-But-I2, and DP-But-I2, were synthesized. Given the advantageous strategy of combining electron donors and acceptors to optimize carrier injection and transport, CB-But-I2, Ph-But-I2, and DP-But-I2 demonstrate remarkable capabilities in both hole and electron transportation. A metal-free synthesis approach was employed to produce highly functionalized 1,2,3-triazole cores incorporating electronic donor and acceptor functionalities. This synthesis method involved the “Click reaction” ring formation between acetylene and azide compounds of 2-(4-bromobutyl) isoindoline-1,3-dione, catalyzed by copper sulfate pentahydrate and assisted by ascorbic acid as a base. The process boasts several advantages, including mild reaction conditions, accessibility of precursors, metal-free synthesis, straightforward setup, and the generation of various substituted regioselective triazole compounds in satisfactory yields. All synthesized compounds were found to possess thermal stability and exhibited fluorescence within the 292–355 nm range. Moreover, a significant positive solvato-chromic behavior was noted across different solvents with varying polarities, and the theoretical values were compared against experimental data for validation.

Theoretical Study of the Exciplex Formation in an m-MTDATA–BPHEN OLED

The formation of charge-transfer (CT) exciplexes in m-MTDATA–BPhen (4,4',4''-tris[(3-methylphenyl)phenylamino]-triphenylamine)–bathophenanthroline) donor-acceptor pair is studied using density functional theory (DFT) and multireference quantum chemistry. It is shown that the lowest excited singlet S1 and one of the low-lying triplets have the CT character, while the lowest triplet is localized on the BPhen molecule, which agrees with the experimental fluorescence and phosphorescence data. A multireference treatment agrees with the DFT calculations and shows that the CT character of the exciplex states in such donor-acceptor systems is not an artifact of the functional.

New conjugated copolymer MEH-PPV-P3HT with donor-acceptor system for organic optoelectronics applications: Experimental and theoretical study

Donor-acceptor architecture was designed of new diblocks copolymer MEH-PPV-P3HT synthesis. The new copolymer was elaborated through oxidative pathway. The correlation structure-properties and their potential photophysical characteristics of the obtained material were reported utilizing several characterization analyses (InfraRed, Raman, TGA, UV visible spectroscopy, as well as PL and TRPL). To define the model's geometric structure, vibrational, and optoelectronic properties of the studied copolymer, Density Functional Theory DFT and Time-dependent Density Functional Theory TD-DFT approach were carried out. The obtained copolymer exhibits great thermal stability and substantial absorption in the visible range. An energy gap lower than the original materials by the amount of 1.74 eV which proves the presence of the charge transfer process. In addition, due to Forster energy transfer from the MEH-PPV to the P3HT an enhancement of the exciton average lifetime was detected. The obtained results from the copolymer characterization suggest a potential for application in organic optoelectronic devices. A good accordance between experimental and theoretical results based DFT calculations is obtained.

Non-covalent self-assembly of substituted phthalocyanine with C60, C70, and 9-phenylanthracene: Spectroscopic insights and DFT calculations

Self-assembly of non-covalent donor-acceptor systems based on (octakis-3,5-di-tert-butylphenoxy)phthalocyanine (H2Pc(3,5-tBuPhO)8) and С60, С70 or 9-phenylanthracene (PhAn) is observed and described using the UV–vis and steady-state/time-resolved fluorescence methods. The 1:1 stoichiometry of the H2Pc(3,5-tBuPhO)8 - С60/С70/PhAn supramolecule was established by Job's method. The fluorescence quenching of phthalocyanine in the mentioned systems in toluene, indicating close bonding between a donor and an acceptor, was observed. The bonding constants are 1.2 × 104 M−1, 2.4 × 104 M−1, and 3.9 × 102 M−1 for the C60, C70, and PhAn derivatives, respectively. Using time-resolved fluorescence measurements, the static mechanism of quenching was established. The H2Pc(3,5-tBuPhO)8 fluorescence lifetimes in the absence and presence of С60/С70/PhAn, the charge separation rate constant (kCS) and the charge-separated state quantum yield (ΦCS) of donor-acceptor systems were calculated. (С70)H2Pc(3,5-tBuPhO)8 displays the highest kCS and ΦCS in good agreement with its stability parameter. Quantum-chemical calculations of the molecular spatial/electronic structure and the HOMO/LUMO composition that were revealed by DFT and TD DFT methods point to the H2Pc(3,5-tBuPhO)8 → fullerenes redistribution of the electron density and to the opposite one in the PhAn complex.

Engineering delocalized π-electron and donor-acceptor system in polymeric carbon nitride for efficient photocatalytic hydrogen evolution

A facile “one-pot” method was adopted to engineer delocalized π-electron and Donor-Acceptor (D-A) system in polymeric carbon nitride (PCN). The resulting UCN-xTAB materials demonstrate an expanded light absorption range due to the expanded delocalization with the graft of 1,3,5-benzenetriamine (TAB) into the CN network. The constructed D-A system further promote the exciton dissociation and charge migration. Consequently, the optimized samples UCN-5TAB displays a remarkable apparent quantum efficiency (AQE) (20.2 %) for H2 production at 450 nm, surpassing the performance of previously reported PCN-based photocatalysts. The proposed structure for UCN-xTAB was confirmed by Density-functional-theory (DFT) calculations. In addition, the regulation of delocalization can be probed by tuning the incorporated monomers (melamine, 2,4,6-triaminopyrimidine), demonstrating the significance of delocalization for enhanced photocatalytic activity. This work provides a deep understanding on the role delocalization and D-A structure of PCN for efficient photocatalytic activity with improved solar harvesting in long wavelength region.

Axial Coordinated Manganese(III) Porphyrin/Tetraazaporphyrin - 4-(10-phenylanthracen-9-yl)Pyridine Dyads: Self-Assembly, Structure and Spectral Properties in Ground and Excited States.

Self-assembly of new donor-acceptor systems based on (5,10,15,20-tetraphenylporphinato)manganese(III)/(5,10,15,20-tetra-4-tert-butylphenylporphinato)manganese(III)/(octakis(4-tert-butylphenyl)tetraazaporphinato)manganese(III) acetate ((AcO)MnTPP/(AcO)MnTBPP/(AcO)MnTAP) and 4-(10-phenylanthracen-9-yl)pyridine (PyAn) was studied using fluorescence spectroscopy and mass spectrometry. It was found that the coordination complexes of 1 : 1 composition (dyads) are formed in toluene. The spectral properties, the chemical structures and redox behavior of the dyads were described using 1H NMR, IR, ESR spectroscopy and cyclic voltammetry, respectively. The dynamic processes and the characteristics in the excited state of the dyads were obtained using the femtosecond transient absorption spectroscopy method. Density functional theory (DFT), time-dependent DFT methods were used to elucidate the dyad electronic structures and to establish the differences in their frontier molecular orbitals. The analysis of the lambda parameter and the distance of hole-pair interaction was indicated more favorable charge transfer between the macrocycle and the axial PyAn fragment in (AcO)(PyAn)MnTAP. The calculated values of the zero-field splitting parameters D and E/D, together with the g tensors of the lowest spin-orbit state for (AcO)MnTPP and (AcO)(PyAn)MnTPP were obtained using the combination of DFT and Multireference Perturbation Theory (CASSCF/NEVPT2) simulations. The data obtained develop the fundamental basis in the field of photovoltaics and show the prospects for the study of molecular systems of this class.

On population-space description of chemical reactivity

The electron-population degrees-of-freedom of donor-acceptor systems are reexamined and alternative simple models of charge-transfer reactivity are discussed in the substrate and atomic resolutions. The in situ differential descriptors of the polarized subsystems are emphasized and alternative energy profiles in interactions between hard and soft acidic and basic reactants are used to investigate the process representative activation and reaction energies. The intersecting-state model of such acid-base (AB) systems is explored, its predictions of the reaction transition-state complex and its properties are summarized, and composite (AB)n systems are commented upon.

Magic Angle Spinning Solid-State 13C Photochemically Induced Dynamic Nuclear Polarization by a Synthetic Donor-Chromophore-Acceptor System at 9.4 T.

Solid-state photochemically induced dynamic nuclear polarization (photo-CIDNP) is a nuclear magnetic resonance spectroscopy technique in which nuclear spin hyperpolarization is generated upon optical irradiation of an appropriate donor-acceptor system. Until now, solid-state photo-CIDNP at high magnetic fields has been observed only in photosynthetic reaction centers and flavoproteins. In the present work, we show that the effect is not limited to such biomolecular samples, and solid-state 13C photo-CIDNP can be observed at 9.4 T under magic angle spinning using a frozen solution of a synthetic molecular system dissolved in an organic solvent. Signal enhancements for the source molecule larger than a factor of 2300 are obtained. In addition, we show that bulk 13C hyperpolarization of the solvent can be generated via spontaneous 13C-13C spin diffusion at natural abundance.

Intramolecular Charge Transfer and Stimuli-Responsive Emission in Cholesterol-Appended Phenothiazine-Cyanostyryl-Based Donor-Acceptor Systems.

Organic fluorescent molecules have received considerable attention owing to their various optoelectronic applications. Herein, we report the design and synthesis of two cholesterol-functionalized cyanostyrene-phenothiazine-based D-π-A systems that are emissive in both the solution and solid states. The newly synthesized cholesterol-appended phenothiazine-cyanostyrene diads PTCS-1 and PTCS-2 vary in the N-alkylation of phenothiazine, respectively, with─octyl and─hexyl chains. Both molecules are highly fluorescent and show reasonably good quantum yields in nonpolar solvents because of twisted intramolecular charge transfer (TICT). The molecules exhibit aggregation-induced emission in the solid state. Due to the presence of flexible alkyl chains in the phenothiazine and cholesterol moieties, PTCS-1 and PTCS-2 show mechanochromic luminescence switching in response to external shear stress and emission recovery under methanol vapor. Powder X-ray diffraction studies prove that the emission switching on the applied stimuli in both PTCS-1 and PTCS-2 is attributed to the reversible transformation between the crystalline and amorphous states. Time-dependent density functional theory (TD-DFT) studies are carried out to gain insight into the ICT interactions. TD-DFT analysis at the TD-M06-2X/def2-TZVP level further revealed that in both molecules, the lowest unoccupied molecular orbital (LUMO) + 2, LUMO, highest occupied molecular orbital (HOMO), and HOMO - 1 orbitals are responsible for the charge transfer interactions. These ICT interactions are identified as π-π* type interactions.

Defect‐Rich Graphdiyne Quantum Dots as Efficient Electron‐Donors for Hydrogen Generation

AbstractDownsizing the graphdiyne (GDY) network to shape quantum dots (QDs) will provide attractive optical and electronic properties associated with quantum confinement and edge effects. Here, it is demonstrated that quantum confinement and defect introduction allow using GDY in donor–acceptor photocatalytic systems for solar‐to‐hydrogen conversion. The defect‐rich GDY QDs (GDYO‐QDs) exhibit a blue‐to‐green excitation‐dependent photoluminescence behavior, demonstrating their ability to harvest light over a wide energy range. Quantum‐chemical calculations evidenced an increase in the electronic bandgap of GDY upon quantum confinement and defect introduction without the appearance of trap states that can hamper charge transport properties. Such a unique optical behavior of QDs is used in photocatalytic hydrogen generation through the hybridization with TiO2 as a model photocatalyst. Theoretical and experimental results demonstrate that the donor−acceptor system tremendously boosts the photocatalytic performance, reaching 5288 µmol g−1 after 4 h of illumination at a constant rate of 1322 µmol g−1 h−1, using a low volume of a sacrificial electron donor (6% v/v). The QDs act as efficient chromophores harvesting UV and visible light while injecting electrons into the TiO2. This work opens a new area of using GDYO‐QDs as an efficient chromophore in developing donor–acceptor systems for photocatalysis and future photovoltaic devices.

Synthesis, Characterization, and Properties of a Titanium(IV)-Tetrathiafulvalene-Based Complex.

To deeply investigate the interaction between a tetrathiafulvalene (TTF) unit and a Ti(IV) center, a monomeric heteroleptic octahedral Ti(IV) complex containing a diimine ligand composed of a 1,10-phenanthroline core fused with a TTF fragment (ligand 2a) was prepared. The stable complex formulated as Ti(1)2(2a), where 1 is a 2,2'-biphenolato derivative, was efficiently synthesized by following a one-step approach. This complex and its model species [Ti(1)2(2b)] were fully characterized in solution, and their solid-state structures were established by single-crystal X-ray diffraction analysis. Density functional theory calculations allowed the assignment of the frontier orbitals involved in the electronic transitions characterized by ultraviolet-visible absorption spectroscopy. Electrochemical and spectroelectrochemical studies revealed that the TTF unit within Ti(1)2(2a) can undergo two reversible one-electron oxidation processes; a reversible one-electron reduction of the Ti(IV) atom was highlighted. The photophysical measurements performed for this donor-acceptor molecular system indicated that an electron transfer process upon light excitation occurred within Ti(1)2(2a).

Piperazine appended naphthalimide-based organic scaffolds exhibiting efficient aggregation induced emission (AIE) and selective picric acid sensing

AIEgens (5a−5c &6a−6c) derived from piperazine-appended naphthalimide have been synthesized via strategic modifications following multi-step process. Resulting compounds have been thoroughly characterized by spectroscopic techniques (IR, NMR (1H &13C), HRMS, UV/Vis and fluorescence spectroscopy). The compounds under study represent an asymmetric donor-acceptor (D-A) system with a D-A′-π-A construct. Expectedly, these display efficient aggregation-induced emission (AIE) which has been followed by UV/Vis, fluorescence, fluorescence lifetime and morphological (SEM) studies. Morphological studies on these systems revealed spherical nanostructures in aggregated state. These compounds display solid-state emission and solvatochromism. It has been observed that the donor unit plays a crucial role in directing photophysical properties including AIE. Moreover, synthesized compounds exhibited selective sensing toward picric acid. Further, DFT studies have been performed to support and co-relate the physical properties.

Unraveling the Molecular Weight Dependence of High Magnetic Field to Manipulate the Semiconducting Polymer Molecular Orientation.

The magnetic alignment of molecules, which exploits the anisotropy of diamagnetic susceptibility, provides a clean and versatile approach to the structural manipulation of semiconducting polymers. Here, the magnetic-alignment dynamics of two molecular-weight (MW) batches of a diketopyrrolopyrrole (DPP)-based copolymer (PDVT-8) were investigated. Microstructural characterizations revealed that the magnetically aligned, high-MW (Mn = 53.7 kDa) PDVT-8 film exhibited a higher degree of backbone chain alignment and film crystallinity compared with the low-MW (Mn = 17.6 kDa) PDVT-8 film grown via the same magnetic alignment method. We found that as the MW increases, the degree of preaggregation of the polymer molecules in solution significantly increases and the aggregation mode changes from H-aggregation to J-aggregation through a cooperative assembly mechanism. These events improved the responsiveness of high-MW polymer molecules to magnetic fields. Field-effect transistors based on the magnetic aligned high-MW PDVT-8 films exhibited a 6.8-fold increase in hole mobility compared to the spin-coated films, along with a mobility anisotropy ratio of 12.6. This work establishes a significant correlation among chain aggregation behavior in solution, polymer film microstructures, magnetic responsiveness, and carrier transport performance in donor-acceptor polymer systems.

Silylium-Catalyzed Activation of Donor- Acceptor Strained Rings and Annulation with Indoles.

Leveraging the unique reactivity profile of donor-acceptor aminocyclopropanes and cyclobutanes allows the preparation of complex nitrogen-substituted molecules. While most reports focus on donor-acceptor strained rings with two geminal carbonyl groups as acceptors, mono carbonyl acceptor systems, despite their synthetic relevance, have been considerably less studied. Herein we describe catalytic annulation reactions ofaminocyclopropane and aminocyclobutane monoesters employing silylium catalysis to activate these less reactive donor-acceptor systems.