Computational study of ground-state properties of μ2 -bridged group 14 porphyrinic sandwich complexes

The structural properties of μ₂ -bridged porphyrinic double-decker complexes are investigated and the influence of various ligands, metals, substituents, and bridging atoms on the dominant structural motif is elucidated. A variety of quantum chemical methods including semiempirical (SQM) methods and density functional theory (DFT) is assessed for the calculation of ecliptic and staggered conformational energies. Local coupled cluster (DLPNO-CCSD(T1)) data are generated for reference. The r² SCAN-3c composite scheme as well as the B2PLYP-D4/def2-QZVPP approach are identified as reliable methods. Energy decomposition analyses (EDA) and localized molecular orbital analyses (LMO) are used to investigate the bonding situation and the nature of the inter-ligand interaction energy underlining the crucial role of attractive London dispersion interactions. Targeted modification of the bridging atom, e.g., by replacing O^2- by S^2- is shown to drastically change the major structural features of the investigated complexes. Further, the influence of different substituents of varying size at the phthalocyanine ligand regarding the dominant conformation is described.

Metalloporphyrins substituted with N-carbazolyl groups quadruply at meso positions

As a new family of porphyrinoids with broad absorption bands that efficiently harvest sunlight, the metal complexes of a porphyrin quadruply substituted with [Formula: see text]-carbazolyl groups at the meso positions were photometrically and structurally characterized. The porphyrins exhibited characteristic broad bands in the range of 450–500 nm, due to the charge transfer band from carbazole to porphyrin. Ligand exchange at the axial position of the zinc complex with an aquo ligand affected the absorption spectrum, and a hyper-hypsochromic shift of the broad band was observed by the coordination of methanol. Furthermore, the lowest unoccupied molecular orbital (LUMO) levels of the metalloporphyrins were lowered by the electron-withdrawing effect of the perpendicularly oriented carbazolyl groups. In the solid state, zinc-porphyrin was self-assembled into a one-dimensional coordination polymer by intermolecular axial coordination.

Dimeric Corrole Analogs of Chlorophyll Special Pairs

Chlorophyll special pairs in photosynthetic reaction centers function as both exciton acceptors and primary electron donors. Although the macrocyclic natural pigments contain Mg(II), the central metal in most synthetic analogs is Zn(II). Here we report that insertion of either Al(III) or Ga(III) into an imidazole-substituted corrole affords an exceptionally robust photoactive dimer. Notably, attractive electronic interactions between dimer subunits are relatively strong, as documented by signature changes in NMR and electronic absorption spectra, as well as by cyclic voltammetry, where two well-separated reversible redox couples were observed. EPR spectra of one-electron oxidized dimers closely mimic those of native special pairs, and strong through-space interactions between corrole subunits inferred from spectroscopic and electrochemical data are further supported by crystal structure analyses (3 Å interplanar distances, 5 Å lateral shifts, and 6 Å metal to metal distances).

Hierarchical Hybrid Metal-Organic Frameworks: Tuning the Visible/Near-Infrared Optical Properties by a Combination of Porphyrin and Its Isomer Units

Hybrid metal-organic frameworks (MOFs) with core/shell-like hierarchical structure comprised of zirconium metal and porphyrin (e.g., TPP) and its isomer, N-confused porphyrin (NCP), were synthesized through a seed-mediated reaction. The hierarchical structures of hybrid MOFs were characterized by the microscopic image analyses (e.g., scanning electron microscope (SEM), energy dispersive X-ray (EDX) spectrometry, and confocal laser scanning microscope (CLSM)). Taking advantage of the intrinsic light-harvesting properties of the porphyrin dye and the N-confused isomer, changing the core/shell layer structures of hybrid MOFs allows for tuning of the visible-to-near-infrared (NIR) absorption/emission characters, excited-state energy migrations, and photosensitization capabilities. The Förster energy transfer event occurring in the bulk MOF samples by photoexcitation enabled us to control the photoinduced singlet oxygen generation through the comprehensive light-harvesting ability of these hybrid porphyrinic MOFs. Therefore, implementation of a precisely designed porphyrin "substitute" into the MOF-based materials indeed provides a new mimic of the photosynthetic pigment system and should be potentially applicable for solar-light-driven devices.

Synthesis and characterization of β,β′-linked porphyrin-chlorin heterodimers and their metallic complexes

Two β,β′-linked porphyrin-chlorin heterodimers have been successfully synthesized with 4-fluorophenyl or 4-chlorophenyl substituted aldehyde as starting reagents. But those aldehydes with bulkier substituents did not lead to the corresponding heterodimers. These porphyrin-chlorin heterodimers and their metallic complexes have been characterized by X-ray crystallography. In all the structures, the pyrroline group in chlorin moiety and the pyrrole group in porphyrin moiety are directly connected by a single bond. Pyrroline ring has two sp[Formula: see text] hybridized carbons. The direct bonding makes the porphyrin and chlorin moieties closely contact with each other, pyrroline group and the pyrrole group forms a dihedral angle of ~70°. If porphyrin-chlorin heterodimers have bulkier substituents, the close contact could cause too much repulsion. That is probably why they can not be synthesized. For nickel complexes, the chlorin planes show large saddling and moderate ruffling conformation. The C–H⋯[Formula: see text] interaction could contribute to the saddling conformation. The distorted core makes dihedral angles and metal to metal distances between porphyrin and chlorin plane much smaller than those in their copper complexes. Their NMR, UV-visible and fluorescence spectral data have also been briefly discussed.

Electronic perturbation of supramolecular conjugates of porphyrins and phthalocyanines

The redox potential of a supramolecular porphyrin-phthalocyanine heterodimer was perturbed by the stacking of an extra metalloporphyrin to the phthalocyanine. This stacking gave rise to π-π and electrostatic interactions between the tetracationic dimer and the tetraanionic metalloporphyrin, with a Au(iii) metalloporphyrin exhibiting a larger effect than Cu(ii) and Pd(ii) complexes among square planar complexes.

Axially assembled photosynthetic reaction center mimics composed of tetrathiafulvalene, aluminum(III) porphyrin and fullerene entities

The distance dependence of sequential electron transfer has been studied in six, vertical, linear supramolecular triads, (TTF-Ph(n)-py → AlPor-Ph(m)-C60, n = 0, 1 and m = 1, 2, 3), constructed using tetrathiafulvalene (TTF), aluminum(III) porphyrin (AlPor) and fullerene (C60) entities. The C60 and TTF units are bound to the Al center on opposite faces of the porphyrin; the C60 through a covalent axial bond using a benzoate spacer, and the TTF through a coordination bond via an appended pyridine. Time-resolved optical and EPR spectroscopic methods and computational studies are used to demonstrate that excitation of the porphyrin leads to step-wise, sequential electron transfer (ET) between TTF and C60, and to study the electron transfer rates and exchange coupling between the components of the triads as a function of the bridge lengths. Femtosecond transient absorption studies show that the rates of charge separation, k(CS) are in the range of 10(9)-10(11) s(-1), depending on the length of the bridges. The lifetimes of the charge-separated state TTF˙(+)-C₆₀˙⁻ obtained from transient absorbance experiments and the singlet lifetimes of the radical pairs obtained by time-resolved EPR are in good agreement with each other and range from 60-130 ns in the triads. The time-resolved EPR data also show that population of the triplet sublevels of the charge-separated state in the presence of a magnetic field leads to much longer lifetimes of >1 μs. The data show that a modest stabilization of the charge separation lifetime occurs in the triads. The attenuation factor β = 0.36 Å(-1) obtained from the exchange coupling values between TTF˙(+) and C₆₀˙⁻ is consistent with values reported in the literature for oligophenylene bridged TTF-C60 conjugates. The singlet charge recombination lifetime shows a much weaker dependence on the distance between the donor and acceptor, suggesting that a simple superexchange model is not sufficient to describe the back reaction.

An allosteric photoredox catalyst inspired by photosynthetic machinery

Biological photosynthetic machinery allosterically regulate light harvesting via conformational and electronic changes at the antenna protein complexes as a response to specific chemical inputs. Fundamental limitations in current approaches to regulating inorganic light-harvesting mimics prevent their use in catalysis. Here we show that a light-harvesting antenna/reaction centre mimic can be regulated by utilizing a coordination framework incorporating antenna hemilabile ligands and assembled via a high-yielding, modular approach. As in nature, allosteric regulation is afforded by coupling the conformational changes to the disruptions in the electrochemical landscape of the framework upon recognition of specific coordinating analytes. The hemilabile ligands enable switching using remarkably mild and redox-inactive inputs, allowing one to regulate the photoredox catalytic activity of the photosynthetic mimic reversibly and in situ. Thus, we demonstrate that bioinspired regulatory mechanisms can be applied to inorganic light-harvesting arrays displaying switchable catalytic properties and with potential uses in solar energy conversion and photonic devices.

Photosynthetic systems regulate light harvesting via structural and electronic control of antenna proteins. Here, the authors report a light-harvesting antenna/reaction centre mimic that can be allosterically regulated using mild and redox-inactive inputs, via a coordination framework with hemilabile ligands.

Ultrafast charge separation and charge stabilization in axially linked ‘tetrathiafulvalene–aluminum(iii) porphyrin–gold(iii) porphyrin’ reaction center mimics

Sequential electron transfer leading to charge stabilization in newly synthesized vertically aligned ‘tetrathiafulvalene–aluminum(iii) porphyrin–gold(iii) porphyrin’ supramolecular triads is reported.

Porphyrins as excellent dyes for dye-sensitized solar cells: recent developments and insights

Porphyrin sensitizers have exhibited power conversion efficiencies that are comparable to or even higher than those of well-established highly efficient DSSCs based on ruthenium complexes.

Self-assembly: from amphiphiles to chromophores and beyond

Self-assembly has been recognised as a ubiquitous aspect of modern chemistry. Our understanding and applications of self-assembly are substantially based on what has been learned from biochemical systems. In this review, we describe various aspects of self-assembly commencing with an account of the soft structures that are available by assembly of surfactant amphiphiles, which are important scientific and industrial materials. Variation of molecular design using rules defined by surfactant self-assembly permits synthesis of functional nanostructures in solution and at surfaces while increasing the strength of intermolecular interactions through π-π stacking, metal cation coordination and/or hydrogen bonding leads to formation of highly complex bespoke nanostructured materials exemplified by DNA assemblies. We describe the origins of self-assembly involving aggregation of lipid amphiphiles and how this subject has been expanded to include other highly advanced chemical systems.

Synthesis and self-organization of fluorene-conjugated bisimidazolylporphyrin and its optical properties

A conjugated-bisimidazolylporphyrin bridged by bis(ethynylfluorene) was synthesized and organized into linear polymer through self-coordination having mean molecular weights, M_w and M_n, of ~2.1 × 10⁵ Da and ~1.6 × 10⁵ Da, respectively. A large two-photon absorption cross section value of 3.4 × 10⁵ GM (per dimer unit) was observed. This value was comparable to that of the previously reported self-assembled linear polymer consisting of butadiyne-bridged imidazolylporphyrins. The two-photon absorption properties could be controlled by tuning the wavelength and absorption intensity of the one-photon absorption.

Observation of proton-coupled electron transfer by transient absorption spectroscopy in a hydrogen-bonded, porphyrin donor-acceptor assembly

Proton-coupled electron transfer (PCET) kinetics of a Zn(II) porphyrin donor noncovalently bound to a naphthalene-diimide acceptor through an amidinium-carboxylate interface have been investigated by time-resolved spectroscopy. The S1 singlet excited-state of a Zn(II) 2-amidinium-5,10,15,20-tetramesitylporphyrin chloride (ZnP-beta-AmH+) donor is sufficiently energetic (2.04 eV) to reduce a carboxylate-diimide acceptor (DeltaG degrees = -460 mV, THF). Static quenching of the porphyrin fluorescence is observed and time-resolved measurements reveal more than a 3-fold reduction in the S1 lifetime of the porphyrin upon amidinium-carboxylate formation (THF, 298 K). Picosecond transient absorption spectra of the free ZnP-beta-AmH+ in THF reveal the existence of an excited-state isosbestic point between the S1 and T1 states at lambdaprobe = 650 nm, providing an effective 'zero-kinetics' background on which to observe the formation of PCET photoproducts. Distinct rise and decay kinetics are attributed to the build-up and subsequent loss of intermediates resulting from a forward and reverse PCET reaction, respectively (kPCET(fwd) = 9 x 108 s-1 and kPCET(rev) = 14 x 108 s-1). The forward rate constant is nearly 2 orders of magnitude slower than that measured for covalently linked Zn(II) porphyrin-acceptor dyads of comparable driving force and D-A distance, establishing the importance of a proximal proton network in controlling charge transport.

Porphyrin supramolecules by complementary coordination for units constructing photosynthetic systems

Among unique structural arrangements provided by nature, special pair and macroring antenna complexes in bacterial photosynthetic systems have been mimicked by simple organization of choromophores. The special pair was mimicked by imidazolyl-substituted porphyrinatozinc which gave a complementary coordination dimer of slipped cofacial orientation with an extremely large stability constant of 1010 M-1 in CHCl 3. When two imidazolylporphyrinatozinc units were linked directly at the meso positions, linear and continuous growth of the complementary coordination lead to porphyrin arrays of a few hundreds nanometer scale, corresponding to molecular weights of a few 105. At the same time, the porphyrin array could be dissociated into the monomeric unit by competitive coordination of solvents. This provided a way of terminating or initiating the oligomeric porphyrin array with appropriate chain terminals/initiators. Two imidazolylporphyrinatozinc complexes were then linked by a m-phenylene unit with an angle of 120°. The linear and macrocyclic oligomer mixtures initially obtained were converged smoothly by reorganization equilibrium into a mixture of hexameric and pentameric macrocycles under high-dilution conditions. The ring mimicked the structure and function of the light harvesting complexes of bacterial photosynthetic systems. The covalent linking of coordination organized porphyrins was also developed to maintain the structure even in highly coordinating solvents such as pyridine. The linear array formation and the facile introduction of specific terminal/initiator groups by complementary coordination were then applied to introduce antenna function onto solar cell. Through thiolate attachment on a gold surface, imidazolylporphyrinatozinc initiated the growth of meso-meso linked porphyrin arrays by successive complementary coordination. This methodology improved the efficiency of absorption of incident photon and increased significantly the total photocurrent generation efficiency.

Energy transfer in non-covalent porphyrin assemblies: through-space or through-bond?

Photosynthetic antenna arrays found in nature funnel photoexcited energy into the reaction center. Attempts have been made to mimic the antenna function by using artificial chromophores, porphyrins in particular, not only to better understand the energy-transfer processes but also to create light-harvesting devices. This review covers non-covalent porphyrin assemblies, for which intra-ensemble energy-transfer processes were characterized. The essence of the mechanisms of energy transfer is summarized and specific examples are reviewed with an emphasis put on the rate and mechanism of singlet-singlet energy transfer. As these examples demonstrate, non-covalent intra-ensemble energy-transfer processes have been ascribed to the Förster-type through-space mechanism in almost all cases. The exception is porphyrin dyad and pentad from our group based on amidinium-carboxylate salt bridges. Through-bond superexchange mechanism is proposed to account for the fast excited energy-transfer processes for these unique assemblies. The importance of intermolecular interactions not only in terms of the structural aspects but also in terms of the electronic aspects is highlighted for the design of supramolecular systems in which efficient energy transfer is desired.

Syntheses and nonlinear absorption properties of conjugated porphyrin supramolecules

Self-assemblies consisting of acetylene-linked bisporphyrins with a 4-nitrophenylethynyl substituent and with a phenylethynyl substituent were synthesized. The Q-band of the phenylethynyl-substituted compound appears at 762 nm whereas that of the 4-nitrophenylethynyl-substituted one was red-shifted to 784 nm and intensified. This may be attributed to the participation of the nitro group in the π-electronic communication system. HOMOs and LUMOs were calculated for these compounds using an INDO/S-CI method. The effective two-photon absorption cross-section values of these self-assemblies were measured by using a nanosecond open aperture Z-scan method. The maximum effective two-photon absorption cross-section values of 4-nitrophenylethynyl- and phenylethynyl-substituted bisporphyrins were obtained as 1.2 × 105 GM and 8.1 × 104 GM , respectively, at 890 nm. A 1.5 enhancement factor was obtained by introducing nitro groups, which was similar to the value previously reported for ferrocene- and fullerene-connected supramolecular porphyrin.

Syntheses and properties of acetylene-linked bis- and trisporphyrins toward two-photon photodynamic therapy

Acetylene-bridged bisporphyrins and trisporphyrins having branched bulky bis(carboxylethyl)methyl meso-substituents were synthesized. These compounds showed large effective two-photon absorption cross-section values at 890 nm measured by using a nanosecond Z-scan method. Sodium salt of hydrolyzed trisporphyrins showed broad and red-shifted Q-bands over 900 nm. Two-photon absorption cross-section values of water-soluble dimers in water were similar to, or slightly larger than, those of ester forms evaluated in toluene. Furthermore, the generation of singlet oxygen upon one-photon irradiation for dimers in water was confirmed.

Langmuir and Langmuir-Blodgett film preparation and study of a metalloporphyrin dimer molecule

Two iron complexes of a porphyrin dimer molecule were synthesized and studied at the air-water interface and in Langumir-Blodgett (LB) films. Surface pressure-area isotherm and UV-vis absorption spectroscopic studies revealed an interesting molecular switching behavior between the two iron porphyrin complexes under basic or acidic conditions. Such a reversible structural transition does not only occur in solution phase, but readily takes place in the deposited Langmuir-Blodgett films. Domains with strip or disk-like shapes were formed in the Langmuir films of the metalloporphyrin complexes when barbituric acid was added into the subphase, an indication of supramolecular network formation between the metalloporphyrin dimer and barbituric acid molecules. Magnetic property studies of the Langmuir-Blodgett films of the iron porphyrin complexes by magnetic force microscopy provide further insights into relationships between the magnetic response and molecular structures of the metalloporphyrin LB films.

Synthesis and stereochemistry of highly unsymmetric beta,meso-linked porphyrin arrays

Porphyrin arrays with tailor-made photophysical properties and well-defined three-dimensional geometries constitute attractive synthetic targets in porphyrin chemistry. The paper describes a variable, straightforward synthetic procedure for the construction of beta,meso-linked porphyrin multichromophores in good to excellent yields. In a Suzuki-type coupling reaction beta-borylated 5,10,15,20-tetraarylporphyrins (TAPs) served as versatile building blocks for the preparation of a plethora of directly linked, unsymmetrically substituted di- and triporphyrins. Besides their interesting photophysical properties, especially the trimeric porphyrin arrays show exciting stereochemical features. The established protocols thus open a convenient entry into the synthesis of achiral and chiral, unsymmetrically substituted beta,meso-linked oligoporphyrins, e.g., for applications in biomedicine or nonlinear optics.

Diastereochemically controlled porphyrin dimer formation on a DNA duplex scaffold

DNA-porphyrin conjugates were designed and synthesized for the preparation of the conformationally controlled porphyrin dimer structures constructed on a d(GCGTATACGC)2. Porphyrin derivatives were introduced to the central TATpA sequence where p represents the phosphoramidate for the attachment of the free-base porphyrin (FbP) and zinc-coordinated porphyrin (ZnP), which allows contact of the two porphyrins in the minor groove. The porphyrin dimers were characterized using CD, UV-vis, steady-state, and time-resolved fluorescence spectroscopies, indicating that the porphyrins form face-to-face conformations. Also the co-facial conformation was confirmed by comparison with spectra of the non-self-complementary duplex containing one porphyrin moiety. Introduction of zinc into porphyrin moiety destabilized the duplex formation. Two diastereomers showed different thermal stabilities and affected the conformations of porphyrin dimers. The temperature-dependent assembly and the conformational change of the porphyrin dimer on the duplex DNA were observed in the UV-vis spectra, indicating that the dynamic movement of the porphyrin dimer occurs on the duplex. The results indicate that the porphyrin dimers of DNA-FbP conjugates are overlapped clockwise and are located in the minor groove of the usual B-form DNA backbone. The interaction and conformation of two porphyrin moieties are controlled by the following three factors: (1) temperature change during and after formation of the duplex porphyrins at lower temperature; (2) diastereochemistry of the phosphoramidates where porphyrins are connected via a linker; and (3) zinc ion coordination that destabilizes the interaction of porphyrins as well duplex formation.

Synthesis and Aggregation Behavior ofmeso-Sulfinylporphyrins: Evaluation of S-Chirality Effects on the Self-Organization to S–Oxo-Tethered Cofacial Porphyrin Dimers

The synthesis and aggregation behavior of meso-sulfinylporphyrins are described. The copper-catalyzed C-S cross-coupling reaction of a meso-iodoporphyrin with benzenethiol and n-octanethiol has proved to be an efficient method for the synthesis of meso-sulfanylporphyrins, which are oxygenated by m-chloroperbenzoic acid to produce the corresponding meso-sulfinylporphyrins. Optically active zinc meso-sulfinylporphyrins were successfully isolated by means of optical resolution of the racemates on a chiral HPLC column. Zinc sulfinylporphyrins readily undergo self-organization through S-oxo-zinc coordination to form cofacial porphyrin dimers in solution, in which the hetero- and homodimers are present as a diastereomeric mixture. The aggregation modes of the S-oxo-tethered porphyrin dimers were fully characterized by 1H NMR, IR, and UV/Vis spectroscopy as well as DFT calculations on their model compounds, thus revealing that the self-aggregation behavior depends on the combination of S chirality. The absolute configurations at the sulfur center can be determined by the exciton-coupled CD method. The observed self-association constant for the S-oxo-tethered dimerization of (S)-phenylsulfinylporphyrin in toluene is larger than that in dichloromethane, which reflects the difference in dipole moments between the homodimer and the monomer. In cyclic and differential pulse voltammetry, the first oxidation process of the cofacial dimers is split into two reversible steps, which indicates that the initially produced pi radical cations are delocalized efficiently between the two porphyrin rings. The present findings demonstrate the potential utility of meso-sulfinyl groups as promising ligands for investigating the effects of peripheral chirality on the structures and optical and electrochemical properties of metal-assisted porphyrin self-assemblies.

Porphyrin Light-Harvesting Arrays Constructed in the Recombinant Tobacco Mosaic Virus Scaffold

We have demonstrated the construction of multiple porphyrin arrays in the tobacco mosaic virus (TMV) supramolecular structures by self-assembly of recombinant TMV coat protein (TMVCP) monomers, in which Zn-coordinated porphyrin (ZnP) and free-base porphyrin (FbP) were site-selectively incorporated. The photophysical properties of porphyrin moieties incorporated in the TMV assemblies were also characterized. TMV-porphyrin conjugates employed as building blocks self-assembled into unique disk and rod structures under the proper conditions as similar to native TMV assemblies. The mixture of a ZnP donor and an FbP acceptor was packed in the TMV assembly and showed energy transfer and light-harvesting activity. The detailed photophysical properties of the arrayed porphyrins in the TMV assemblies were examined by time-resolved fluorescence spectroscopy, and the energy transfer rates were determined to be 3.1-6.4x10(9) s(-1). The results indicate that the porphyrins are placed at the expected positions in the TMV assemblies.

Selective Inclusion of Electron-Donating Molecules into Porphyrin Nanochannels Derived from the Self-Assembly of Saddle-Distorted, Protonated Porphyrins and Photoinduced Electron Transfer from Guest Molecules to Porphyrin Dications

A doubly protonated hydrochloride salt of a saddle-distorted dodecaphenylporphyrin (H2DPP), [H4DPPP]Cl2, forms a porphyrin nanochannel (PNC). X-ray crystallography was used to determine the structure of the molecule, which revealed the inclusion of guest molecules within the PNC. Electron-donating molecules, such as p-hydroquinone and p-xylene, were selectively included within the PNC in sharp contrast to electron acceptors, such as the corresponding quinones, which were not encapsulated. This result indicates that the PNC can recognize the electronic character and steric hindrance of the guest molecules during the course of inclusion. ESR measurements (photoirradiation at lambda>340 nm at room temperature) of the PNC that contains p-hydroquinone, catechol, and tetrafluorohydroquinone guest molecules gave well-resolved signals, which were assigned to cation radicals formed without deprotonation based on results from computer simulations of the ESR spectra and density functional theory (DFT) calculations. The radicals are derived from photoinduced electron transfer from the guest molecules to the singlet state of H4DPP2+. Transient absorption spectroscopy by femtosecond laser flash photolysis allowed us to observe the formation of 1(H4DPP2+)*, which is converted to H4DPP+. by electron transfer from the guest molecules to 1(H4DPP2+)*, followed by fast disproportionation of H4DPP+., and charge recombination to give diamagnetic species and the triplet excited state 3(H4DPP2+)*, respectively.

Modular approach toward supramolecular functional assemblies: characterization of Donor-spacer-acceptor ternary complexes

It is shown that the noncovalent donor-spacer-acceptor (DSA) motif is useful in constructing an electron-transfer assembly. As a representative example, the equilibrium and structure of one of the DSA assemblies, consisting of Zn-tetraphenylporphyrin, a spacer unit bearing pyridine and amidinium moieties, and 3,4-dinitrobenzoic acid, were studied in detail by the extensive use of UV-vis titration, fluorescence spectroscopy, and 1H NMR, with the help of a three-component equilibrium model. Complex formation and fluorescence quenching in 20 different DSA complexes constructed from a library of five donors, two spacers, and two acceptors were investigated. It has been experimentally shown that supramolecular modular approach is useful for a systematic and quick search for a functionally optimized assembly.