In light of the considerable impact synthetic 2D polymers are expected to have on many fundamental and applied aspects of the natural and engineering sciences, it is surprising that little research has been carried out on these intriguing macromolecules. Although numerous approaches have been reported over the last several decades, the synthesis of a one monomer unit thick, covalently bonded molecular sheet with a long-range ordered (periodic) internal structure has yet to be achieved. This Review provides an overview of these approaches and an analysis of how to synthesize 2D polymers. This analysis compares polymerizations in (initially) a homogeneous phase with those at interfaces and considers structural aspects of monomers as well as possibly preferred connection modes. It also addresses issues such as shrinkage as well as domain and crack formation, and briefly touches upon how the chances for a successful structural analysis of the final product can possibly be increased.

Two‐Dimensional Polymers: Just a Dream of Synthetic Chemists?

The self-assembly and self-organization of porphyrins and related macrocycles enables the bottom-up fabrication of photonic materials for fundamental studies of the photophysics of these materials and for diverse applications. This rapidly developing field encompasses a broad range of disciplines including molecular design and synthesis, materials formation and characterization, and the design and evaluation of devices. Since the self-assembly of porphyrins by electrostatic interactions in the late 1980s to the present, there has been an ever increasing degree of sophistication in the design of porphyrins that self-assemble into discrete arrays or self-organize into polymeric systems. These strategies exploit ionic interactions, hydrogen bonding, coordination chemistry, and dispersion forces to form supramolecular systems with varying degrees of hierarchical order. This review concentrates on the methods to form supramolecular porphyrinic systems by intermolecular interactions other than coordination chemistry, the characterization and properties of these photonic materials, and the prospects for using these in devices. The review is heuristically organized by the predominant intermolecular interactions used and emphasizes how the organization affects properties and potential performance in devices.

Self-Organized Porphyrinic Materials

Supramolecular chemistry, defined as “chemistry outside a molecule”, is at the heart of the development of chemistry of complex systems, molecular devices, ensembles, and nanochemistry.1 This is the chemistry where molecules are able to self-organize, self-assemble, and self-control into systems and the components are often analogues to biological molecules. Metalloporphyrins and metallophthalocyanines are remarkable precursors in supramolecular chemistry, and the rapid development of this chemistry led to assemblies possessing various architectures and properties (photo-, electro-, and catalytic properties and others). Metalloporphyrins are one of the cornerstones on which the existence of life is based, and major biochemical, enzymatic, and photochemical functions depend on the special properties of a tetrapyrrolic macrocycle. However, metalloporphyrins are the only molecules as key elements that require assembly with other elements to form the supramolecular structure, that is, the working device. In natural systems, polypeptides define a given structural organization and hold all the moieties together. Such complex natural devices are not accessible by direct chemical synthesis so far, but their modeling, using simplified designs, has been actively exploited during the last decades. The rapid development of this new area of chemistry has promoted the understanding of the concepts of design and strategies of self-assembly of structures based on intermolecular interactions to result in natural and synthetic supramolecular complexes of metalloporphyrins. Synthetic metalloporphyrin complexes are often used as analogues of natural systems found in photosynthesis, oxygen carriers, and catalysts.2,3 Such research also led to the discovery of new applications of these systems, for example in photodynamic therapy, information storage devices or photoelectrical devices that transform energy in both directions (photocells and lightemitting diodes).4-6 An application of increasing importance is the use of metalloporphyrins as receptors, exploiting their ability to selectively form complexes which can sharply change the spectral properties.7,8 Using molecules that combine different receptor units such as porphyrins and † A.N. Frumkin Institute of Physical Chemistry and Electrochemistry. ‡ Université de Bourgogne. Irina Beletskaya was born in 1933 in Leningrad (USSR). She received her Diploma in 1955, her Ph.D. in 1958, and her Doctor of Chemistry degree in 1963, all at M.V. Lomonosov Moscow State University. The subject for the latter was “Electrophilic Substitution at Saturated Carbon”. She became a Full Professor in 1970. She is currently a head of the Laboratory of Organoelement Compounds at M.V. Lomonosov Moscow State University and a full member (Academician) of Russian Academy of Sciences. She was a recipient of the Lomonosov Prize (1979), the Mendeleev Prize (1982), and the Nesmeyanov Prize (1991). Irina Beletskaya is a chief editor of the Russian Journal of Organic Chemistry. She is the author of more than 1000 articles and a number of monographs. Her current scientific interests are focused on organoelement compounds, transition metal catalysis, and organocatalysis. Chem. Rev. 2009, 109, 1659–1713 1659

Supramolecular chemistry of metalloporphyrins.

Porphyrins as Molecular Electronic Components of Functional Devices

7.1. Synthesis 306 7.2. Spectroscopic and Redox Properties 307 7.2.1. Optical Spectroscopy 307 7.2.2. Redox Properties 310 7.2.3. Other Characterization Methods 312 8. seco-Porphyrazines 312 8.1. Synthesis 312 8.2. Spectroscopic and Redox Properties 312 8.2.1. Optical Spectroscopy 312 8.2.2. Redox Properties 313 8.2.3. Other Characterization Methods 313 9. Conclusions 313 10. Abbreviations 314 11. Acknowledgments 314 12. References 314

Low Symmetry Phthalocyanines and Their Analogues

Die Kinetik der entarteten Cope-Umlagerungen der Titelverbindungen wurden mittels dynamischer 13C-NMR-Spectroskopie gemessen. Die aus den NMR-Linienformanderungen abgeleiteten Reaktionsgeschwindigkeitskonstanten k lieferten auf der Basis der Eyring-Gleichung folgende Aktivierungsparameter: Semibullvalen (1) ΔH≠ = 5.2 kcal mol−1, ΔS≠ = –3.2 cal K−1 mol−1, ΔG≠298 = 6.2 kcal mol−1; 1,5-Dimethylsemibullvalen (2) ΔH≠ = 4.5 kcal mol−1, ΔS≠ = –1.6 cal K−1 mol−1, ΔG≠298 = 5.0 kcal mol−1; 2,6-Dibrom-1,5-dimethylsemibullvalen (3) ΔH≠ = 7.5 kcal mol−1, ΔS≠ ≈ 0 cal K−1 mol−1, ΔG≠298 = 7.4 kcal mol−1. Die Substituenteneffekte werden mit denen anderer substituierter Semibullvalene verglichen und im Hinblick auf die Natur des Ubergangszustandes der Cope-Umlagerung in uberbruckten Homotropilidenen diskutiert. Die fur 2 bestimmte Barriere ist die niedrigste, die bisher mit der dynamischen NMR-Spektroskopie gemessen wurden.



Applications of 13C-NMR Spectroscopy, XXVII. – Activation Parameters off the Cope Rearrangements of semibullvalene, 1,5-Dimethylsemibullvalene, and 2,6-Dibromo-1,5dimethylsemibullvalene



The kinetics of the degenerate Cope rearrangements of the title compounds were measured by dynamic 13C-NMR spectroscopy. The rate constants derived from the changes in NMR lineshape yielded, on the basis of the Eyring equation, the following activation parameters: semibullvalene (1) ΔH≠ = 5.2 kcal mol−1, ΔS≠ = –3.2 cal K−1 mol−1, ΔG≠298 = 6.2 kcal mol−1; 1,5-dimethylsemibullvalene (2) ΔH≠ = 4.5 kcal mol−1, ΔS≠ = –1.6 cal K−1 mol−1, ΔG≠298 = 5.0 kcal mol−1; 2,6-dibromo-1,5-dimethylsemibullvalene (3) ΔH≠ = 7.5 kcal mol−1, ΔS≠ ≈ 0 cal K−1 mol−1, ΔG≠298 = 7.4 kcal mol−1. The substituent effects are compared with those of other substituted semibullvalenes and are discussed with respect to the nature of the transition state for the Cope rearrangement of bridged homotropilidenes. The barrier for 2 is the lowest measured so far by dynamic NMR spectroscopy.

Anwendungen der 13C‐NMR‐Spektroskopie, XXVII. Die Aktivierungsparameter der Cope‐Umlagerung von Semibullvalen, 1,5‐Dimethylsemibullvalen und 2,6‐Dibrom‐1,5‐dimethylsemibullvalen

Semibullvalenes. 1. Synthesis and crystal structure of 1,5-dimethyl-2,4,6,8-tetrakis(carbomethoxy)tricyclo[3.3.0.02,8]octa-3,6-diene a donor-acceptor-substituted semibullvalene

Semibullvalenes. 2. A MNDO theoretical study of the rearrangements of semibullvalene and several of its derivatives

Intramolecular Ring-Opening Of Cyclopropanones by Enolate Anions

The synthesis and coordination chemistry of two porphyrin dimers linked either at the 5,5‘ or the 4,4‘ positions of 2,2‘-bipyridine are described. These compounds, which may serve a molecular tectons for the constructions of a variety of supramolecular arrays of diverse function, reveal that the ground- and excited-state electronic communication between the chromophores is only moderately affected by the complexation state of the bipyridyl moiety. The nature of the metal ion chelated by the bipyridine only slightly perturbs the ground-state spectra, and differences observed in the excited state are largely ascribed to the heavy atom effect. This work also shows that conformational changes in structural subunits, in this case induced by bipyridyl complexation of various metal ions, do not necessarily require reorganization of supramolecular systems.

Klaus G. Grohmann

Papers

Anwendungen der 13C‐NMR‐Spektroskopie, XXVII. Die Aktivierungsparameter der Cope‐Umlagerung von Semibullvalen, 1,5‐Dimethylsemibullvalen und 2,6‐Dibrom‐1,5‐dimethylsemibullvalen

Semibullvalenes. 1. Synthesis and crystal structure of 1,5-dimethyl-2,4,6,8-tetrakis(carbomethoxy)tricyclo[3.3.0.02,8]octa-3,6-diene a donor-acceptor-substituted semibullvalene

Semibullvalenes. 2. A MNDO theoretical study of the rearrangements of semibullvalene and several of its derivatives

Intramolecular Ring-Opening Of Cyclopropanones by Enolate Anions

Porphyrins linked directly to the 5,5' positions of 2,2'-bipyridine: a new supramolecular building block and switch.