Helicenes: synthesis and applications.

Publisher Summary This chapter discusses acid–base properties of electronically excited states of organic molecules. Excited state pK-values are most easily accessible through the use of the Forster cycle. To perform this calculation for a particular molecule, it is necessary to know the ground state equilibrium constant for the reaction in question and to have some measure of the energy difference between the lowest vibrational level of the ground and the excited state in both the B and BH + forms. The effects of solvation on 0–0 energies are discussed. The changes in molecular fluorescence with acidity give information about the protolytic behavior of the excited singlet state of a compound. Two techniques, phase and pulse fluorometry, are used for the direct measurement of fluorescence decay rates. The excited state acid-base behavior of molecules has direct implications in the field of analytical fluorimetry and phosphorimetry.

Acid-Base Properties of Electronically Excited States of Organic Molecules

Carbohelicenes belong to a class of fascinating, chiral, and helicoidal molecules, which have a rich history in chemistry since the very beginning of the 20th century. A renewed interest in polyaromatic chemistry and new synthetic challenges toward the search for innovative physical, biological, chemical and opto-electronic properties have brought high motivation in this field of studies. Theoretical insights gained from polyaromatic, chiral, conjugated and distorted π-systems are also responsible for this development. Several synthetic avenues were originally reported for making lower helicenes, but for many years, photochemical synthesis has remained a major method for producing small amount of helicenes. High-dilution conditions is still a limiting factor in their synthesis. The fulgurous impact of organometallic chemistry, novel synthetic methods, and recent catalytic systems has promoted the development of helicene chemistry, toward a library of tailor-made and highly functionalized helicene molecules. Helicene chemistry is being considered as an expanding and modern field, leading to several applications in supramolecular chemistry, in nanosciences, in chemical-biology, in polymers and materials science. This first part of a series of three reviews on carbohelicenes will be devoted to a comprehensive report on non-stereoselective reactions and methods for producing helicenes, along with their functionalization.

One hundred years of helicene chemistry. Part 1: non-stereoselective syntheses of carbohelicenes.

Theoretical models that have been proposed and applied to proton transfer reactions are reviewed in this work. Simple models, like the Eigen model, Marcus theory and the intersecting state model, are applied to excited-state intermolecular proton transfers. The kinetics and thermodynamics of proton transfers occuring in the singlet states of aromatic molecules with OH, NH3+, NH2 and CO substituents are reviewed.

Excited-state proton transfer reactions I. Fundamentals and intermolecular reactions

Although the effect of solvent on the rate and the position of equilibrium of chemical reactions has been known since the last century, there are still no reliable and exact methods for a quantitative description and prediction of such solvent effects. Empirical parameters of solvent polarity are of great value in this respect and can be derived with the aid of the principle of “linear relationships between free energies” (LFE relationships). The present article deals with the possibilities of establishing reaction and absorption series using solvent-dependent standard reactions or standard absorptions of organic compounds. Particular attention is merited by the summary of the 24 most important empirical parameters of solvent polarity and the table of ET(30) values for 151 solvents. In addition to examples of the application of these values, attempts to improve the LFE correlations of singular empirical parameters of solvent polarity with the aid of multiparametric equations are described.

Empirical Parameters of Solvent Polarity as Linear Free‐Energy Relationships

Synthesis of heptahelicene (1) benzo [c] phenanthro [4, 3-g ]phenanthrene.

Substitution électrophile sur carbone saturé: III. Compétition entre les effets stériques et inductifs en fonction de la polarité du solvant lors de l'action des halogénes sur les tétraalkyllétains

Determination des valeurs pKa des formes protonees des trois complexes de TAP dans leur etat fondamental et dans le premier etat excite de transfert de charge. On observe un declin de luminescence par des tampons organiques dans des domaines de pH ou la protonation ne peut avoir lieu; attribution a la formation de liaisons hydrogene entre l'acide carboxylique du tampon et l'un des atomes d'azote libres du coordinat TAP

Ruthenium(II) complexes of 1,4,5,8-tetraazaphenanthrene (TAP) and 2,2'-bipyridine (bpy). Ground- and excited-state basicities of Ru2+(bpy)n(TAP)3-n (n = 0,1,2): their luminescence quenching by organic buffers

Jacques Nasielski

Papers

Synthesis of heptahelicene (1) benzo [c] phenanthro [4, 3-g ]phenanthrene.

Substitution électrophile sur carbone saturé: III. Compétition entre les effets stériques et inductifs en fonction de la polarité du solvant lors de l'action des halogénes sur les tétraalkyllétains

Ruthenium(II) complexes of 1,4,5,8-tetraazaphenanthrene (TAP) and 2,2'-bipyridine (bpy). Ground- and excited-state basicities of Ru2+(bpy)n(TAP)3-n (n = 0,1,2): their luminescence quenching by organic buffers

Photo-induced hydrogenation of conjugated dienes catalyzed by chromium hexacarbonyl

Mécanismes de rupture de la liaison carbone-ðain par les halogens I. Substitution électrophile sur carbone saturé