Photoresponsive supramolecular systems: self-assembly of azodibenzoic acid linear tapes and cyclic tetramers

A new strategy to effect photoinduced control over molecular self-assembly is reported. This strategy uses the reversible trans-cis photoisomerization of a novel azobenzene system, where the trans- and cis-forms self-assemble into dramatically different higher-order structures. The trans-azobenzene form of this molecule associates into infinite hydrogen-bonded linear tapes, while the cis-azobenzene form undergoes hydrogen-bonded self-assembly into cyclic tetramers. This results in a second level of association, where the cis-hydrogen-bonded supramolecular cycles ultimately form long, rod-like aggregates through stacking interactions.     

A theoretical study of solvation energies of FCH2COO−, FCH2COOH,and F2CHCOO−

A continuum and a discrete-continuum models are used to determine the solvation energies of FCH₂COO^?, FCH₂COOH, and F₂CHCOO^?. For the anions, the continuum model provides results closer to the experiment, while for the acid, the addition of one water molecule improves the continuum-only energy.     

Ozonization: An Efficient Method for the Oxidation of Halophosphines

Abstract

The ozonization of various halophosphines 1a-j leads with quantitative yields to the corresponding phosphine oxides 2a-j.

Ozonization is a convenient method of oxidation, in particular of compounds with bulky ligands (1c, 1d, 1e).     

Bottleable Neutral Analogues of [B2H5]− as Versatile and Strongly Binding η2 Donor Ligands

Herein we report the discovery that two bottleable, neutral, base‐stabilized diborane(5) compounds are able to bind strongly to a number of copper(I) complexes exclusively through their B?B bond. The resulting complexes represent the first known complexes containing unsupported, neutral σ_B?B diborane ligands. Single‐crystal X‐ray analyses of these complexes show that the X?Cu moiety (X=Cl, OTf, C₆F₅) lies opposite the bridging hydrogen atom of the diborane and is near perpendicular to the B?B bond, interacting almost equally with both boron atoms and causing a B?B bond elongation. DFT studies show that σ donation from and π backdonation to the pseudo‐π‐like B?B bond account for their formation. Astoundingly, these copper σ_B?B complexes are inert to ligand exchange with pyridine under either heating or photoirradiation.     

The specific contribution of phosphorus in dendrimer chemistry

Besides properties commonly found for all types of dendrimers, phosphorus-containing dendrimers possess some specific properties seldom or never found for other types of dendrimers. Emphasis will be put on these specificities.     

List of subject

We report the high resolution emission (S₁ → S₀, T₁ → S₀) and laser single site singlet excitation (S₁ ← S₀) spectra for the various insertion sites of coronene in n-heptane cooled to 1.5 K. The observation of site splitting of doubly degenerate vibrations and weak electric dipole forbidden 0, 0 bands in the S₁ → S₀ and T₁ → S₀ spectra indicates that the ground state, the first excited singlet and lowest triplet states are all distorted. In these spectra, the intensity distribution of the various sites in the 0, 0 bands suggests that the distortion is different from site to site but similar in S₀, S₁ and T₁. Identical ordering of the sites in S₁ S₀ and S₁ S₀ spectra as well as the observation of weak shifts in the vibrational frequencies in the two states implies the absence of strong pseudo Jahn-Teller forces in the first excited singlet state. We propose, further, that this is also true for the triplet state. This conclusion is supported by the similarity in zero-field splitting parameters of coronene and deuterated coronene. Taken together, these results indicate strongly that the distortion of coronene in n-heptane is primarily crystal field induced and is not greatly changed upon excitation of the molecule to its lowest excited states.