Justyna M. Żurek

Gelation Landscape Engineering Using a Multi-Reaction Supramolecular Hydrogelator System

Simultaneous control of the kinetics and thermodynamics of two different types of covalent chemistry allows pathway selectivity in the formation of hydrogelating molecules from a complex reaction network. This can lead to a range of hydrogel materials with vastly different properties, starting from a set of simple starting compounds and reaction conditions. Chemical reaction between a trialdehyde and the tuberculosis drug isoniazid can form one, two, or three hydrazone connectivity products, meaning kinetic gelation pathways can be addressed. Simultaneously, thermodynamics control the formation of either a keto or an enol tautomer of the products, again resulting in vastly different materials. Overall, this shows that careful navigation of a reaction landscape using both kinetic and thermodynamic selectivity can be used to control material selection from a complex reaction network.

Vibronic coupling in inorganic systems: Photochemistry, conical intersections, and the jahn-teller and pseudo-jahn-teller effects

Abstract Vibronic coupling effects in inorganic systems are of great importance in a variety of scientific fields. Such effects involve a breakdown of the Born–Oppenheimer approximation and the separation of electronic and nuclear motion. We present the basic background theory involved in this, including a discussion of conical intersections, Jahn–Teller vibronic coupling, and pseudo-Jahn–Teller vibronic coupling. In addition to reviewing the importance of vibronic coupling in photochemistry in general, we also review some of the more important computational contributions to inorganic photochemistry. By way of examples, we present several case studies from our own recent work highlighting the issues involved in computational modeling of vibronic coupling effects in inorganic chemistry. These include the computation of coupled Jahn–Teller potential energy surfaces in binary transition metal carbonyl photodissociation, and ultrafast radiationless relaxation of the generated unsaturated metal carbonyl; semi-classical and quantum wave packet dynamics simulations of this relaxation process; analysis of the pseudo-Jahn–Teller effect in ammonia, and an edge-sharing bimetallic bioctahedral complex; and finally the photochemical izomerization of a platinum–amido pincer complex from mer to fac that involves a general nonsymmetry imposed conical intersection along the reaction path.

Photoracemization and excited state relaxation through non-adiabatic pathways in chromium (III) oxalate ions.

Computational studies on the photochemistry of the open-shell chromium oxalate [Cr(C(2)O(4))(3)](3-) ion, including its non-adiabatic relaxation pathways, have been performed. The presence of the peaked conical intersection of a quasi-Jahn-Teller type, connecting the (4)T state with (4)A(2) ground state, accounts for the observed photoinduced racemization. This involves the rupture of one of the Cr-O bonds and the complex forms an unstable trigonal bipyramid form that connects both ground state stereoisomers with the excited quartet manifold. Intersystem crossing seams have been located between the (4)T and lower lying (2)E state which can quench the quartet reaction and lead to (2)E → (4)A(2) emission.

Photostereochemistry and photoaquation reactions of [Cr(tn)3]3+: theoretical studies show the importance of reduced coordination conical intersection geometries.

We have performed TD-DFT and CASSCF calculations to understand the spectroscopy and reactive photochemistry of the [Cr(tn)(3)](3+) complex. Our results show that, after population of a quartet ligand field excited state, the system relaxes by dissociation of a Cr-N bond to reach a quasi-trigonal bipyramid five-coordinate species that is a conical intersection connecting the excited and ground quartet manifolds. Nonadiabatic relaxation through these leads to square pyramidal structures that can coordinate water and account for the observed monoaquated photoproducts. Such features are also present on the potential energy surfaces of these photoproducts and account for the range of experimentally observed photostereoisomers of the photoaquation reactions.

Unusual Structure-Energy Correlations in Intramolecular Diels–Alder Reaction Transition States

Detailed analysis of calculated data from an experimental/computational study of intramolecular furan Diels–Alder reactions has led to the unusual discovery that the mean contraction of the newly forming C-C σ-bonds from the transition state to the product shows a linear correlation with both reaction Gibbs free energies and reverse energy barriers. There is evidence for a similar correlation in other intramolecular Diels–Alder reactions involving non-aromatic dienes. No such correlation is found for intermolecular Diels–Alder reactions.

Crossed McMurry Coupling Reactions for Porphycenic Macrocycles: Non-Statistical Selectivity and Rationalisation

Crossed McMurry reactions of bifuran- or bithiophenedicarbaldehydes with bipyrroledicarbaldehydes have been studied for the first time. Only those porphycenic macrocycles derived from homocoupled McMurry products were formed. The results are explained by using both density functional theory and electron propagator computations to model the electron affinity of the dialdehyde starting materials. It was predicted that bifuran\bithiophene cross-coupling would indeed occur, and this was demonstrated by the first synthesis of a novel dioxa,dithio hetero-porphycenoid annulene. This approach will allow the prior identification of viable substrates for related crossed McMurry reactions.

Intramolecular Nitrofuran Diels–Alder Reactions: Extremely Substituent-Tolerant Cycloadditions via Asynchronous Transition States

Nitrofurans undergo intramolecular Diels-Alder reactions with tethered electron-poor dienophiles more rapidly and in higher yield than non-nitrated furans. Computational studies indicate that increased stabilization of a partial positive charge on the nitro-substituted carbon in both transition state and product is the driving force for these reactions. Frontier molecular orbital energy differences indicate a switch from normal to inverse electron demand upon nitration. There does not appear to be a contribution from any differences in aromatic stabilization energy between furans and nitrofurans. Calculations show that the nitrofuran reactions proceed via a highly asynchronous transition state allowing easier bond formation between two sterically hindered carbons.