University of St Andrews

Self‐assembly is emerging as a superior method to prepare adaptive and responsive nanomaterials.  Responsive multivalent interactions are key to such versatile materials. This lecture will highlight soft material composed of cyclodextrins and/or superparamagnetic nanoparticles. It will be shown that using the host‐guest chemistry of cyclodextrins, we can form hydrogels as well as nanocapsules. We can also make “magnetic vesicles” that self‐assemble in microscale linear aggregates in aqueoussolution under the influence of a magnetic field. The metastable linear aggregates can be stabilized by a noncovalent and photoresponsive cross‐linker, which can be photoisomerized between an adhesive and a nonadhesive configuration. Thus, the hybrid material responds to magnetic field as well as to light and a stable self‐assembled structure can only be obtained in a magnetic field in the presence of the noncovalent cross‐linker. We have recently extended this strategy to superparamagnetic nanoparticles modified with cyclodextrin. These hybrid nanoparticles can befurther functionalized using host guest interaction and molecular recognition and they can be used to capture and isolate proteins.

References:1. A. Samanta, B. J. Ravoo, Angew. Chem. Int. Ed. 2014, 53, 12946–12950.2. S. Himmelein, V. Lewe, M. C. A. Stuart, B. J. Ravoo, Chem. Sci. 2014, 5, 1054‐1058.3. J. H. Schenkel, A. Samanta, B. J. Ravoo, Adv. Mater. 2014, 26, 1076–1080.

Current researchPhotochromic metal complexes for the modulation of luminescence and nonlinear optical properties. The ability to switch “ON/OFF” the NLO activity of a molecule is of relevance for the development of molecular photonic devices those properties can be switched by modifying one of the component parts. To achieve an efficient switching effect, the molecule must be stable in the two ON and OFF states and the response time must relatively fast. As most molecules with large quadratic hyperpolarizability values comprise p-systems end-capped with donor and acceptor moieties, various strategies have been proposed such as (i) the alteration of either the electron-donor or the electron-acceptor capacity of the end groups by using redox or protonation/deprotonation external stimuli, and (ii) the alteration of the p-bridge using an external trigger like light, In this latter category photochromic compounds seem to be promising candidates for the design of photoswitchable NLO materials. Among them, dithienylethene (DTE) derivatives are the most promising because of their good fatigue resistance, remarkable thermal stability of both isomers and rapid response time. Typically, DTE undergo reversible interconversion between a non-conjugated open form and a π-conjugated closed form when irradiated in the UV and visible spectral ranges, respectively, and changes in the p-conjugated chain of DTE derivatives can be successfully used to control donor-acceptor interactions. Photochromic interconversion of a dithienylethene (DTE) unit Our research group has  been studying the NLO and luminescence properties of bipyridyl metal complexes. We have for example shown that compounds such as donor-substituted bipyridines are excellent building blocks for the construction of either dipolar compounds or non-dipolar (octupolar) metal complexes of D3 and D2d symmetry. More recently, we have alsoinvestigated the luminescent, sensing and NLO properties of square planar yclometallatedPt(II) complexes featuring acetylacetonate or alkynyl ligands.Photochromic organometallic and coordination compounds can be used for thephotomodulation of the quadratic nonlinear optical (NLO) properties, as well as for thephotoswitching of the luminescence properties of the resulting complexes. To this end, we have designed new chromophores combining dithienylethene units and bipyridine or alkynyl ligands with different organometallic fragments (ZnII, IrIII, FeII, RuII, ReI…) giving rise to photochromic metal complexes containing from one to six DTE units, and studied the photocontrol of both NLO and luminescence properties.

Both the problems of the global warming and shortage of the fossil fuels have brought about great interest in photochemical utilization of CO2 with solar energy.   Efficient photocatalysts for CO2 reduction must be necessary for development of such an important technology.

We have developed novel types of photocatalytic systems using metal complexes and/or semiconductors as a photocatalyst.1   In this presentation, I will focus on the architecture of two types of the photocatalysts using transition metal complexes:

(1) A mixed photocatalytic system including a ring-shaped Re(I) multinuclear complex as a photosensitizer2

(2) Ru(II)-Re(I) and Ru(II)-Re(I) supramolecular photocatalysts.3

The efficiency of the former photocatalytic system has been highest in the reported CO2-reduction photocatalysts ( = 82%), and the latter photocatalysts have been most robust (TON > 3000).

2015 Holweck Prize Lecture

Joint Physics/Chemistry Colloquium

The emergence of molecular photonics at the cross-roads of physics, chemistry and device engineering has being triggered by increasing demand in various fields such as high bitrate telecommunications, sensors, and bio-imaging. The wealth of molecular structures and the exploitation of their functional and structural flexibility opens-up new, exciting horizons for this area of research. Designing highly efficient molecules with optimised photonic properties remains a major challenge after 50 years of continuous development, based on fruitful and interdisciplinary cooperation between chemists and physicists.

In this lecture, the principles of molecular engineering for quadratic nonlinear optics will be discussed, with an emphasis on metal complexes and lanthanide derivatives, on nonlinear optical characterization methods. This will be followed by a review of intermolecular interactions and various orientation methods, in order to bridge the gap between molecules to materials, towards a wide range of applications. Finally, perspectives will be provided on molecular photonics towards device–rel.

The talk will last for 50 minutes, starting at 3.00 pm and finishing at 3.50 pm.

Multiferroics are crystals that simultaneously exhibit ferromagnetism and ferroelectricity (and usually ferroelasticity, which is hysteretic stress/strain).  In some cases the ferromagnetism is actually created by the ferroelectricity, by causing the spins to cant [via Dzyaloshinskii-Moriya anisotropic exchange: P.(L x M)].  These materials have become very popular in part due to the interesting new physics, previously neglected because the effects require very low crystal symmetry, and because they offer the promise of new kinds of memory devices, including voltage-tunable magnetic tunnel junctions and four-state memories (+P,+M; +P,-M; -P,+M; -P,-M) which would be vastly superior to the usual binary (0,1) Boolean algebra. At St. Andrews I am experimentally studying GaFeO3 and Pb[Fe(1/2)Ta(1/2)]y[Ti(1/2)Zr(1/2)(1-y)]O3.