Diarylethene Photoswitches Research Articles

Molecular design strategy toward diarylethenes that photoswitch with visible light.

Photoactive molecules that reversibly switch upon visible light irradiation are one of the most attractive targets for biological as well as imaging applications. One possible approach to prepare such photoswitches is to extend π-conjugation length of molecules and shift the absorption bands to longer wavelengths. Although several attempts have been demonstrated based on this approach for diarylethene (DAE) photoswitches, photoreactivity of the DAE derivatives is dramatically suppressed when the conjugation length is extended by connecting aromatic dyes at the side positions of aryl groups in the DAE unit. In this study, we successfully prepared a visible-light reactive DAE derivative by introducing an aromatic dye at the reactive carbon atom of the DAE unit, optimizing orbital level of each component, and controlling the mutual orientation of the aromatic dye and the DAE unit. The DAE derivative (3) undergoes a photocyclization reaction upon irradiation with 560 nm light and the closed-isomer converts to the open-ring isomer upon irradiation with 405 nm light. The high photoconversion yields (>90%) were achieved for both photocyclization and photocycloreversion reactions. The photoreactivity induced by visible light irradiation and the molecular design strategy were discussed based on theoretical calculations.

Communication through molecular bridges: different bridge orbital trends result in common property trends.

Common trends in communication through molecular bridges are ubiquitous in chemistry, such as the frequently observed exponential decay of conductance/electron transport and of exchange spin coupling with increasing bridge length, or the increased communication through a bridge upon closing a diarylethene photoswitch. For antiferromagnetically coupled diradicals in which two equivalent spin centers are connected by a closed-shell bridge, the molecular orbitals (MOs) whose energy splitting dominates the coupling strength are similar in shape to the MOs of the dithiolated bridges, which in turn can be used to rationalize conductance. Therefore, it appears reasonable to expect the observed common property trends to result from common orbital trends. We illustrate based on a set of model compounds that this assumption is not true, and that common property trends result from either different pairs of orbitals being involved, or from orbital energies not being the dominant contribution to property trends. For substituent effects, an effective modification of the π system can make a comparison difficult.

Electron transport properties of diarylethene photoswitches by a simplified NEGF-DFT approach.

A homemade program called FOXY has been used for the theoretical investigation on the conducting properties of two diarylethene based molecules, which, according to recent literature data, can act as photoswitches. FOXY uses a simplified method relying on NEGF theory coupled to DFT calculations and using a suitable electric field to mimic the bias voltage, together with a simple representation of the electrodes. The results confirm the experimental findings and are rationalized by analyzing the space extension of the pertinent molecular orbitals in the ON and OFF electronic states and confirm the FOXY program as a cheap and reliable code to be used in the field of molecular electronics.

Photocontrol of luminescent inorganic nanocrystals via an organic molecular switch.

A photo-controlled and quasi-reversible switch of the luminescence of hexadecylamine-coated ZnO nanocrystals (ZnO@HDA Ncs) is operated via a molecular photoswitch (dithienylethene, DTE). The interaction between the DTE switch and the ZnO@HDA Ncs is thoroughly investigated using NMR spectroscopy techniques, including DOSY and NOESY, showing that the DTE switch is weakly adsorbed at the surface of the Ncs through the formation of hydrogen bonds with HDA. Steady state and time-resolved luminescence quenching experiments show a complex behavior, related to the spatial distribution of the emitting defects in the Ncs. Analysis of the data using models previously developed for Ncs supports static quenching. Both isomeric forms (open or closed) of the DTE switch quench the emission of Ncs, the efficiency being more than ten times higher for the closed isomer. The mechanism of quenching is discussed and we show that quenching occurs mainly through resonant energy transfer for the closed isomer and through electron transfer for the open one. The HDA layer mediates the quenching efficiency as only defects located near the surface are quenched.

A Fully Photoreversible Supramolecular Polymer Having a Diarylethene Photoswitch

Abstract The particle size of a supramolecular polymer composed of a diarylethene photoswitch and two quadruple hydrogen-bonding sites having C17 chain changes photoreversibly in tetrahydrofuran at room temperature, while that in a CHCl3 solution is not photoreversible but is reversible with the assistance of heat.

Novel saccharide tweezers with a diarylethene photoswitch

A photochromic saccharide receptor with a diarylethene photoswitch changes the binding event with glucose by photoirradiation.