Spectral, Conformational and Photochemical Analyses of Photochromic Dithienylethene:cis-1,2-Dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene Revisited

Real-time precision opto-control of chemical processes in live cells

Precision control of molecular activities and chemical reactions in live cells is a long-sought capability by life scientists. No existing technology can probe molecular targets in cells and simultaneously control the activities of only these targets at high spatial precision. We develop a real-time precision opto-control (RPOC) technology that detects a chemical-specific optical response from molecular targets during laser scanning and uses the optical signal to couple a separate laser to only interact with these molecules without affecting other sample locations. We demonstrate precision control of molecular states of a photochromic molecule in different regions of the cells. We also synthesize a photoswitchable compound and use it with RPOC to achieve site-specific inhibition of microtubule polymerization and control of organelle dynamics in live cells. RPOC can automatically detect and control biomolecular activities and chemical processes in dynamic living samples with submicron spatial accuracy, fast response time, and high chemical specificity.

There is a need to control molecular activities at high spatial precision. Here the authors report a real-time precision opto-control technology that detects a chemical-specific optical response from molecular targets, and precisely control photoswitchable microtubule polymerization inhibitors in cells.

In situ illumination with inelastic neutron scattering: a study of the photochromic material cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene (CMTE)

For the first time we successfully demonstrate in situ illumination of a photochromic material during an inelastic neutron scattering (INS) experiment at cryogenic temperatures. cis-1,2-Dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene (CMTE) is a well-studied and commercially available photochromic compound that undergoes a cyclisation reaction when exposed to light with a wavelength of around 400 nm. CMTE was therefore used as a proof of concept material to demonstrate the new sample environment used on the TOSCA indirect geometry spectrometer. When combined with simulated INS spectra from DFT calculations, the resulting difference spectra were interrogated to obtain insight into how the photoisomerisation affects the vibrational modes of the material. It was found that rigidification of the molecule after illumination, caused by the cyclisation of the central six-membered ring in CMTE, led to a blue-shifting in the methyl group torsion modes as well as methyl group scissor modes.

Photochemical multivariate curve resolution models for the investigation of photochromic systems under continuous irradiation

We propose a multivariate curve resolution approach for the investigation of photochromic systems using UV-Visible spectroscopy. The incorporation of photochemical hard-models as constraints in multivariate curve resolution alternating least squares (MCR-ALS) allows extracting reaction quantum yields in situations where a complete knowledge of the system is not available. We apply this approach to the study of the photochromism of CMTE (cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene) under continuous monochromatic irradiation. The mechanism, involving 3 species and 2 reversible reactions, is written and translated into a kinetic constraint that can be applied to the concentration profiles within ALS. First, ambiguity of the solution obtained for photochemical model(s) is calculated and discussed for single set analysis. Multiset analysis is then proposed combining data obtained under different irradiation wavelengths to provide more reliable results. Finally, the photochemical reactivity of CMTE is widely unraveled, and some description of the mechanism observed under irradiation at 365 nm is given.

Excited-State Electronic Asymmetry Prevents Photoswitching in Terthiophene Compounds

The diarylethene moiety is one of the most extensively used switches in the field of molecular electronics. Here we report on spectroscopic and quantum chemical studies of two diarylethene-based compounds with a non- C₃-symmetric triethynyl terthiophene core symmetrically substituted with RuCp*(dppe) or trimethylsilyl termini. The ethynyl linkers are strong IR markers that we use in time-resolved vibrational spectroscopic studies to get insight into the character and dynamics of the electronically excited states of these compounds on the picosecond to nanosecond time scale. In combination with electronic transient absorption studies and DFT calculations, our studies show that the conjugation of the non- C₃-symmetric triethynyl terthiophene system in the excited state strongly affects one of the thiophene rings involved in the ring closure. As a result, cyclization of the otherwise photochromic 3,3″-dimethyl-2,2':3',2″-terthiophene core is inhibited. Instead, the photoexcited compounds undergo intersystem crossing to a long-lived triplet excited state from which they convert back to the ground state.