Shiming Li

Photoswitched DNA-Binding of a Photochromic Spiropyran

The dramatically different DNA-binding properties of the two isomeric forms of a photochromic spiropyran have been demonstrated, enabling photoswitched DNA binding. The closed, UV-absorbing form shows no signs of interaction with DNA. Upon UV exposure the spiropyran is isomerized to the open form that binds to DNA by intercalation. The process is fully reversible as the corresponding dissociation process is induced by visible light.

Photochromic supramolecular memory with nondestructive readout.

Looking without touching: The light-controlled isomerization of a complex containing a pyridine-appended dithienylethene (DTE; green) and a porphyrin dimer induces dramatic structural and spectral changes (see picture). These changes are monitored in a region outside the photochromically active absorption bands of DTE, therefore allowing a nondestructive readout so that the process functions as a molecular optically controlled memory.

An All-Photonic Molecule-Based D Flip-Flop

The photochromic fluorescence switching of a fulgimide derivative was used to implement the first molecule-based D (delay) flip-flop device, which works based on the principles of sequential logic. The device operates exclusively with photonic signals and can be conveniently switched in repeated cycles.

Molecular Implementation of Sequential and Reversible Logic Through Photochromic Energy Transfer Switching

Photochromic spiropyrans modified with fluorophores were investigated as molecular platforms for the achievement of fluorescence switching through modulation of energy transfer. The dyads were designed in such a way that energy transfer is only observed for the open forms of the photochrome (merocyanine and protonated merocyanine), whereas the closed spiropyran is inactive as an energy acceptor. This was made possible through a deliberate choice of fluorophores (4-amino-1,8-naphthalimide, dansyl, and perylene) that produce zero spectral overlap with the spiro form and considerable overlap for the merocyanine forms. From the Förster theory, energy transfer is predicted to be highly efficient and in some cases of 100% efficiency. The combined switching by photonic (light of λ>530 nm) and chemical (base) inputs enabled the creation of a sequential logic device, which is the basic element of a keypad lock. Furthermore, in combination with an anthracene-based acidochromic fluorescence switch, a reversible logic device was designed. This enables the unambiguous coding of different input combinations through multicolour fluorescence signalling. All devices can be conveniently reset to their initial states and repeatedly cycled.

An All-Photonic Molecule-Based Parity Generator/Checker for Error Detection in Data Transmission

The function of a parity generator/checker, which is an essential operation for detecting errors in data transmission, has been realized with multiphotochromic switches by taking advantage of a neuron-like fluorescence response and reversible light-induced transformations between the implicated isomers.

Molecular AND-logic for dually controlled activation of a DNA-binding spiropyran

A spiropyran photoswitch is activated using UV light and protons from a form that shows no interaction with DNA to a form that binds to DNA by intercalation. This scheme is interpreted as a biologically relevant logic AND gate with potential applications as a dually controlled anticancer drug.

Reassignment of relative stereochemistry at C-7 and C-8 in arylcoumaran neolignans

Abstract 1 H NMR spectral characteristics of synthetic trans and cis arylcoumarans and their acetates which are related to 8-5′ neolignans are given. This information is used to reassign structures to neolignans reported in nine papers, from the cis to the trans 7-aryl-8-hydroxymethyl configurations, and to neolignans in six papers in which no assignments were made. Thus far, there is no evidence for the occurrence of 8-5′ neolignans with a cis configuration in nature.

Characterization of the Thermal and Photoinduced Reactions of Photochromic Spiropyrans in Aqueous Solution

Six water-soluble spiropyran derivatives have been characterized with respect to the thermal and photoinduced reactions over a broad pH-interval. A comprehensive kinetic model was formulated including the spiro- and the merocyanine isomers, the respective protonated forms, and the hydrolysis products. The experimental studies on the hydrolysis reaction mechanism were supplemented by calculations using quantum mechanical (QM) models employing density functional theory. The results show that (1) the substitution pattern dramatically influences the pKa-values of the protonated forms as well as the rates of the thermal isomerization reactions, (2) water is the nucleophile in the hydrolysis reaction around neutral pH, (3) the phenolate oxygen of the merocyanine form plays a key role in the hydrolysis reaction. Hence, the nonprotonated merocyanine isomer is susceptible to hydrolysis, whereas the corresponding protonated form is stable toward hydrolytic degradation.

Enantioselective Cyclization of Photochromic Dithienylethenes Bound to DNA

Guiding light: Enantioselectivity is obtained for the photocyclization of a photochromic dithienylethene when isomerization is carried out in the presence of DNA (see scheme). Copyright

Synthesis of cinnamaldehydes, esters of cinnamic acids and acylals of cinnamaldehydes by oxidation of arylpropenes with 2,3-dicyano-5,6-dichlorobenzoquinone (DDQ)

Abstract 1-Arylpropenes and 3-arylpropenes give cinnamaldehydes (yield≈ 80%) on oxidation with 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) in the presence of water. The conversion to aldehydes is promoted by electron-donating groups at the aromatic ring. On DDQ oxidation in the presence of methanol, methyl esters of cinnamic acids are the predominant products. DDQ oxidation of 1- or 3-(3,4-dimethoxyphenyl)-1-propene in the presence of acetic acid gives an acylal [the diacetate of ( E )-3-(3,4-dimethoxyphenyl)-2-propene-1,1-diol].