Emission Switching of 4,6-Diphenylpyrimidones: Solvent and Solid State Effects

Alphabet-Inspired Design of (Hetero)Aromatic Push-Pull Chromophores

Push-pull molecules represent a unique and fascinating class of organic π-conjugated materials. Herein, we provide a summary of their recent extraordinary design inspired by letters of the alphabet, especially focusing on H-, L-, T-, V-, X-, and Y-shaped molecules. Representative structures from each class were presented and their fundamental properties and prospective applications were discussed. In particular, emphasis is given to molecules recently prepared in our laboratory with T-, X-, and Y-shaped arrangements based on indan-1,3-dione, benzene, pyridine, pyrazine, imidazole, and triphenylamine. These push-pull molecules turned out to be very efficient charge-transfer chromophores with tunable properties suitable for second-order nonlinear optics, two-photon absorption, reversible pH-induced and photochromic switching, photocatalysis, and intercalation.

Novel mono-cationic fluorescent probes based on different central π-conjugated bridges for two-photon bioimaging of cellular nuclei

A series of novel pyridine mono-cationic two-photon fluorescent probes based on different central π-conjugated bridges, fluorenone (W-pyI), dibenzothiophene (S-pyI), and dibenzofuran (F-pyI), were prepared and studied for improving photostability in bioimaging applications.

Position of Substitution: A Facile Way to Tune the Spectroscopic Properties of Dimethylamino-Substituted Arylene-Ethynylenes

A series of dimethylamino-substituted arylene-ethynylenes were synthesised by Sonogashira coupling reactions and characterised by the methods of 1H, 13C NMR, UV-Vis, fluorescence, HRMS and theoretical calculations. Effects on spectroscopic properties caused by the different positions of the dimethylamino group in arylene-ethynylenes were studied and discussed. The shortest absorption maximum, the largest Stokes shift and the highest fluorescence efficiency were observed for arylene-ethynylenes with a dimethylamino group present in the ortho-position.

Photophysics and rotational diffusion of hydrophilic molecule in polymer and polyols

In this work we report the photophysics and rotational diffusion of a hydrophilic solute 7-(N,N'-diethylamino)coumarin-3-carboxylic acid (7-DCCA) in four protic solvents: poly(ethylene glycol), ethylene glycol, tetraethylene glycol, and glycerol, with variation of temperature. The cumulative effect of polarity, viscosity, and structural features of these solvents, as well as specific solute-solvent interaction on the photophysical properties of 7-DCCA was discussed. We observed significant differences in both steady-state and time-resolved emission properties. Estimation of activation energy of viscous flow and activation energy of nonradiative decay reinforce our assumption of a cumulative effect. It was observed that, in all solvents, H-bonding interactions are mainly responsible for changing the spectral properties. Study of rotational relaxation behavior demonstrates superstick boundary condition to be operative in ethylene glycol. It is due to the H-bonding interaction between 7-DCCA and ethylene glycol. Similarly, stick boundary condition is followed in case of tetraethylene glycol at 278 K and further from 293 K. Convergence to the stick boundary is observed in case of poly(ethylene glycol). These changes can be attributed to the change in structural organization in both poly(ethylene glycol) and tetraethylene glycol.

Turn-on, fluorescent nuclear stains with live cell compatibility

DNA-binding, green and yellow fluorescent probes with excellent brightness and high on/off ratios are reported. The probes are membrane permeable, live-cell compatible, and optimally matched to 405 nm and 514 nm laser lines, making them attractive alternatives to UV-excited and blue emissive Hoechst 33342 and DAPI nuclear stains. Their electronic structure was investigated by optical spectroscopy supported by TD-DFT calculations. DNA binding is accompanied by 27- to 75-fold emission enhancements, and linear dichroism demonstrates that one dye is a groove binder while the other intercalates into DNA.