Thiophene‐Inserted Aryl–Dicyanovinyl Compounds: The Second Generation of Fluorescent Molecular Rotors with Significantly Redshifted Emission and Large Stokes Shift

Abstract

Fluorescent molecular rotors can be used as molecular sensors for the viscosity of a microenvironment. However, these molecular rotors are limited to 9‐(dicyanovinyl)julolidine (DCVJ) and a few derivatives. Furthermore, these traditional rotors show short absorption/emission wavelengths and small Stokes shifts. To address these drawbacks, we have developed a small library of new molecular rotors for viscosity sensing, prepared by incorporating a thiophene unit into the conventional fluorescent molecular rotors with the aim of accessing molecular rotors with redshifted excitation/emission wavelengths and larger Stokes shifts compared with the known rotors. The new rotors show substantially improved photophysical properties. For example, rotor 4 shows absorption/emission wavelengths of 559/697 nm, respectively, and a very large Stokes shift of 138 nm compared with the absorption/emission wavelengths (465/503 nm) and very small Stokes shift (38 nm) of the traditional fluorescent molecular rotor DCVJ. The photophysical properties of the rotors were rationalized by DFT calculations.

A “Distorted‐BODIPY”‐Based Fluorescent Probe for Imaging of Cellular Viscosity in Live Cells

“…where η is the viscosity, I is the emission intensity, C is a constant, and x is the sensitivity of the probe to viscosity. 5h BV‐1 fits the linear relationship between log I and log η ( R 2 =0.99). Importantly, the x value is as high as 0.62 (Figure 1 b).…”

“…4, 5 Recently, significant efforts have been devoted to the development of different kinds of FMRs. However, typical molecular rotors, which are a special subgroup of twisted intramolecular charge transfer (TICT) fluorophores, are more or less sensitive to the solvent polarity;4b, 5a–h porphyrin‐based rotors are synthetically demanding and offer low sensitivity (the fluorescence quantum yield of porphyrins is less than 0.1) 1a. 4a In our previous work, we proved that the rotation of a CHO group at a meso ‐position of a pentamethine cyanine dye is highly sensitive to viscosity 5i.…”

Oligothiophene Amphiphiles as Planarizable and Polarizable Fluorescent Membrane Probes

“…So-called push-pull fluorophores, that is, fluorophores that are equipped with a p donor at one end and a p acceptor at the other, are the leading membrane probes to detect microdomains and membrane potentials. [6][7][8] The deplanarization of push-pull fluorophores in the excited state received much attention in the context of molecular rotors. [5] Push-pull oligothiophenes have further attracted interest for applications in nonlinear optics (NLO), photovoltaics, and biology.…”

“…[3][4][5] Examples include the families around laurdan, Nile red, p-oligophenyls [4] as well as pioneering push-pull oligothiophenes from the Loew research group. [8,9] These fluorophores are used as viscosity sensors and, in pioneering studies, also to report on the fluidity of lipid bilayer membranes. [6][7][8] The deplanarization of push-pull fluorophores in the excited state received much attention in the context of molecular rotors.…”

“…[5] Push-pull oligothiophenes have further attracted interest for applications in nonlinear optics (NLO), photovoltaics, and biology. [6][7][8] The deplanarization of push-pull fluorophores in the excited state received much attention in the context of molecular rotors. [8,9] These fluorophores are used as viscosity sensors and, in pioneering studies, also to report on the fluidity of lipid bilayer membranes.…”