Give or Take: Effects of Electron-Accepting/-Withdrawing Groups in Red-Fluorescent BODIPY Molecular Rotors

Abstract

Mapping microviscosity, temperature, and polarity in biosystems is an important capability that can aid in disease detection. This can be achieved using fluorescent sensors based on a green-emitting BODIPY group. However, red fluorescent sensors are desired for convenient imaging of biological samples. It is known that phenyl substituents in the β position of the BODIPY core can shift the fluorescence spectra to longer wavelengths. In this research, we report how electron-withdrawing (EWG) and -donating (EDG) groups can change the spectral and sensory properties of β-phenyl-substituted BODIPYs. We present a trifluoromethyl-substituted (EWG) conjugate with moderate temperature sensing properties and a methoxy-substituted (EDG) molecule that could be used as a lifetime-based polarity probe. In this study, we utilise experimental results of steady-state and time-resolved fluorescence, as well as quantum chemical calculations using density functional theory (DFT). We also explain how the energy barrier height (Ea) for non-radiative relaxation affects the probe’s sensitivity to temperature and viscosity and provide appropriate Ea ranges for the best possible sensitivity to viscosity and temperature.

A red-emitting thiophene-modified BODIPY probe for fluorescence lifetime-based polarity imaging of lipid droplets in living cells

“…Such effect achieved by the introduction of electron-withdrawing groups was demonstrated previously. 24 We also note that results presented in Table 1 demonstrate that k nr is significantly faster than k r . Since all of the molecules in this study exhibit only slight solvatochromism (Fig.…”

“…Modifying aand b-positions with aromatic moieties to red-shift the fluorescence wavelength, extinguished the sensitivity to viscosity, whilst increasing responsiveness to polarity. 24 The latter observation was taken in practice by Maleckaite ˙et al who synthesised and explored a red-emitting BODIPY polarity probe BP-PH-OMe modified with electrondonating 4-methoxyphenyl groups at the b,b 0 -positions of the BODIPY core. These results were the basis of this work, where we aimed to synthesise red-emitting polarity probes for sensing in lipid environment.…”

“…This particular aromatic group was chosen because it offers electron-donating capabilities that seem to be connected with increased polarity sensitivity of the BODIPY probes as previously reported. 24 Furthermore, it has been noticed that introduction of electron-rich thienyl groups leads to a large redshift that is crucial for achieving red emission. 25,26 Additionally, long alkoxy chains (-C 10 H 21 and -C 16 H 33 ) were introduced at the para-position of the meso-phenyl ring of our probes that should ensure efficient fit of the probes into the lipid layer.…”

Chitosan Composites Containing Boron-Dipyrromethene Derivatives for Biomedical Applications

“…There are several examples demonstrating the latest achievements in this field, e.g., BODIPY functionalized with lactose [ 21 ], phosphorylated BODIPY [ 22 ], diketopyrrolopyrrole-aza-BODIPY hybrids [ 23 ], N-BODIPY containing a para-nitrophenyl group at the meso position and a diamino-boron substituent with two tosyl pendant moieties [ 24 ], trifluoromethyl-substituted (i.e., with electron-withdrawing groups) and methoxy-substituted (with electron-donating groups) dyes [ 25 ].…”

Exploring BODIPY-Based Sensor for Imaging of Intracellular Microviscosity in Human Breast Cancer Cells

“…A BODIPY core structure in molecular rotors grants large molar extinction coefficients, photostability and chemical inertness [ 17 , 18 , 19 ]. Furthermore, BODIPY-based probes can be easily functionalized at the appropriate positions to tune their sensitivity to micro-environment viscosity, polarity or temperature; increase the emission wavelength or Stokes shift; or direct the molecules to specific cells or organelles [ 20 , 21 , 22 , 23 , 24 , 25 ]. Recently, we demonstrated that the functionalization of meso -phenyl BODIPY (BDP-H) ( Figure 1 ) with a heavy-electron withdrawing –NO 2 group results in a viscosity-sensor with an extremely wide viscosity-sensitivity range (0.5–50,000 cP) [ 21 ].…”