Fluorescence properties of a novel homodimeric BODIPY dye rotor for Fluorescence Lifetime Imaging Microscopy (FLIM) are reported. Steady state and time resolved fluorescence measurements established the viscosity dependent behaviour in vitro. Homodimeric BODIPY embedded in different membrane mimicking lipid vesicles (DPPC, POPC and POPC plus cholesterol) is demonstrated to be a viable sensor for fluorescence lifetime based viscosity measurements. Moreover, SKOV3 cells readily endocytosed the dye, which accumulated in membranous structures inside the cytoplasm thereby allowing viscosity mapping of internal cell components.

Styryl dyes, specifically LDS group dyes, are known solvatochromic and electrochromic probes for monitoring mitochondrial potential in cellular environments. However, the ability of these dyes to respond to fluctuations in viscosity, pH and temperature has not been established. In this study, we demonstrated that LDS 798 (also known as Styryl-11) can sense environmental viscosity (via fluorescence lifetime changes) as well as pH changes (ratiometric intensity change) in the absence of polarity variations. Polarity changes can be probed by spectral changes using LDS 798. Therefore, all properties of the media should be considered, when these types of dyes are used as electrochromic/solvatochromic sensors in cellular environments.

Photophysical behaviour of a novel trimeric BODIPY rotor with a high extinction coefficient is reported.

The fluorescent lifetimes of the BODIPY–BODIPY dyad appear to correlate with the viscosity of the media, thus making this rotor a suitable small molecule viscometer.

Stretching of the polymer film induces a conformational change in the embedded porphyrin dimer.