Porphyrin‐Based Molecular Rotors as Fluorescent Probes of Nanoscale Environments

Abstract

The synthesis, characterization, and photophysical properties of a series of supramolecular triads consisting of a tin(IV) porphyrin with axial ligands of ortho‐, meta‐, and para‐hydroxyphenyl naphthalenediimides are presented. For the meta‐ and para‐hydroxyphenyl derivatives, efficient and solvent‐viscosity‐dependent quenching of porphyrin fluorescence is observed. Experimental and theoretical studies demonstrate that, in these compounds, photoinduced electron transfer from the phenolate to the porphyrin is modulated by large amplitude rotational motions of the naphthalenediimide. These compounds are novel examples of fluorescent molecular rotors, and their potential use as environmental probes of local viscosity and temperature are discussed.

Fluorescence Anisotropy of Molecular Rotors

“…This has allowed for their successful implementation in fluorescence lifetime imaging (FLIM) to map intracellular microviscosity. Fluorescent molecular rotors based on porphyrins can also probe local environments [49] and a novel ratiometric molecular rotor based on the conjugated porphyrin dimer structure has been used to monitor changes in local viscosity during cell death. [50] In this case, due to the ratiometric "readout" from the probe based on spectral measurements, the result was independent of local concentration of the fluorophore.…”

Sensing membrane stress with near IR-emissive porphyrins

“…This sensitivity to physical environmental changes indicates that molecular rotors can be used more broadly to sense changes in material cohesion and stability as well. Recently, porphyrin-based molecular rotors have gained interest due to their potential for functionalization and incorporation into more complex structures (6,7). In addition, mesoto-meso ethyne-bridged (porphinato)zinc(II) oligomers (PZn n compounds) investigated by Duncan et al (8) demonstrate exceptional near-infrared (NIR) fluorescence, furthering their potential as in vivo stress probes.…”

Molecular Rotors as Fluorescent Viscosity Sensors: Molecular Design, Polarity Sensitivity, Dipole Moments Changes, Screening Solvents, and Deactivation Channel of the Excited States

“…For traditional FMRs, such as 4-(dicyanovinyl)julolidine (2; Scheme 1), the maximum x values is about 0.6. [5] log I = C + x log η (1) Although preliminary studies on FMRs are promising, the present molecular rotors suffer from significant limitations, [5] (1) the FMR structure is restricted to 2 and its close derivatives, [5,7,10,11,25] since very few rotors with different fluorophores are known; [8,13,26,27] (2) the photophysical properties of the present rotors are poor, for example, short excitation/emission wavelength (ca. 460 nm/500 nm for FMR 1 and 2), small Stokes shifts (ca.…”