Sila-and germa uorenes containing alkynyl(aryl) substituents at the 2,7-position are strongly emissive with high quantum yields in organic solvents. Provided they are su ciently soluble in water, their hydrophobic structures have the potential for many biological and industrial applications in the detection and characterization of lipophilic structures. To that end, the emission behaviors of previously synthesized 2,7-bis[alkynyl(biphenyl)]-9,9-diphenylsila uorene (1), 2,7-bis[alkynyl(methoxynaphthyl)]-9,9diphenylgerma uorene (2), 2,7-bis[alkynyl(p-tolyl)]-9,9-diphenylsila uorene (3), and 2,7-bis[alkynyl(muorophenyl)]-9,9-diphenylsila uorene (4) were characterized in aqueous solution and in the presence of various surfactants. Despite a high degree of hydrophobicity, all of these metalla uorenes (MFs) are soluble in aqueous solution at low micromolar concentrations and luminesce in a common aqueous buffer. Further, the 2,7 substituent makes the emission behavior tunable (up to 20 nm). Fold emission enhancements in the presence of various surfactants are highest toward Triton X-100 and CTAB (ranging from 5-25 fold) and are lowest for the anionic surfactants SDS and SDBS. These enhancements are competitive with existing probes of surfactants. Quantum yields in buffer range from 0.11 to 0.34, competitive with many common uorophores in biological use. Strikingly, MF quantum yields in the presence of TX-100 and CTAB approach 100% quantum e ciency. MF anisotropies are dramatically increased only in the presence of TX-100, CTAB, and CHAPS. Coupled with the above data, this suggests that MFs associate with neutral and charged surfactant aggregates. Interactions with the anionic surfactants are weaker and/or leave MFs solvent exposed. These properties make metalla uorenes competitive probes for surfactants and their properties and behaviors, and thus could also have important biological applications.

Fluorescent compounds have been shown to be useful in probing lipid dynamics, and there is ongoing interest in nontoxic, photostable, and sensitive dyes. Recently, we evaluated a number of 2,7-disubstituted-alkynyl(aryl)-3,6-dimethoxy-9,9-diphenyl sila- and germafluorenes for their potential as cellular fluorescent probes. These compounds exhibit remarkable quantum yields in hydrophobic environments and dramatic increases in emission intensity in the presence of surfactants. Here, we show that they exhibit significant emission enhancements in the presence of small unilamellar vesicles and are nontoxic to E. coli, S. aureus, and S. cerevisiae. Furthermore, they luminesce in S. cerevisiae cells with strong photostability and colocalize with the lipid droplet stain Nile Red, demonstrating their promise as lipid probes.

Push–pull dyes exhibit intramolecular charge transfer behavior, which due to changes in the dipole moment upon excitation, is the origin of their sensitivity to the environment. Such compounds are of interest as probes for bioimaging and as biosensors to monitor cellular dynamics and molecular interactions. Desirable biological probes absorb in the visible region, have high extinction coefficients, high quantum yield and excellent photostability. Fluorophores with scaffolding that can be used to tune and optimize solvatochromic behavior are of particular interest. Here, we investigate the environmental sensitivity of a small library of highly fluorescent 2,7-disubstituted sila- and germafluorenes. Density functional theory (DFT) calculations show that charge transfer occurs from the alkyne core out to the 2,7-substitutents and 3,6-methoxy substituents, the hallmark of push–pull behavior. They exhibit HOMO–LUMO energy gaps of about 3 eV with desirable dipole moments ranging from 2 to 9 D. These compounds exhibit desirable Stokes shifts in various solvents (25 to 102 nm). Interestingly, silafluorene with a benzaldehyde substituent exhibits competitive solvatochromic behavior. With the ability to tune push–pull properties via the 2,7-substituent, these disubstituted sila- and germafluorenes have excellent potential as biological probes.

Push-pull dyes exhibit intramolecular charge transfer behavior, which due to changes in dipole moment upon excitation, is the origin of their environmental sensitivity. Such compounds are of interest as probes for bioimaging and as biosensors to monitor cellular dynamics and molecular interactions. Desirable biological probes absorb in the visible region, have high extinction coefficients, high quantum yields and excellent photostability. Fluorophores with scaffolding that can be used to tune and optimize solvatochromic behavior are of particular interest. Here we investigate the environmental sensitivity of a small library of highly fluorescent 2,7-disubstituted sila- and germafluorenes. Density functional theory calculations show that charge transfer occurs from the alkyne core out to the 2,7- and 3,6-methoxy substituents, the hallmark of push-pull behavior. They exhibit HOMO-LUMO energy gaps of about 3 eV with dipole moments ranging from 2-3.25 D. These compounds exhibit desirable Stokes shifts in various solvents, and the dependences of Stokes shift on solvent polarizability are consistent with solvatochromic behavior. With the ability to tune push-pull properties via the 2,7-substituent, these disubstituted sila- and germafluorenes have excellent potential as biological probes.

Push-pull dyes exhibit intramolecular charge transfer behavior, which due to changes in dipole moment upon excitation, is the origin of their sensitivity to environment. Such compounds are of interest as probes for bioimaging and as biosensors to monitor cellular dynamics and molecular interactions. Desirable biological probes absorb in the visible region, have high extinction coefficients, high quantum yield and excellent photostability. Fluorophores with scaffolding that can be used to tune and optimize solvatochromic behavior are of particular interest. Here we investigate the environmental sensitivity of a small library of highly fluorescent 2,7-disubstituted sila- and germafluorenes. Density functional theory (DFT) calculations show that charge transfer occurs from the alkyne core out to the 2,7-substitutents and 3,6-methoxy substituents, the hallmark of push-pull behavior. They exhibit a HOMO-LUMO energy gap of about 3 eV with desirable dipole moments ranging from 2-3.25 D. These compounds exhibit desirable Stokes shifts in various solvents, with absorption wavelength maxima varying up to 14 nm in polar solvents and emission wavelength maxima up to 36 nm in polar solvents compared to nonpolar solvents. Interestingly, the dependence of Stokes shift on solvent polarizability are consistent with solvatochromic behavior. With the ability to tune push-pull properties via the 2,7-substituent, these disubstituted sila- and germafluorenes have excellent potential as biological probes.