Solutions of compound 1 exhibit dramatic, characteristic color changes in response to sugar analytes. Structurally related saccharides including glucose phosphates and amino and carboxylic acid sugars can be readily distinguished by visual inspection. These findings should promote the design of unique color sensory materials based on readily available, functional macrocyclic hosts.

A series of structurally similar fluorescent probes (1-4), synthesized from rhodamine B, were designed to optically measure pH. Each probe had a unique "off-on" response as the solution went from basic to acidic. Probes 1-3 exhibited a spiro-cyclic quenching of the pyronin B fluorophore, whereas probe 4 is quenched by PET from the amine moiety.A chemical sensor capable of measuring pH by optical methods has important implications in analytical and biological chemistry. Fluorescence based probes have demonstrated a superior ability in the detection of various analytes with high sensitivity and low detection limits. In cellular biology, the pH of specific and localized areas of the cell can be an important indication of cellular events.1 Such information could potentially be useful in the diagnosis of specific diseases. For example, colorectal cancer,2 breast cancer2b , 3, cystic fibrosis,4 and neurodegenerative disorders5 have all been linked to abnormal pH regulation, resulting in localized pH values of 4.5-6.0 that are referred to as the acidic window. Currently, a large number of fluorescence based pH sensors have been reported in the literature and are commercially available.6 However, many of these probes lack sensitivity or are simply non-responsive in the so-called "acidic window". Therefore, it would be of great benefit to aid in the diagnosis of these diseases by developing new and more sensitive probes for the measurement of pH.Many fluorescent probes operate in an "off-on" fashion, where in the "off" state the fluorescence is quenched, while the "on" state the fluorophore is fully fluorescent with a high quantum yield. Among the many fluorophores that potentially could be used as pH sensors, pyronin B has particular advantages in biological imaging because of its high quantum yield (Φ= 0.35), longer excitation and emission wavelength (550-600 nm), spectral insensitivity to solvent polarity, pH, and a high tolerance to photobleaching.7 With these criteria in mind, we set out to design a mode of regulating the fluorescence of this fluorophore by synthesizing various benzylamine derivatives at the 9-position, which have Correspondence to: Daniel J. Dyer, ddyer@chem.siu.edu. Supporting Information Available: Detailed synthetic procedures and spectra. This material is available free of charge via the Internet at http://pubs.acs.org. NIH Public Access Author ManuscriptOrg Lett. Author manuscript; available in PMC 2011 July 16. Starting with commercially available rhodamine B, we synthesized various benzylamine structures; (see supporting information for synthesis details), where the amine moiety is primary, secondary, and tertiary ( Figure 1). The rhodamine-based literature is rife with fluorescent probes that are regulated by a spirocyclic structure. These spirocyclic compounds lack absorbance and fluorescence, in visible spectrum, when engaged in the spirocyclic form but will open upon binding to specific analytes to restore the fluorophore and fluorescence intensity of that compound. Typically, th...

We report the synthesis and characterization of a fluorescent probe (Hypo-SiF) designed for the detection of hypochlorous acid (HOCl) using a silicon analogue of fluorescein (SiF). The probe is regulated in an "off-on" fashion by a highly selective thioether spirocyclic nonfluorescent structure that opens to form a mixture of fluorescent products in the presence of HOCl. Over a range of pH values, the probe reacts with a stoichiometric amount of HOCl, resulting in a mixture of two pH-dependent fluorescent species, a SiF disulfide product and a SiF sulfonate product. The unique colorimetric properties of the individual SiF fluorophores were utilized to perform simultaneous detection of HOCl and pH. When an excess of HOCl is present, the SiF fluorophores become chlorinated, via an intermediate halohydrin, resulting in a more pH independent and red-shifted fluorophore.

We report here a novel system where the rate of energy transfer is based on changes in the spectral overlap between the emission of the donor and the absorption of the acceptor (J) as well as changes in the quantum yield of the acceptor. We use the fluorophore dansyl as the donor and polydiacetylene (PDA) as the acceptor to demonstrate the modulation of FRET through conformationally induced changes in the PDA absorption spectrum following thermal treatment that converts the PDA backbone of the liposome from the blue form to the red form. Energy transfer was found to be significantly more efficient from dansyl to the red-form PDA. These findings support the basis of a new sensing platform that utilizes J-modulated FRET as an actuating mechanism.

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