Steady-State and Time-Resolved Investigations on Pyrene-Based Chemosensors

Two novel fluorescent probes bearing a single (<b>P</b>) and two (a podand-like structure, <b>L</b>) pyrene units derived from 1,5-bis­(2-aminophenoxy)-3-oxopentane have been synthesized and investigated in dioxane using UV–vis absorption, and steady-state and time-resolved (in a picosecond time scale) emission spectroscopy; in the gas phase, matrix-assisted laser desorption ionization mass spectrometry was employed. In dioxane, the absorption and emission spectra of <b>P</b> present a unique band with maxima at 361 and 392 nm, which have been associated with the monomer absorption and emission bands, respectively. In dioxane, for compound <b>L</b>, an additional band with a maximum at ∼525 nm is observed; upon the addition of water, an emissive band (with maxima varying from 405 to 490 nm) appears in both <b>P</b> and <b>L</b> spectra; this is discussed in terms of the emission of a species with charge character. Upon metal addition (Cu²⁺, Zn²⁺, and Ag⁺) to <b>P</b>, a gradual quenching effect of the monomer emission is observed and found to be more pronounced with Cu²⁺. In the case of <b>L</b>, upon the addition of metal cations, the long emission band (∼550 nm) decreases and the monomer emission band increases (with an isoemissive point at ∼450 nm) and no evidence for the intermediate band (at ∼405–490 nm) now exists. Time-resolved data in dioxane/water mixtures showed that for <b>P</b> and <b>L</b> these two fit double- and triple-exponential decay laws, respectively. With <b>P</b>, this has been attributed to a two-state system, which involves the monomer and a charged species, with its emission maxima varying with the polarity of the media (here mirrored by its dielectric constant), which can potentially be addressed to an exciplex-like species, whereas with <b>L</b>, it has been attributed to a three-state system involving, in addition to these two species, an excimer. From absorption and fluorescence excitation and time-resolved data, evidence is given for the presence of intramolecular dimer formation in the ground state

Synthesis, Spectroscopy Studies, and Theoretical Calculations of New Fluorescent Probes Based on Pyrazole Containing Porphyrins for Zn(II), Cd(II), and Hg(II) Optical Detection

New pyrazole–porphyrin conjugates were successfully prepared from a reaction of β-porphyrin–chalcone derivatives with phenylhydrazine in acetic acid followed by an oxidative step. This fast and efficient synthetic approach provided the expected compounds in yields up to 82%. The sensing ability of the new porphyrin–pyrazole derivatives to detect the metal ions Ag⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Pb²⁺, and Cr³⁺ was studied by spectrophotometric and spectrofluorimetric titrations. In the presence of Zn²⁺, the conjugates exhibit changes in the emission spectra that are desired for a ratiometric-type fluoroionophoric detection probe. The studies were extended to gas phase, where the pyrazole–porphyrin conjugates show ability to sense metal ions with high selectivity toward Cu²⁺ and Ag⁺, and in poly­(methyl methacrylate) doped films with promising results for Zn²⁺ detection

Porphyrin-Oligopyridine Triads: Synthesis and Optical Properties

The synthesis of two triads with two porphyrinyl units linked by oligopyridine derivatives and a new β-functionalized porphyrin-dihydroazepine is described. One of the porphyrin-oligopyridine triads has a quinquepyridine unit connecting the porphyrins β-pyrrolic positions, while the other one has an asymmetric quaterpyridine with one of the pyridines fused to the porphyrin. All compounds have fluorescence emission quantum yields in the range of <i>meso</i>-tetraphenylporphyrin (16–22%)