2 research outputs found
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 (Cu<sup>2+</sup>, Zn<sup>2+</sup>, and Ag<sup>+</sup>) to <b>P</b>, a gradual quenching
effect of the monomer emission is observed and found to be more pronounced
with Cu<sup>2+</sup>. 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<sup>+</sup>, Na<sup>+</sup>, K<sup>+</sup>, Mg<sup>2+</sup>, Ca<sup>2+</sup>, Ni<sup>2+</sup>, Cu<sup>2+</sup>, Zn<sup>2+</sup>, Cd<sup>2+</sup>, Hg<sup>2+</sup>, Pb<sup>2+</sup>, and Cr<sup>3+</sup> was studied by spectrophotometric and spectrofluorimetric
titrations. In the presence of Zn<sup>2+</sup>, 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 Cu<sup>2+</sup> and
Ag<sup>+</sup>, and in poly(methyl methacrylate) doped films with
promising results for Zn<sup>2+</sup> detection