title: Steady-state and time-resolved investigations on pyrene-based chemosensors.
abstract: Two novel fluorescent probes bearing a single (P) and two (a podand-like structure, L) 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 P 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 L, 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 P and L spectra; this is discussed in terms of the emission of a species with charge character. Upon metal addition (Cu(2+), Zn(2+), and Ag(+)) to P, a gradual quenching effect of the monomer emission is observed and found to be more pronounced with Cu(2+). In the case of L, 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 P and L these two fit double- and triple-exponential decay laws, respectively. With P, 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 L, 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.
authors.affiliation: Grupo BIOSCOPE, Departamento de Química, Facultade de Ciencias, Campus de Ourense, Universidade de Vigo, 32004 Vigo, Spain.
authors.forename: Javier
authors.initials: J
authors.lastname: Fernández-Lodeiro
authors.forename: Cristina
authors.initials: C
authors.lastname: Núñez
authors.forename: Catherine S
authors.initials: CS
authors.lastname: de Castro
authors.forename: Emilia
authors.initials: E
authors.lastname: Bértolo
authors.forename: J Sérgio
authors.initials: JS
authors.lastname: Seixas de Melo
authors.forename: José Luis
authors.initials: JL
authors.lastname: Capelo
authors.forename: Carlos
authors.initials: C
authors.lastname: Lodeiro
mesh_terms: D004146:Dioxanes / Q000737:chemistry; D005456:Fluorescent Dyes / Q000138:chemical synthesis / Q000737:chemistry*; D015394:Molecular Structure; D011721:Pyrenes / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013056:Spectrophotometry, Ultraviolet; D013997:Time Factors
chemical_list: D004146:Dioxanes; D005456:Fluorescent Dyes; D011721:Pyrenes; C030984:pyrene; C025223:1,4-dioxane