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

• Published in: Inorganic chemistry 2013-01, Vol.52 (1), p.121-129
• Main Authors: Fernández-Lodeiro, Javier, Núñez, Cristina, de Castro, Catherine S, Bértolo, Emilia, Seixas de Melo, J. Sérgio, Capelo, José Luis, Lodeiro, Carlos
• Format: Article
• Language: English
• Subjects: Dioxanes - chemistry; Fluorescent Dyes - chemical synthesis; Fluorescent Dyes - chemistry; Molecular Structure; Pyrenes - chemistry; Spectrometry, Fluorescence; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Spectrophotometry, Ultraviolet; Time Factors
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic301365y

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 (Cu2+, Zn2+, and Ag+) to P, a gradual quenching effect of the monomer emission is observed and found to be more pronounced with Cu2+. 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.