Pyrene Anion Radical Research Articles

Enhanced luminescence of Au22(SG)18 nanoclusters via rational surface engineering.

We report design strategies for the preparation of highly luminescent Au22(SG)18 clusters, where SG is glutathione, by the functionalization of the cluster shell. In these strategies, the cluster shell was covalently modified with small aromatic molecules and pyrene chromophores that led to a 5-fold PL enhancement by rigidifying the shell-gold. Highly luminescent water-soluble gold clusters with a PL quantum yield of 30% were obtained at room temperature. To further enhance the luminescence, the pyrene chromophores in the functionalized Au22 clusters were photoexcited at 350 nm to induce energy transfer from pyrene to the Au22 cluster. Steady-state and time-resolved PL measurements have shown evidence of enhanced rigidity with increased PL lifetimes for the functionalized Au22 clusters. However, the energy transfer efficiency was found to be only 14% because of the competing electron transfer deactivation pathway as evidenced by the formation of the pyrene anion radical revealed in the ultrafast transient absorption measurements. To suppress the electron transfer pathway, the pyrene functionalized Au22 clusters were ion-paired with tetraoctylammonium (TOA) cations that could break the electron transfer pathway, leading to a dramatic 37-fold increase in PL brightness with the resonance energy transfer efficiency of ca. 80%. This work presents effective design strategies for the preparation of highly luminescent gold clusters by the combination of rigidifying effect and energy transfer sensitization.

Photoinduced charge separation in pyrenedicarboxamide-linked DNA hairpins

The synthesis and photophysical properties of the dihydroxypropylamide derivative of pyrene-1,6-dicaboxamide, its aniline dyad, and DNA conjugates are reported. The dicarboxamide serves as a hairpin linker for bis(oligonucleotide) conjugates having short base pair stems. The dihydroxypropyl derivative has a large fluorescence quantum yield and long singlet decay time, as determined by fluorescence and time-resolved broad band pump-probe spectroscopy. The aniline dyad undergoes exergonic charge separation with formation of a radical ion pair which decays via charge recombination. The highly characteristic transient absorption spectrum of the pyrene anion radical is used to monitor the dynamics of its formation and decay. The dicarboxamide-linked hairpin conjugates undergo charge separation with adjacent guanine and adenine bases. Charge separation with guanine is accompanied by efficient pyrene fluorescence quenching. In contrast, reversible charge separation with adenine results in multiple exponential fluorescence decay. The energetics and dynamics of charge separation are compared with those of other arenedicarboxamide DNA hairpin linkers.

Study of photo-induced electron transfer in pyrene-(CH 2) n- N, N′-dimethylaniline system by molecular dynamic simulation

The dynamic behavior of pyrene-(CH 2) n - N, N′-dimethylaniline (PnD; n = 1–3) in acetonitrile and cyclohexane was investigated with molecular dynamic simulation (MD). Then, changes in distance ( R) between pyrene and N, N-dimethylaniline moieties with time were obtained at time intervals of 1 ps for P3D, 0.1 ps for P2D and 0.02 ps for P1D. Photo-induced electron transfer (ET) rates were evaluated with Kakitani, Yoshimori and Mataga theory (KYM theory) with R at each time. The observed fluorescence intensities with lifetimes, 11 ps for P3D, 6.1 ps for P2D and 1.7 ps for P1D were obtained from observed rise times of transient absorbance of pyrene anion radicals in PnD in acetonitrile. Parameters contained in KYM theory, frequency factor ( ν 0), coefficient for criterion of adiabatic and non-adiabatic processes ( β), critical distance between adiabatic and non-adiabatic processes ( R 0) and standard free energy change (Δ G 0) were determined by a non-linear least squares method, so as to fit the calculated fluorescence intensities obtained with the observed fluorescence intensities. The calculated intensities were in good agreement with the observed ones. The values of best-fit parameters, ν 0, β, R 0, and Δ G 0 were 82.04 ps −1, 5.56 nm −1, 0.568 nm and −2.12 eV, respectively, in P3D, 82.05 ps −1, 5.56 nm −1, 0.569 nm and −2.12 eV, respectively, for P2D, and 93.19 ps −1, 5.58 nm −1, 0.698 nm and −2.08 eV, respectively, for P1D. In all systems, the ET processes were non-adiabatic. The dependence of ET rate on R were calculated with these parameters, which suggests that ET rate also exhibits a “bell shape”, such as the one obtained in the variation of Δ G 0. Therefore, ET rate may decrease with R less than 0.55 nm for all PnD (n = 1–3) systems.

Formation of π-excimer or π-exciplex in electrogenerated chemiluminescence involving perylene molecule revealed using a dual-electrolysis stopped-flow method

Electrogenerated chemiluminescence (ECL) reactions involving the perylene cation radical (PE + ) and perylene anion radical (PE − ) in acetonitrile have been observed using a dual-electrolysis stopped-flow method. In this method, ECL emission from the systems composed of different kinds of ion radicals can be easily observed by mixing both the electrolyzed solutions directly. Therefore, the ECL spectra were observed systematically in the reactions of PE + and PE − with different ion radicals. Consequently, emission definitely from the singlet state of PE was observed in the reactions between PE + and the 9,10-diphenylanthracene anion radical (DPA − ), PE − and DPA + , and PE − and the thianthrene cation radical (TH + ). In contrast, emission at long wavelength was obtained in the reaction between PE + and the pyrene anion radical (PY − ) as well as the reaction between PE + and PE − . From this result, for the molecular interactions involving PE and PY, the presence of the π complexing interaction to form the π-excimer and the π-exciplex was strongly suggested in the ECL-emitting reactions. The present approach was thus found to be effective to reveal the molecular aspects of the excited states formed in solution.

Pulse‐Electrolysis Stopped‐Flow Method for Electrogenerated Chemiluminescence in Energy Sufficient Systems

New methodology for the measurement of electrogenerated chemiluminescence (ECL) has been developed by using a pulse‐electrolysis stopped‐flow system. Using this method, the ECL from both energy sufficient and energy deficient chemical systems composed of different kinds of radical ions can be observed. In the reaction between the thianthrene cation radical and the pyrene anion radical, it was found that the emission spectra changed with the addition of the precursors, reflecting both complex electron and energy transfer processes in solution. In addition, the emitted spectrum was found to strongly depend on other molecules present when three species were mixed.

Diffuse reflectance laser photolytic studies of pyrene included in zeolites Formation of pyrene anion radicals via excited-state electron transfer between guest molecules

The formation of pyrene radical anions was observed on photo-excitation of pyrene as a result of electron transfer between pyrene molecules in the excited state and those in the ground state. This conclusion is based on the observation of concentration-dependent quenching of pyrene monomer fluorescence accompanied by a concomitant rise in the transient absorption bands of pyrene radical cation and pyrene radical anion. The present observation is significantly different in mechanism from a previous investigation in which the radical anion was found to be produced by the photo-electron transfer from host alkali metal-exchanged zeolites to excited pyrene.

Photophysical Properties of Pyrene in Zeolites: A DirectTime-Resolved Diffuse Reflectance Study of Pyrene Anion Radicals in Zeolites X and Y

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPhotophysical Properties of Pyrene in Zeolites: A DirectTime-Resolved Diffuse Reflectance Study of Pyrene Anion Radicals in Zeolites X and YXinsheng Liu, Kai-Kong Iu, and J. Kerry ThomasCite this: J. Phys. Chem. 1994, 98, 32, 7877–7884Publication Date (Print):August 1, 1994Publication History Published online1 May 2002Published inissue 1 August 1994https://doi.org/10.1021/j100083a022RIGHTS & PERMISSIONSArticle Views120Altmetric-Citations41LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (815 KB) Get e-Alerts

Photophysical properties of pyrene in zeolites. Observation of pyrene anion radicals in zeolites X and Y

Formation of pyrene anion radicals in the supercages of zeolites X and Y on photoexcitation is observed by using direct time-resolved diffuse reflectance spectroscopy, and the pyrene anion radical is found to co-exist with the pyrene cation radical.

PHOTOPHYSICS STUDIES OF ORGANIC COMPOUNDS——NANOSECOND LASER PHOTOLYSIS AND TRANSIENT ABSORPTION SPECTRA STUDIES OF PYRENE-AROMATIC AMINES

Nanosecond time-resolved transient absorption spectra of pyrene-triphenylamine, pyrenediphenylamine, pyrene-N, N-dibenzylaniline systems in various solvents have been investigated. In nonpolar solvent, pyrene-triphenylamine exciplex and pyrene-N, N-dibenzylaniline exciplex were observed directly. In acetonitrile, the pyrene anion radical, triphenylamine and diphenylamine cation radicals were detected. On the basis of the present experimental facts, the mechanism of fluorescence quenching processes of pyrene in polar and nonpolar solvents has been established.