Photolysis Dynamics Laser Chemistry Lab

We report a ratiometric fluorescent metal ion sensor based on the mechanism of fluorescence resonance energy transfer (FRET) between synthesized 15-crown-5-ether capped CdSe/ZnS quantum dots (QDCE) and 15-crown-5-ether attached rhodamine B (RBCE) in pH 8.3 buffer solution. Fluorescence titration with different metal ions in pH 8.3 buffer solution of the QDCE-RBCE conjugate showed a decrease and an increase in the fluorescence intensity for QDCE and RBCE moieties respectively due to FRET from QDCE to RBCE. This sensor system shows excellent selectivity towards K+ ions resulting in increasing efficiency of FRET. Energy transfer efficiency depends on the affinity between metal ions and crown ether functionalized with QDCE/RBCE. The detailed analysis of FRET was explored. This water soluble ratiometric sensor system can act as a good FRET probe for sensing applications especially in biological systems. © The Royal Society of Chemistry 2015.

Abstract The nanohybrids of noble metal (M=Ag, Au, Pd, Pt, and Ru) nanoparticle-decorated rhenium disulfide nanosheets (ReS2 NSs) were demonstrated as excellent catalysts towards the reduction of aromatic nitro compounds. The M/ReS2 nanohybrids were synthesized by facile hydrothermal method and characterization results proved that each metal nanoparticle was anchored on the ReS2 NSs. These nanohybrids exhibited superior catalytic performance towards the reduction of aromatic nitro compounds including 4-nitrophenol, 2-nitroaniline, and nitrobenzene. Interestingly, the Ru/ReS2 and Pd/ReS2 showed enhanced catalytic reduction compared to Ag/ReS2, Au/ReS2, and Pt/ReS2 and also showed significant catalytic stability due to metal nanoparticles anchored strongly on the surface of ReS2 NSs. Moreover, these M/ReS2 nanohybrids turned out to have much better catalytic performance compared to noble metal nanoparticle-based catalysts. A plausible reduction mechanism was proposed for each nitro compound. It was verified that the metal-nanoparticle-mediated hydrogen transfer was involved in the reduction of nitro compounds to amines. This report demonstrates the catalytic activities for metal nanoparticle-decorated ReS2 nanohybrids, which can serve as a paradigm to open up a future trend in the design of transition metal dichalcogenides nanohybrids as superior catalysts.

The primary elimination channel of bromine molecule in one-photon dissociation of CH2BrC(O)Br at 248 nm is investigated using cavity ring-down absorption spectroscopy. By means of spectral simulation, the ratio of nascent vibrational population in v 0, 1, and 2 levels is evaluated to be 1:(0.5 ± 0.1):(0.2 ± 0.1), corresponding to a Boltzmann vibrational temperature of 581 ± 45 K. The quantum yield of the ground state Br2 elimination reaction is determined to be 0.24 ± 0.08. With the aid of ab initio potential energy calculations, the obtained Br2 fragments are anticipated to dissociate on the electronic ground state, yielding vibrationally hot Br2 products. The temperature-dependence measurements support the proposed pathway via internal conversion. For comparison, the Br2 yields are obtained analogously from CH3CHBrC(O)Br and (CH3)2CBrC(O)Br to be 0.03 and 0.06, respectively. The trend of Br2 yields among the three compounds is consistent with the branching ratio evaluation by Rice-Ramsperger-Kassel-Marcus method. However, the latter result for each molecule is smaller by an order of magnitude than the yield findings. A non-statistical pathway so-called roaming process might be an alternative to the Br2 production, and its contribution might account for the underestimate of the branching ratio calculations. © 2012 American Institute of Physics.

Ion imaging coupled with (2 + 1) resonance-enhanced multiphoton ionization (REMPI) technique is employed to probe CO(v″ = 0) fragments at different rotational levels following photodissociation of methyl formate (HCOOCH 3) at 234 nm. When the rotational level, J″CO, is larger than 24, only a broad translational energy distribution extending beyond 70 kcal mol-1 with an average energy of about 23 kcal mol -1 appears. The dissociation process is initiated on the energetic ground state HCOOCH3 that surpasses a tight transition state along the reaction coordinate prior to breaking into CO + CH3OH. This molecular dissociation pathway accounts for the CO fragment with larger rotational energy and large translational energy. As J″CO decreases, a bimodal distribution arises with one broad component and the other sharp component carrying the average energy of only 1-2 kcal mol-1. The branching ratio of the sharp component increases with a decrease of J″CO; (7.3 ± 0.6)% is reached as the image is probed at J″CO = 10. The production of a sharp component is ascribed to a roaming mechanism that has the following features: a small total translational energy, a low rotational energy partitioning in CO, but a large internal energy in the CH3OH co-product. The internal energy deposition in the fragments shows distinct difference from those via the conventional transition state. © the Owner Societies 2011.

Atmospheric halogen chemistry has drawn much attention, because the halogen atom (X) playing a catalytic role may cause severe stratospheric ozone depletion. Atomic X elimination from X-containing hydrocarbons is recognized as the major primary dissociation process upon UV-light irradiation, whereas direct elimination of the X2 product has been seldom discussed or remained a controversial issue. This account is intended to review the detection of X2 primary products using cavity ring-down absorption spectroscopy in the photolysis at 248 nm of a variety of X-containing compounds, focusing on bromomethanes (CH2Br2, CF2Br2, CHBr2Cl, and CHBr3), dibromoethanes (1,1-C 2H4Br2 and 1,2-C2H 4Br2) and dibromoethylenes (1,1-C2H 2Br2 and 1,2-C2H2Br2), diiodomethane (CH2I2), thionyl chloride (SOCl 2), and sulfuryl chloride (SO2Cl2), along with a brief discussion on acyl bromides (BrCOCOBr and CH2BrCOBr). The optical spectra, quantum yields, and vibrational population distributions of the X2 fragments have been characterized, especially for Br2 and I2. With the aid of ab initio calculations of potential energies and rate constants, the detailed photodissociation mechanisms may be comprehended. Such studies are fundamentally important to gain insight into the dissociation dynamics and may also practically help to assess the halogen-related environmental variation. This journal is © the Partner Organisations 2014.

Palladium nanoparticles encapsulated in the carbon dots (Pd/C-dots) are demonstrated to play a role of multifunctional nanohybrid in the synergetic applications of sensor and catalysis. The photochemical method is applied to synthesize Pd/C-dots in which Pd nanoparticles (NPs) are dispersedly encapsulated by C-dots layer. The nanohybrid can function as a fluorescent sensor and reductive catalyst, due to the inherent properties of C-dots and Pd NPs, respectively. The Pd/C-dots exhibit a highly selective and sensitive detection toward the nickel (Ni2+) ion with a detection limit of 7.26 × 10−9 m. Moreover, the Ni2+ is detected in MCF-7 live cells signifying the applicability of nanohybrid as a promising sensor. On the other hand, the Pd/C-dots show an excellent catalytic performance in the reduction of 4-nitrophenol and eosin yellow. A plausible mechanism for sensing and catalysis behavior is proposed. The sensor system is designed on the basis of the fluorescence turn-on when Ni2+ interacts with functional groups of the C-dots layer. The activities of catalytic reduction are mainly governed by the Pd NPs and further enhanced when the C-dots layer is incorporated. The Pd/C-dots can serve as a new paradigm for opening a potential trend in the design of multifunctional materials to diverse applications. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim