State Dependent Photochemical and Photophysical Behavior of Dithiolate Ester and Trithiocarbonate RAFT Polymerization Agents.

2020 ◽  
Author(s):  
Daniel Falvey ◽  
Matthew Thum ◽  
Steven Wolf
Keyword(s):  
Electron Transfer ◽  
Transient Absorption ◽  
Raft Polymerization ◽  
Photophysical Properties ◽  
Energy Levels ◽  
Transient Absorption Spectroscopy ◽  
Quantum Yields ◽  
Peak Reduction ◽  
Initiation Mechanism ◽  
Reduction Potentials

The rise in popularity of photochemically initiated RAFT polymerization (photoRAFT) along with the broad spectrum of proposed, and possible, initiation mechanisms results in the need for careful characterization of the photophysical properties of some common RAFT agents. Direct irradiation of the RAFT agent as a means to generate radicals, also known as the photoiniferter mechanism, is one commonly proposed mechanism. The current study shows that the dithioesters and trithiocarbonates have lowest singlet, and triplet excited state energy levels that are close to, or lower then C-S bond dissociation energies. Excitation of these agents into their S<sub>1</sub> band results in negligible radical production, while excitation into S<sub>2</sub> or higher results in the decomposition of dithioesters and trithiocarbonates resulting in radical formation, but with low quantum yields. Likewise, there is significant literature precedence for an electron transfer initiation mechanism, PET-RAFT. It is shown that the dithioesters and trithiocarbonates all show peak reduction potentials at ca. -1.0 V (vs. SCE). However, transient absorption spectroscopy studies of the electron transfer from a mediator shows that theses reactions occur rapidly only when the mediator potential is more negative than -1.2 V (vs. SCE).

State Dependent Photochemical and Photophysical Behavior of Dithiolate Ester and Trithiocarbonate RAFT Polymerization Agents.

2020 ◽  
Author(s):  
Daniel Falvey ◽  
Matthew Thum ◽  
Steven Wolf
Keyword(s):  
Electron Transfer ◽  
Transient Absorption ◽  
Raft Polymerization ◽  
Photophysical Properties ◽  
Energy Levels ◽  
Transient Absorption Spectroscopy ◽  
Quantum Yields ◽  
Peak Reduction ◽  
Initiation Mechanism ◽  
Reduction Potentials

The rise in popularity of photochemically initiated RAFT polymerization (photoRAFT) along with the broad spectrum of proposed, and possible, initiation mechanisms results in the need for careful characterization of the photophysical properties of some common RAFT agents. Direct irradiation of the RAFT agent as a means to generate radicals, also known as the photoiniferter mechanism, is one commonly proposed mechanism. The current study shows that the dithioesters and trithiocarbonates have lowest singlet, and triplet excited state energy levels that are close to, or lower then C-S bond dissociation energies. Excitation of these agents into their S<sub>1</sub> band results in negligible radical production, while excitation into S<sub>2</sub> or higher results in the decomposition of dithioesters and trithiocarbonates resulting in radical formation, but with low quantum yields. Likewise, there is significant literature precedence for an electron transfer initiation mechanism, PET-RAFT. It is shown that the dithioesters and trithiocarbonates all show peak reduction potentials at ca. -1.0 V (vs. SCE). However, transient absorption spectroscopy studies of the electron transfer from a mediator shows that theses reactions occur rapidly only when the mediator potential is more negative than -1.2 V (vs. SCE).

scholarly journals Investigation of the Photophysical Properties of a Eu3+ Coordination Polymer Bearing an α-Nitrile Substituted β-Diketonate Ligand via Emission and Ultrafast Transient Absorption Spectroscopy

2015 ◽  
Vol 68 (9) ◽  
pp. 1392 ◽  
Author(s):  
Brodie L. Reid ◽  
Evan G. Moore ◽  
Brian W. Skelton ◽  
Mark I. Ogden ◽  
Massimiliano Massi
Keyword(s):  
Coordination Polymer ◽  
Absorption Spectroscopy ◽  
Transient Absorption ◽  
Photophysical Properties ◽  
Transient Absorption Spectroscopy ◽  
Quantum Yields ◽  
Metal Centre ◽  
Antenna Effect ◽  
One Dimensional ◽  
Polymer Bearing

Reaction of the β-diketone ligand, 2-cyano-1,3-phenyl-1,3-propandione (LH), with hydrated EuCl3 in the presence of 1,10-phenanthroline (Phen), results in the crystallisation of a one-dimensional Eu3+ coordination polymer of formulation [Eu(Phen)(L)3]∞, formed by coordination of the nitrile group of an O,O′-bound ligand to a neighbouring metal centre. An investigation of the metal-centred emission of the polymer, both in the solid state and solution, revealed red emission characterised by relatively long-lived excited state lifetimes and high intrinsic quantum yields. However, analysis of the overall quantum yield and sensitisation efficiency reveals that ultrafast processes in the ligand potentially inhibit Eu3+ sensitisation. Further investigations into these processes using transient absorption spectroscopy suggest that substitution at the α-C position may significantly decrease sensitisation via the antenna effect.

scholarly journals Photoinduced electron transfer processes of single-wall carbon nanotube (SWCNT)–based hybrids

Nanophotonics ◽  
2020 ◽  
Vol 9 (16) ◽  
pp. 4689-4701
Author(s):  
Lili Du ◽  
Wenjuan Xiong ◽  
Wai Kin Chan ◽  
David Lee Phillips
Keyword(s):  
Electron Transfer ◽  
Transient Absorption ◽  
Electronic Materials ◽  
Photophysical Properties ◽  
Functional Materials ◽  
Single Wall Carbon Nanotubes ◽  
Spectroscopic Techniques ◽  
Time Resolved ◽  
Single Wall Carbon ◽  
Electron Transfer Processes

AbstractIn this review, noncovalent functionalization of single-wall carbon nanotubes (SWCNTs) is briefly reviewed. The functional materials summarized here include metalloporphyrin derivatives, biomolecules and conjugated polymers. Notably, time-resolved spectroscopic techniques such as time-resolved fluorescence and transient absorption were employed to directly investigate the electron transfer and recombination processes between the functionalities and the SWCNTs. In addition, Raman spectroscopy is also useful to identify the interaction and the electron transfer direction between both the functionalities and the SWCNTs. An improved understanding of the mechanisms of these SWCNT-based nanohybrids in terms of their structural and photophysical properties can provide more insights into the design of new electronic materials.

scholarly journals The Temperature Dependence of Fundamental Photophysical Properties of [Eu(MeOH-d4)9]3+ Solvates and [Eu.DOTA(MeOH-d4)]- Complexes

2021 ◽  
Author(s):  
Nicolaj Kofod ◽  
Lea Gundorff Nielsen ◽  
Thomas Just Sørensen
Keyword(s):  
Transition Probabilities ◽  
Photophysical Properties ◽  
Transition Probability ◽  
Energy Levels ◽  
Emission Spectra ◽  
Lanthanide Ions ◽  
Quantum Yields ◽  
Luminescence Spectra ◽  
Absorption Cross ◽  
Apparent Lack

The trivalent lanthanide ions show optical transitions between energy levels within the 4f shell. All these transitions are formally forbidden according to the quantum mechanical selection rules used in molecular photophysics. Nevertheless, highly luminescent complexes can be achieved, and terbium(iii) and europium(iii) ions are particularly efficient emitters. This report started when an apparent lack of data in the literature led us to revisit the fundamental photophysics of europium(iii). The photophysical properties of two complexes – [Eu.DOTA(MeOH-d4)]- and [Eu(MeOH-d4)9]3+ – were investigated in deuterated methanol at five different temperatures. Absorption spectra showed decreased absorption cross sections as the temperature was increased. Luminescence spectra and time-resolved emission decay profiles showed a decrease in intensity and lifetime as a temperature was increased. Having corrected the emission spectra for the actual number of absorbed photons and differences in non-radiative pathways, the relative emission probability was revealed. These were found to increase with increasing temperature. The transition probability for luminescence was shown to increase with temperature, while the transition probability for light absorption decreased. The changes in transition probabilities were correlated to a change in the symmetry of the absorber or emitter, with an average increase in symmetry lowering absorption cross section and access to more asymmetric structures increasing the emission rate constant. Determining luminescence quantum yields and the Einstein coefficient for spontaneous emission allowed us to conclude that lowering symmetry increases both. Further, it was found that collisional self-quenching is an issue for lanthanide luminescence, when high concentrations are used. Finally, detailed analysis revealed results that show the so-called ‘Werts’ method’ for calculating radiative lifetimes and intrinsic quantum yields are based on assumption that does not hold for the two systems investigated here. We conclude that we are lacking a good theoretical description of the intraconfigurational f-f transition, and that there are still aspects of fundamental lanthanide photophysics to be explored.<br>

Photoinduced electron transfer dynamics in dye-sensitized ZnO nanowire photoanodes

2018 ◽  
Vol 32 (19) ◽  
pp. 1840049
Author(s):  
Akihiro Furube ◽  
Takahiro Arai ◽  
Masahiro Okazaki ◽  
Shinichiro Yanagiya ◽  
Liang-Yih Chen ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Transient Absorption ◽  
Low Cost ◽  
Transient Absorption Spectroscopy ◽  
Zno Nanowire ◽  
Dye Sensitized ◽  
Femtosecond Transient Absorption ◽  
State Formula ◽  
Flexible Solar Cell

A photoanode using dye-sensitized ZnO nanowire (NW) is a good candidate for low-cost, colorful, light-weight and flexible solar cell material. We have synthesized a ZnO NW anode and a ZnO nanowire–nanoparticle (NWNP) anode, in which ZnO nanoparticles (NPs) are decollated on the surface of NWs. Photo-induced electron transfer dynamics from the excited state of sensitizer dye (D149) to the conduction band of ZnO NW and ZnO NWNP was clarified using femtosecond transient absorption spectroscopy. The decay of the single excited state ([Formula: see text]) of D149 was faster in ZnO NW than that of ZnO NWNP, indicating that NW is more suitable as an efficient electron acceptor.

Transient Absorption Spectroscopy of the Electron Transfer Step in the Photochemically Activated Polymerizations of N-ethylcarbazole and 9-phenylcarbazole.

2021 ◽  
Author(s):  
Georgia Thornton ◽  
Ryan Phelps ◽  
Andrew Orr-Ewing
Keyword(s):  
Electron Transfer ◽  
Radical Cation ◽  
Absorption Spectroscopy ◽  
Electron Acceptor ◽  
Transient Absorption ◽  
Transient Absorption Spectroscopy ◽  
Transfer Step

The polymerization of photoexcited N-ethylcarbazole (N-EC) in the presence of an electron acceptor begins with an electron transfer (ET) step to generate a radical cation of N-EC (N-EC+.). Here, the...

Synthesis, characterization and photophysical properties of ferrocenyl and mixed sandwich cobaltocenyl ester linked meso-triaryl corrole dyads

2017 ◽  
Vol 21 (10) ◽  
pp. 646-657 ◽  
Author(s):  
B. Shivaprasad Achary ◽  
A. R. Ramya ◽  
Rajiv Trivedi ◽  
P. R. Bangal ◽  
L. Giribabu
Keyword(s):  
Transient Absorption ◽  
Photophysical Properties ◽  
Heavy Atom ◽  
Parent Compound ◽  
Fluorescence Emission ◽  
Soret Band ◽  
Transient Absorption Spectroscopy ◽  
Ferrocene Derivatives ◽  
Time Resolved ◽  
Design And Synthesis

We report here the design and synthesis of corrole-metallocene dyads consisting of a metallocene (either ferrocene (Dyad 1) or mixed sandwich [Formula: see text]-[C[Formula: see text]H[Formula: see text](COOH)]Co([Formula: see text]-C[Formula: see text]Ph[Formula: see text] (Dyad 2)) connected via an ester linkage at meso phenyl position. Both the dyads were characterized by [Formula: see text]H NMR, MALDI-TOF, UV-visible, fluorescence spectroscopies (steady-state, picosecond time-resolved), femtosecond transient absorption spectroscopy (fs-TA) and electrochemical methods. The absorption spectra of these dyads showed slight broadening and splitting of the Soret band that indicates a weak ground state interaction between the corrole macrocycle and metallocene part of the present donor–acceptor (D–A) system. However, in both the dyad systems, fluorescence emission of the corrole was quenched in polar solvents as compared to its parent compound 10-(4-hydroxyphenyl)-5,15-bis-(pentafluorophenyl ) corrole (Ph-Corr). The quenching was more pronounced in ferrocene derivatives than in cobaltocenyl derivatives. Transient absorption studies confirm the absence of photoinduced electron transfer from metallocene to correl for these dyad systems and the quenching of singlet state of corrole is found to enhance intersystem crossing due to heavy atom effect.

scholarly journals Effect of Some Substituents Increasing the Solubility of Zn(II) and Al(III) Phthalocyanines on Their Photophysical Properties

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
A. A. Chernonosov ◽  
E. A. Ermilov ◽  
B. Röder ◽  
L. I. Solovyova ◽  
O. S. Fedorova
Keyword(s):  
Absorption Spectra ◽  
Structural Changes ◽  
Water Solubility ◽  
Transient Absorption ◽  
Photophysical Properties ◽  
Water Soluble ◽  
Quantum Yields ◽  
Carboxyl Groups ◽  
Transient Absorption Spectra ◽  
Photochemical Properties

Water solubility of phthalocyanines (Pcs) usually increases by the introduction of charged or carboxy substituents in the peripheral positions of the macrocycle. As a result, such structural changes influence their photophysical and photochemical properties as photosensitizers. Phthalocyanines substituted with four or eight terminal carboxyl groups and having in some cases additional eight positive charges (water soluble phthalocyanines) were studied in order to evaluate the spectroscopic and photophysical effects of these side residues on the chromophore properties. The quantum yield of singlet oxygen (O12) generation, the triplet-triplet absorption, and the transient absorption spectra were measured and linked to the structure of the substituents. It was shown that charged substituents did not change the quantum yields ofO12generation but decrease its lifetimes. The introduction of the charged substituents not only increases the water solubility but also significantly changes absorption, fluorescence, and transient absorption spectra of water soluble Pcs.

scholarly journals Multiphoton Ionization of Nitrobenzene in Non-Aqueous Solutions: Characterization of the Cation and Ion-Molecule Chemistry

1991 ◽  
Vol 11 (2) ◽  
pp. 83-93 ◽  
Author(s):  
G. Siuzdak ◽  
J. J. Belbruno
Keyword(s):  
Aqueous Solutions ◽  
Absorption Spectroscopy ◽  
Ion Mobility ◽  
Transient Absorption ◽  
Multiphoton Ionization ◽  
Transient Absorption Spectroscopy ◽  
Quantum Yields ◽  
Nanosecond Pulses ◽  
Solvent Molecules

The phenoxy cation has been generated in polar and nonpolar solutions by multiphoton ionization of nitrobenzene using nanosecond pulses of 266 nm and 355 nm light. The ions have been characterized by pulsed conductivity (ion mobility) measurements and transient absorption spectroscopy. The involvement of the phenoxy ion in ion-molecule chemistry with either neutral solute or solvent molecules has also been observed and the photochemical products and quantum yields of the ion-molecule products are presented and compared with the neutral photochemistry results.

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