Unprecedented regioselective post-functionalization of racemic and enantiopure cationic diaza 4helicenes is afforded. The peripheral auxochrome substituents allow a general tuning of the ...electrochemical, photophysical and chiroptical properties of the helical dyes (26 examples). For instance, electronic absorption and circular dichroism are modulated from the orange to near-infrared spectral range (575-750 nm), fluorescence quantum efficiency is enhanced up to 0.55 (631 nm) and circularly polarized luminescence is recorded in the red (|
| ∼ 10
).
Disentangling overlapping spectral signatures with time-dependent shape is performed using additional information contained in ultrafast transient absorption data, without applying any assumption on ...the underlying kinetics.
SiPM time resolution: From single photon to saturation Gundacker, S.; Auffray, E.; Di Vara, N. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2013, Letnik:
718
Journal Article
Recenzirano
The time resolution of photon detection systems is important for a wide range of applications in physics and chemistry. It impacts the quality of time-resolved spectroscopy of ultrafast processes and ...has a direct influence on the best achievable time resolution of time-of-flight detectors in high-energy and medical physics. For the characterization of photon detectors, it is important to measure their exact timing properties in dependence of the photon flux and the operational parameters of the photodetector and its accompanying electronics. We report on the timing of silicon photomultipliers (SiPM) as a function of their bias voltage, electronics threshold settings and the number of impinging photons. We used ultrashort laser pulses at 400nm wavelength with pulse duration below 200fs. We focus our studies on different types of SiPMs (Hamamatsu MPPC S10931-025P, S10931-050P and S10931-100P) with different SPAD sizes (25μm, 50μm and 100μm) coupled to the ultrafast discriminator amplifier NINO. For the SiPMs, an optimum in the time resolution regarding bias and threshold settings can be reached. For the 50μm type, we achieve a single photon time resolution of 80ps sigma, and for saturating photon fluxes better than 10ps sigma.
Several controversial questions in the field of bimolecular photoinduced electron transfer reactions in polar solvents are first briefly reviewed. Results obtained in our group using ultrafast ...spectroscopy and giving a new insight into these problems will then be described. They concern the driving force dependence of the charge separation distance, the formation of the reaction product in an electronic excited state, the absence of normal region for weakly exergonic charge recombination processes and the excitation wavelength dependence of the CR dynamics of donor–acceptor complexes.
A novel N-substituted 4-methoxy-1,8-naphthalimide (NAFTA 8) especially designed for fluorescent labeling of gold nanoparticles has been synthesized. NAFTA 8 bears a long methylene chain at the imide ...N atom and has a terminal SH group, which enables its chemical binding to gold nanostructures. The longest wavelength absorption maximum of NAFTA 8 in chloroform is at 370
nm, the fluorescent maximum is at 430
nm and the fluorescent quantum yield is 0.95. The newly synthesized fluorophore is applied for functionalization of gold nanoparticles with diameter 1.5
±
0.5
nm prepared through chemical reduction. The obtained Monolayer Protected Clusters are characterized by elemental analysis, TEM, XPS, FT-IR, absorption and fluorescence spectroscopy. The performed investigations provide evidence for the formation of chemical bond between the thiol ligand and the gold surface. They also show that the obtained metal/dielectric 3D structures are highly fluorescent.
The dynamics of charge recombination in a photoexcited donor-acceptor complex comprising 1,2,4-trimethoxybenzene (electron donor) and tetracyanoethylene (electron acceptor) in several polar solvents ...(acetonitrile, valeronitrile, and octanonitrile) was studied in terms of the stochastic approach. The Gibbs energy of charge recombination and the reorganization energies of the medium and quantum and vibrational degrees of freedom were found by fitting the stationary absorption spectrum. The electronic couplings were determined by analyzing the time dependences of the population of the ionic state in acetonitrile. A comparison of the numerical simulation results with the experimental data showed that the nonstationary model under consideration quantitatively described the dynamics of charge recombination and its dependence on the carrier frequency of excitation pulses and the relaxation properties of solvents.
The excitation of a charge transfer band by a laser pulse of finite duration and the ensuing charge recombination are calculated in the framework of the perturbation theory. The influence of the ...spectral characteristics of the laser pulse on the charge recombination dynamics is investigated for models including several nuclear modes that differ greatly in their timescales. It is shown that, in the area of applicability of the perturbation theory, the variation of the pulse carrier frequency inside the absorption band can significantly change the effective charge recombination rate constant.
The large amplitude motion connected with CT formation in DMABN is controlled by the activation entropy (the Arrhenius prefactor). A possible explanation is a conical intersection necessitating a ...two-dimensional description of the reaction.
The kinetics of the dual fluorescence of several derivatives of dimethylaminobenzonitrile (DMABN) has been compared using fs-fluorescence upconversion experiments. Variation of the size and twist angle of the donor (dialkylamino group) suggest a large amplitude solvent-viscosity controlled diffusional twisting motion towards larger twist angles as the rate limiting step.
Large rate differences were observed for an ester group as acceptor. Temperature dependent studies indicate that these differences are not connected with different activation barriers but with changes in the Arrhenius preexponential factor. It is argued that conical intersections along the reaction path can bring about these entropy changes.
Previously, we have shown that the use of a cyclopeptidic carrier could be of great interest for the design of fully characterized prodrugs for further use in photodynamic therapy. In order to ...further optimize the design, we decided to modify the highly quenched conjugate uPA-cPPP
by co-loading a long-distance fluorescence quencher. For this purpose we tethered two black hole quenchers (BHQ3) together with two pheophorbide A moities onto the same PEGylated backbone and assessed the modified photophysical properties. In addition, to prove the reliability of our concept, we designed two analogues, uPA-cPPQ
and CathB-cPPQ
, by using two different peptidic linkers as substrates for uPA and cathepsin B, respectively. These two conjugates proved to be much more water-soluble than their analogues bearing only Phas. These conjugates are not only highly quenched in their native state with regard to their fluorescence emission (up to 850 ± 287 times less fluorescent for CathB-cPPQ
as compared to the unquenched monosubstituted reference uPA-cPPP
), but also prevent singlet oxygen production (with a total quenching of the emission when the quenchers are co-loaded with photosensitizers) when the photosentistizers are excited. After proteolytic activation, these conjugates recover their photophysical properties in the same way as occurred for uPA-cPPP
, with up to a 120-fold increase in fluorescence emission for uPA-cPPQ
after two hours of incubation with uPA.
![Functionalized cationic [4]...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/2041-6520_2041-6539/small "Functionalized cationic [4]helicenes with unique tuning of absorption, fluorescence and chiroptical properties up to the far-red range")
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