Mise en place de l'expérience d'absorption transitoire femtoseconde et son application sur des dérivés du pérylène diimide

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Charge separation by photoexcitation in semicrystalline polymeric semiconductors: An intrinsic or extrinsic mechanism?

We probe charge photogeneration and subsequent recombination dynamics in neat regioregular poly(3-hexylthiophene) films over six decades in time by means of time-resolved photoluminescence spectroscopy. Exciton dissociation at 10K occurs extrinsically at interfaces between molecularly ordered and disordered domains. Polaron pairs thus produced recombine by tunnelling with distributed rates governed by the distribution of electron-hole radii. Quantum-chemical calculations suggest that hot-exciton dissociation at such interfaces results from a high charge-transfer character.Comment: 10 pages, 3 figure

Photophysical and Optical Properties of Semiconducting Polymer Nanoparticles Prepared from Hyaluronic Acid and Polysorbate 80

Copyright © 2019 American Chemical Society. A nanoprecipitation procedure was utilized to prepare novel diketopyrrolopyrrole-based semiconducting polymer nanoparticles (SPNs) with hyaluronic acid (HA) and polysorbate 80. The nanoprecipitation led to the formation of spherical nanoparticles with average diameters ranging from 100 to 200 nm, and a careful control over the structure of the parent conjugated polymers was performed to probe the influence of π-conjugation on the final photophysical and thermal stability of the resulting SPNs. Upon generation of a series of novel SPNs, the optical and photophysical properties of the new nanomaterials were probed in solution using various techniques including transmission electron microscopy, dynamic light scattering, small-angle neutron scattering, transient absorption, and UV-vis spectroscopy. A careful comparison was performed between the different SPNs to evaluate their excited-state dynamics and photophysical properties, both before and after nanoprecipitation. Interestingly, although soluble in organic solution, the nanoparticles were found to exhibit aggregative behavior, resulting in SPNs that exhibit excited-state behaviors that are very similar to aggregated polymer solutions. Based on these findings, the formation of HA- and polysorbate 80-based nanoparticles does not influence the photophysical properties of the conjugated polymers, thus opening new opportunities for the design of bioimaging agents and nanomaterials for health-related applications

Azophenine as Central Core for Efficient Light Harvesting Devices

The notoriously non-luminescent uncycled azophenine (Q) was harnessed with Bodipy and zinc(II)porphyrin antennas to probe its fluorescence properties, its ability to act as a singlet excited state energy acceptor and to mediate the transfer. Two near-IR emissions are depicted from time-resolved fluorescence spectroscopy, which are most likely due to the presence of tautomers of very similar calculated total energies (350cm(-1); DFT; B3LYP). The rates for energy transfer, k(ET)(S-1), for (1)Bodipy*Q are in the order of 10(10)-10(11)s(-1) and are surprisingly fast when considering the low absorptivity properties of the lowest energy charge transfer excited state of azophenine. The rational is provided by the calculated frontier molecular orbitals (MOs) which show atomic contributions in the C6H4CCC6H4 arms, thus favoring the double electron exchange mechanism. In the mixed-antenna Bodipy-porphyrin star molecule, the rate for (1)Bodipy*porphyrin has also been evaluated (approximate to 16x10(10)s(-1)) and is among the fastest rates reported for Bodipy-zinc(II)porphyrin pairs. This astonishing result is again explained from the atomic contributions of the C6H4CCC6H4 and CCC6H4 arms thus favouring the Dexter process. Here, for the first time, this process is found to be sensitively temperature-dependent. The azophenine turns out to be excellent for electronic communication

What does it take to induce equilibrium in bidirectional energy transfers?

Two dyads built with a co-facial slipped bis(zinc( ii )porphyrin), a free base and a bridge, [Zn 2 ]–bridge–[Fb] (bridge = C 6 H 4 CC, 1 and C 6 H 4 CCC 6 H 4 , 2), exhibit S 1 energy equilibrium [Zn 2 ]* ↔ [Fb]* at 298 K, an extremely rare situation, which depends on the degree of MO coupling between the units. At 77 K, 2 becomes bi-directional due to the two large C 6 H 4 –[Zn 2 ] and C 6 H 4 –[Fb] dihedral angles

Is pi-Stacking Prone To Accelerate Singlet-Singlet Energy Transfers?

pi-Stacking is the most common structural feature that dictates the optical and electronic properties of chromophores in the solid state. Herein, a unidirectional singlet-singlet energy-transfer dyad has been designed to test the effect of pi-stacking of zinc(II) porphyrin, [Zn-2], as a slipped dimer acceptor using a BODIPY unit, [bod], as the donor, bridged by the linker C6H4C equivalent to CC6H4. The rate of singlet energy transfer, k(ET)(S-1), at 298 K (k(ET)(S-1) = 4.5 X 10(10) s(-1)) extracted through the change in fluorescence lifetime, tau(F), of [bod] in the presence (27.1 ps) and the absence of [Zn-2] (4.61 ns) from Streak camera measurements, and the rise time of the acceptor signal in femtosecond transient absorption spectra (22.0 ps), is faster than most literature cases where no pi-stacking effect exists (i.e., monoporphyrin units). At 77 K, the tau(F), of [bod] increases to 45.3 ps, indicating that k(ET)(S-1) decreases by 2-fold (2.2 X 10(10) s(-1)), a value similar to most values reported in the literature, thus suggesting that the higher value at 298 K is thermally promoted at a higher temperature

Are the orientation and bond strength of the RCO2-center dot center dot center dot M link key factors for ultrafast electron transfers?

The photo-induced electron transfers in the "straight up" ionic assemblies [Pd-3(2+)]center dot center dot center dot MCP and [Pd-3(2+)]center dot center dot center dot DCP center dot center dot center dot[Pd-3(2+)] ([Pd-3(2+)]* -> MCP or DCP) are ultrafast (<85 fs) indicating that it is not necessary to have a strong coordination bond or a bent geometry to obtain fast electron injection in porphyrin-containing DSSCs

Unusual triplet–triplet annihilation in a 3D copper( i ) chloride coordination polymer

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Platinum Complexes of N,N',N '',N'''-Diboronazophenines

Azophenine, (alpha-C6H5NH)(2)(C6H-N=C6H2=N-C6H6), well known to be non-emissive, was rigidified by replacing two amine protons by two difluoroboranes (BF2+) and further functionalized at the pars-positions of the phenyl groups by luminescent trans-ArC C-Pt(PR3)(2)-C C ([Pt]) arms [Ar = C6H4 (R = Et), hexa(n-hexyl)-truxene) (Tru; R = Bu)]. Two effects are reported. First, the linking of these [Pt] arms with the central azophenine (C6H4-N=C6H2(NH)(2)=N-C6H4; Q) generates very low energy charge-transfer (CT) singlet and triplet excited states ((3,1)([Pt]-to-Q)*) with absorption bands extending all the way to 800 nm. Second, the rigidification of azophenine by the incorporation of BF2+ units renders the low-lying CT singlet state clearly emissive at 298 and 77 K in the near-IR region. DFT computations place the triplet emission in the 1200-1400 nm range, but no phosphorescence was detected. The photophysical properties are investigated, and circumstantial evidence for slow triplet energy transfers, (3)Tru* -> Q is provided

Increasing the lifetimes of charge separated states in porphyrin-fullerene polyads

Two linear polyads were designed using zinc(II) porphyrin, [ZnP], and N-methyl-2-phenyl-3,4-fulleropyrrolidine (C-60) where C-60 is dangling either at the terminal position of [ZnP]-C6H4-R-C6H4-[ZnP]-C-60 (1) or at the central position of [ZnP]-C6H4-R-C6H4-[ZnP(C-60)]-C6H4-R-C6H4-[ZnP] (2) in order to test whether the fact of having one or two side electron donors influences the rate of electron transfer, k(et). These polyads were studied using cyclic voltammograms, DFT computations, steady state and timeresolved fluorescence spectroscopy, and femtosecond transient absorption spectroscopy (fs-TAS). Photo-induced electron transfer confirmed by the detection of the charge separated state [ZnP center dot+]/C-60(center dot-) from fs-TAS occurs with rates (k(et)) of 3-4 x 10(10) s(-1) whereas the charge recombinations (CRs) are found to produce the [ZnP] ground state via two pathways (central [(ZnP center dot+)-Zn-1]/C-60(center dot-) (ps) and terminal central [ZnP center dot+]/C-60(center dot-) (ns) producing [(ZnP)-Zn-1] (ground state) and [(ZnP)-Zn-3*]). The formation of the T1 species is more predominant for 2