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Near-Infrared Photoelectrochemical Conversion via Photoinduced Charge Separation in Supramolecular Complexes of Anionic Phthalocyanines with Li+@C60

Two phthalocyanines possessing carboxylate groups ((TBA)4H2Pc·1 and (TBA)4H2Pc·2) form 1:2 supramolecular complexes with lithium cation-encapsulated C60 (Li(+)@C60) [H2Pc·1(4-)/(Li(+)@C60)2 and H2Pc·2(4-)/(Li(+)@C60)2] in a polar mixed solvent. From the UV-vis spectral changes, the binding constants (K) were estimated as ca. 10(12) M(-2). Upon the photoexcitation of constructed supramolecular complexes, photoinduced electron transfer occurred to form the charge-separated (CS) state. The lifetime of the CS state was determined to be 1.2 ms for H2Pc·2(4-)/(Li(+)@C60)2, which is the longest CS lifetime among the porphyrinoid/fullerene supramolecular complexes. H2Pc·1(4-)/(Li(+)@C60)2 also afforded the long-lived CS state of 1.0 ms. The spin state of the long-lived CS states was determined to be a triplet, as indicated by the EPR signal at g = 4. The reorganization energy (λ) and the electronic coupling term were determined to be λ = 1.70 eV, V = 0.15 cm(-1) from the temperature dependence of the rate constant for the charge recombination of the CS state of H2Pc·1(4-)/(Li(+)@C60)2. The energy of the CS state (0.49 eV) is much smaller than the reorganization energy, indicating that the back-electron-transfer process is located in the Marcus normal region. The small electronic coupling term results from the spin-forbidden back electron transfer due to the triplet CS state. Supramolecular complexes of anionic zinc phthalocyanines with Li(+)@C60 were also prepared and investigated. The ZnPc·4(4-)/Li(+)@C60 supramolecular nanoclusters were assembled on the optically transparent electrode (OTE) of nanostructured SnO2 (OTE/SnO2) to construct the dye-sensitized solar cell. The IPCE (incident photon-to-photocurrent efficiency) values of OTE/SnO2/(ZnPc·4(4-)/Li(+)@C60)n were much higher than the sum of the two IPCE values of the individual systems OTE/SnO2/(Li(+)@C60)n and OTE/SnO2/(ZnPc·4(4-))n, covering the near-infrared region.

Millisecond photorefractivity with novel dicyanomethylenedihydrofuran-containing polymers

New multifunctional copolymers containing carbazole units and high loads of dicyanomethylenedihydrofuran (DCDHF) were synthesized and used to prepare blends for photorefractive (PR) purposes. The materials response, which is strongly dependent on the glass-transition temperature (Tg), was thoroughly analyzed by holography, conductivity and ellipsometry measurements in order to both determine the limiting factors and optimize the performance. Materials that have a Tg around room temperature show strongly hindered chromophore orientation, which is avoided by lowering the Tg down to 6 °C, without compromising the PR effect or the material stability. A further DCDHF-containing homopolymer without carbazole was synthesized and characterized, showing an inferior PR response, which is attributed to a beneficial role for charge generation and transport of the attached carbazole in the copolymers. The new blends strongly improve the structural properties of previous DCDHF-based materials, allowing application of fields well above 100 V μm−1 and preventing beam fanning. Outstanding PR performance was achieved, with fast buildup and erasure times of a few tens of milliseconds (even at low recording intensities), large refractive index modulation (over 10−2) and two-beam coupling gain (above 350 cm−1). Such performance is among the best reported for PR materials based on multifunctional and nonlinear polymers and comparable to standard PR composites.

Water soluble fluorescent-magnetic perylenediimide-containing maghemite-nanoparticles for bimodal MRI/OI imaging.

The protein shell of apoferritin-encapsulated maghemite nanoparticles was functionalized with two different red-emitting perylenediimide fluorophores (PDI). One glycosacharide-PDI complex has been synthesized for the first time to be labeled to apoferritin-encapsulated maghemite nanoparticles. Bifunctionality of maghemite@perylenediimide was demonstrated by both magnetic-core and fluorescent-labeled shell properties. SQUID measurements confirmed superparamagnetic behavior above 35K. Fluorescence of perylenediimides is retained once attached to the magnetic nanoparticle. Moreover, fluorescence microscopy showed that one of these fluorescent-magnetic nanoparticles was specifically internalized in bifidobacteria without affecting cell viability. These results revealed that the dual-modal imaging probes of maghemite@perylenediimide nanoparticles have the potential to be used as optical/MR dual imaging agents.

Solvent-Free Off-On Detection of the Improvised Explosive Triacetone Triperoxide (TATP) with Fluorogenic Materials

A fluorogenic perylenediimide-functionalized polyacrylate capable of generating color and fluorescence changes in the presence of triacetone triperoxide TATP), an improvised explosive used in terrorist attacks, under solvent-free, solid-state conditions has been developed. The material works by accumulating volatile TATP until it reaches a threshold; therefore, triggering colorimetric and fluorescent responses.

Direct alkylthio-functionalization of unsubstituted perylenediimides

Herein, we report a simple fluoride-mediated reaction for the direct mono- and dialkylthio-functionalization of unsubstituted perylenediimides (PDIs) under very mild conditions. The aromatic substitution reaction offers the possibility to introduce primary, secondary and, even, tertiary alkanethiols either on the 1- or on the 1,6-bay positions of unsubstituted PDIs. 1,6-DialkylthioPDIs show that absorption and fluorescence spectra shifted to the red when compared with the unsubstituted PDI, with Stokes shifts around 70-80 nm.

Fluoride-mediated alkoxylation and alkylthio-functionalization of halogenated perylenediimides

The reaction of ortho- and bay-substituted chloro- or bromoperylenediimides with alcohols and thiols in the presence of fluoride ions affords the corresponding alkoxy- or alkylthioPDIs in good to excellent yields under mild conditions.

Characterization and Polymerization of Thienylphenyl and Selenylphenyl Amines and Their Interaction with CdSe Quantum Dots

Hybrid quantum-dot-sensitized solar cells show promising novel optoelectronic properties. An adequate design of such cells requires a deep understanding of the characteristics of each component, including their interactions. In this context, the electrochemical properties of two different hole-transporting materials (HTMs) and their chemical interactions with trioctylphosphine-capped CdSe quantum dots are investigated to evaluate their potential use in hybrid quantum-dot-sensitized solar cells. Tris[4-(thien-2-yl)phenyl]amine (TTPA) and tris[4-(selen-2-yl)phenyl]amine (TSePA) are studied in the solid state as thin films deposited on a conducting substrate. Spectroelectrochemical studies evidence both solid-state electropolymerization and doping. Upon addition of TSePA or partially polymerized TTPA to a colloidal solution of trioctylphosphine-capped CdSe quantum dots, the steady-state photoluminescence is quenched. This suggests that the quantum dots and the HTM strongly interact, probably through an excited-state charge-transfer mechanism. The combination of all these pieces of information indicates that polymerized TTPA and TSePA are potential candidates as HTMs for hybrid quantum-dot-sensitized solar cells.

PHOTOCHEMISTRY OF 1, n -DIIODOALKANES

This article reviews the photochemistry of 1,n-diiodoalkanes, with special emphasis on the involved intermediates. Photolysis of 1,1-diiodomethane produces homolytic cleavage of the C–I bond to give the α-iodo radical, which in solid matrix cannot dissociate but collapses to isodiiodomethane. However, in solution subsequent electron-transfer produces the α-iodo cation, which is able to achieve cyclo-propanation of olefins. In the case of 1,2-diiodides, their photolysis gives rise to β-iodoalkyl radicals which usually lose iodine very rapidly, forming a carbon-carbon double bond. Homolytic cleavage of 1,n-diiodoalkanes (n>2) affords n-iodo radicals which are stabilized by participation of the remaining iodine atom. The cyclic hypervalent iodine radicals thus generated have low reactivity towards oxygen and characteristic UV spectra whose λmax depends on the ring size. These intermediates can be photolyzed, with iodine extrusion and formation of 1,2-diphenylcycloalkanes. On the other hand, photoinduced electron-transfer between carbanionic nucleophiles and 1,n-diiodoalkanes produces n-iodo radicals, which couple with the nucleophile leading to radical anions. Intramolecular electron-transfer from the radical anion to the σ* MO of the remaining C–I bond may compete with intermolecular electron-transfer to the substrate. This type of processes have been used for the synthesis of mono- and disubstituted adamantane derivatives. Finally, photoinduced electron-transfer between aromatic amines and 1,n-diiodoperfluoroalkanes (n>2) allows the preparation of fluorine containing heteroaromatic compounds.

Purcell-enhancement of the radiative PL decay in perylenediimides by coupling with silver nanoparticles into waveguide modes

In this work, an interesting approach to enhance the coupling between excitons and plasmons is proposed by integrating highly luminescent perylenediimides (PDIs) and Ag metal nanoparticles (MNPs) in the core of a multilayer dielectric waveguide. The combination of the weak plasmonic coupling and the high scattering of MNPs gives rise to a significant improvement of the PDI photoluminescence and Purcell factor (PF) in forward-scattering geometry. Furthermore, when the PDI-MNP system is used as the core of a multilayer waveguide, a Purcell factor enhancement larger than 10 is observed, which is explained by an increase in the exciton-plasmon coupling under the light confinement in the waveguiding structure as compared to a single layer of PDI emitters.