In this review article, we highlight over 25 years of fullerene research in charge transfer chemistry. The major thrust of this work is to illustrate interfacial interactions between fullerenes and porphyrins in electron donor-acceptor conjugates as well as self-assembled associates and co-crystallites all the way to organic photovoltaics. Hereby, the analysis of the fundamental proceses, namely, energy transfer, charge shift, charge separation as well as charge recombination stand at the forefront. Our examples, illustrate on how fine-tuning the structure leads to substantial alteration of interfacial interactions.

We report here a new expanded tetrathiafulvalene-(exTTF)-porphyrin scaffold, 2, that acts as a ball and socket receptor for C 60 and C 70 . Supramolecular interactions between 2 and these fullerenes serve to stabilize three-dimensional (3D) supramolecular organic frameworks (SOFs) in the solid state formally comprising peapod-like linear assemblies. The SOFs prepared via self-assembly in this way act as "tunable functional materials" wherein the complementary geometry of the components and the choice of fullerene play crucial roles in defining the conductance properties. The highest electrical conductivity ( = 1.3  10 -8 S cm -1 at 298 K) was observed in the case of the C70-based SOF. In contrast low conductivity was seen for the SOF based on pristine 2 ( = 5.9  10 -11 S cm -1 at 298 K). The conductivity seen for the C 70 -based SOF approaches that seen for other TTF-and fullerene-based supramolecular materials in spite of the fact that the present systems are metal-free and constructed entirely from neutral building blocks. Transient absorption spectroscopic (TAS) measurements corroborated the formation of charge transfer (CT) states (i.e., 2 + /C60 and 2 + /C70 -, respectively), rather than fully charge separated states (i.e., 2 •+ /C 60 •and 2 •+ /C 70 •-, respectively) both in solution (toluene and benzonitrile) and in the solid state at 298 K. Such findings are considered consistent with an ability to transfer charges effectively over long distances within the present SOFs, rather than, e.g., the formation of energetically trapped ionic species. important implications for the design of new organic charge transport devices and could lead to the development of new highly conductive organic materials based entirely on neutral building blocks. ASSOCIATED CONTENT Supporting InformationThe supplementary information and chemical compound information are available in the online version of the paper. Crystallographic data have been deposited with the Cambridge Crystallographic Data Centre under reference numbers CCDC-1970803, 1991548 and 1991549. Reprints and permissions information is available online at https://pubs.acs.org. Correspondence and requests for materials should be addressed to A

We report evidence of excited-state ion pair reorganisation in a cationic iridium (III) photoredox catalyst in 1,4-dioxane. Microwave-frequency dielectric-loss measurements combined with accurate calculations of dipolar relaxation time allow us to assign both ground and excited-state molecular dipole moments in solution and determine the polarizability volume in the excitedstate. These measurements show significant changes in ground-state dipole moment between [Ir[dF(CF 3 )ppy] 2 (dtbpy)]PF 6 (10.74 Debye) and [Ir[dF(CF 3 )ppy] 2 (dtbpy)]BAr F 4 (4.86 Debye). Photoexcitation of each complex results in population of highly mixed ligand centered and metal-to-ligand charge transfer states with enormous polarizability. Relaxation to the lowest lying excited-state leads to a negative change in the dipole moment for [Ir[dF(CF 3 )ppy] 2 (dtbpy)]PF 6 , and a positive change in dipole moment for [Ir[dF(CF 3 )ppy] 2 (dtbpy)]BAr F 4 . These observations are consistent with a sub-nanosecond reorganization with the PF − 6 counter-ion, which cancels the dipole moment of the lowest lying excited-state, a process which is absent for the BAr F− 4 counter-ion. Taken together, these observations suggest contact-ion pair formation between the cationic metal complex and the PF − 6 anion and, at most, solvent-separated pairing with BAr F− 4 . The dynamic ion pair reorganisation we observe with the PF − 6 counter-ion may substantially modify both the thermodynamic potential available for electron transfer and kinetically inhibit oxidative catalysis, as the anion moves to cover the positively charged end of the molecule, providing a possible mechanistic explanation for recently observed trends in the catalytic activity of these complexes as a function of anion identity in low-polarity solvents. These tunable ion-pair dynamics could prove to be a valuable tool for tailoring the reactivity of both new and extant photocatalysts.

Upon photoinitiated electron transfer, charge recombination limits the quantum yield of photoredox reactions for which the rates for the forward reaction and back electron transfer are competitive. Taking inspiration from a proton-coupled electron transfer (PCET) process in Photosystem II, a benzimidazole-phenol (BIP) has been covalently attached to the 2,2′-bipyridyl ligand of [Ir(dF(CF 3 )ppy) 2 (bpy)][PF 6 ] (dF(CF 3 )ppy = 2-(2,4-difluorophenyl)-5-(trifluoromethyl)pyridine; bpy = 2,2′-bipyridyl). Excitation of the [Ir(dF(CF 3 )ppy) 2 (BIP-bpy)][PF 6 ] photocatalyst results in intramolecular PCET to form a charge-separated state with oxidized BIP. Subsequent reduction of methyl viologen dication (MV 2+ ), a substrate surrogate, by the reducing moiety of the charge separated species demonstrates that the inclusion of BIP significantly slows the charge recombination rate. The effect of ∼24-fold slower charge recombination in a photocatalytic phthalimide ester reduction resulted in a greater than 2-fold increase in reaction quantum efficiency.

Carbon laser-patterning (CLaP) is emerging as a new tool for the precise and selective synthesis of functional carbon-based materials for on-chip applications. The aim of this work is to demonstrate the applicability of laser-patterned nitrogen-doped carbon (LP-NC) for resistive gas-sensing applications. Films of pre-carbonized organic nanoparticles on polyethylenetherephthalate are carbonized with a CO 2 -laser. Upon laser-irradiation a compositional and morphological gradient in the films is generated with a carbon content of 92% near the top surface. The specific surface areas of the LP-NC are increased by introducing sodium iodide (NaI) as a porogen. Electronic conductivity and surface area measurements corroborate the deeper penetration of the laser-energy into the film in the presence of NaI. Furthermore, impregnation of LP-NC with MoC 1−x (<10 nm) nanoparticles is achieved by addition of ammonium heptamolybdate into the precursor film. The resulting dopingsensitive nano-grain boundaries between p-type carbon and metallic MoC 1−x lead to an improvement of the volatile organic compounds sensing response of ΔR/R 0 = −3.7% or −0.8% for 1250 ppm acetone or 900 ppm toluene at room temperature, respectively, which is competitive with carbon-based sensor materials. Further advances in sensitivity and in situ functionalization are expected to make CLaP a useful method for printing selective sensor arrays.

Star-shaped magnesium porphyrins with four diketopyrrolopyrrole units conjugated by four ethynyl linkers work as electron donors for organic solar cells.

A relative humidity sensor was produced by carbon laser patterning of a carbon precursor ink on a flexible substrate. Citric acid and urea, both inexpensive and naturally abundant molecules, are used as initial precursors to obtain a porous carbon foam after CO 2 laser irradiation. The laser-patterned material is characterized by electron microscopy, Raman spectroscopy, and vertical scanning interferometry. An intrinsic p-type semiconducting behavior was confirmed by thermoelectric and Hall measurements. The resistance of this porous, metal-free material is sensitive to atmospheric variations, namely, temperature and relative humidity (≈5 Ω•%). Under dry atmosphere, the sensor acts as a thermometer with a linear relationship between temperature and relative variation of resistance (0.07%•K −1 ). The evolution of the sensor resistance at different relative humidities and temperatures is studied by electrical impedance measurements. The kinetic transitory regime of water desorption from the carbonaceous surface of the sensor is analyzed using Langmuir's model. The equilibrium constant of adsorption K ads has been determined, and the standard enthalpy of adsorption of water on the sensor surface is estimated at Δ ads H°= −42.6 kJ•mol −1 . The simple and inexpensive production and its high, stable sensitivity make laser-patterned carbon interesting for humidity sensing applications, and the method allows for the large-scale production of printed sensor arrays.

There are notably few literature reports of electron donor-acceptor oligoynes although they offer unique opportunities for studying charge transport through 'all-carbon' molecular bridges. In this context, the current study focuses on a series of carbazole-(C≡C) n -2,5-diphenyl-1,3,4-oxadiazoles (n = 1-4) as conjugated π-systems, in general, and explores their photophysical properties, in particular. Contrary to the behavior of typical electron donor-acceptor systems, for these oligoynes the rates of charge recombination after photoexcitation increase with increasing electron donoracceptor distance. To elucidate this unusual performance, detailed photophysical and time-dependent density functional theory investigations were conducted. Significant delocalization of the electron density along the bridge indicates that the bridging states come into resonance with either the electron donor or acceptor, thereby accelerating the charge transfer. Moreover, the calculated bond lengths reveal a reduction in bond length alternation upon photoexcitation, indicating significant cumulenic character of the bridge in the excited state. In short, strong vibronic coupling between the electrondonating N-arylcarbazoles and the electron-accepting 1,3,4-oxadiazoles accelerates the charge recombination as the oligoyne becomes longer.