Dual Charge Transfer Generated from Stable Mixed-Valence Radical Crystals for Boosting Solar-to-Thermal Conversion

Tuning (Photo)Electronic Properties of an Electron Deficient Porous Polymer via n-Doping with Tetrathiafulvalene

Charge-transfer complex formation within the pores of porous polymers is an efficient way to tune their electronical properties. Introduction of electron accepting guests to the electron donating hosts to conduct their p-doping is intensively studied in this context. However, the vice versa scenario, n-doping by treating the electron deficient (i.e., n-type) porous polymers with electron donating dopants, is rare. In this work, synthesis of an n-type phenazine based conjugated microporous polymer and its exposure to strong electron donating tetrathiafulvalene (TTF) dopants are presented. The fundamental physical characterizations (e.g., elemental analysis, gas sorption) showed that the vacuum impregnation technique is a good approach to load the guest molecules inside the pores. Moreover, the formation of charge-transfer complexes between the phenazine building blocks of the polymeric network and TTF dopants are confirmed via spectral techniques such Fourier transform infra-red, UV-vis, steady-state/time-resolved photoluminescence, and transient absorbance spectroscopies. Effect of the doping to the electronical properties is monitored by employing photoelectrochemical measurements, which showed lower charge-transfer resistivity and nearly doubled photocurrents after the doping. The study is, therefore, an important advancement for the applicability of (n-type) porous polymeric materials in the field of photo(electro)catalysis and organic electronics.

Charge-Transfer Complexes: Halogen-Doped Anthracene as a Case of Study

Charge transfer (CT) crystals exhibit unique electronic and magnetic properties with interesting applications. We present a rational and easy guide which allows to foresee the effective charge transfer co-crystal production and that is based on the comparison of the frontier molecular orbital (MO) energies of a donor and acceptor couple. For the sake of comparison, theoretical calculations have been carried out by using the cheap and fast PM6 semiempirical Hamiltonian and pure HF/cc-pVTZ level of the theory. The results are then compared with experimental results obtained both by chemical (bromine and iodine were used as the acceptor) and electrochemical doping (exploiting an original experimental set-up by this laboratory: the electrochemical transistor). Infra-red vibrational experimental results and theoretically calculated spectra are compared to assess both the effective donor-acceptor (D/A) charge-transfer and transport mechanism (giant IRAV polaron signature). XPS spectra have been collected (carbon (1 s) and iodine (3d5/2)) signals, yielding further evidence of the effective formation of the CT anthracene:iodine complex.

Stable Radicals in Dihydrophenazine Derivatives-Doped Epoxy Resin for High Photothermal Conversion

Organic radicals exhibit great potential in photothermal applications, however, their innate high reactivity with oxygen renders the preparation of stable organic radicals highly challenging. In this work, a series of co-doped radical polymers ares prepared by doping dihydrophenazine derivatives (DPPs) into the epoxy resin matrix. DPPs can form radical species through the electron transfer process, which are further stabilized by the complex 3D network structure of epoxy resin. Experimental results show that the photothermal conversion efficiency is as high as 79.9%, and the temperature can quickly rise to ≈130 °C within 60 s. Due to the excellent visible light transmittance and mechanical properties of co-doped systems, this study further demonstrates their practical applications in energy-saving solar windows and thermoelectric power generation.

Mixed-Valence BN-Doped Corannulene Trimer Radical Cations

Mixed-valence (MV) dimers have been extensively investigated, however, the structure and properties of purely organic MV trimers based on open-shell polycyclic aromatic hydrocarbons remain elusive. Herein, unprecedented MV BN-doped corannulene radical cations [BN-Cor1]3 ⋅⋅2+  ⋅ 2[BArylF 4 ]- and [BN-Cor2]3 ⋅⋅2+  ⋅ 2[BArylF 4 ]- were synthesized via chemical oxidation, and their structures were unambiguously confirmed by single-crystal X-ray diffraction. These uncommon radical cations consist of three corannulene cores and two [BArylF 4 ]- anions, and three corannulene motifs [BN-Cor1]3 ⋅⋅2+ and [BN-Cor2]3 ⋅⋅2+ in the unit cell exhibit a trimer structure with a slipped π-stacking configuration. Detailed structural analyses further revealed that the corannulene cores exhibit an infinite layered self-assembly configuration, allowing their potential applications as building blocks for molecular conductors. The detection of a forbidden transition (Δms =±2) by electron paramagnetic resonance (EPR) spectroscopy further confirmed the existence of two unpaired electrons in the π-trimers and the MV characteristic of these two species. Variable-temperature EPR and conductivity measurements suggested that the BN-doped π-trimers exhibited antiferromagnetic coupling and conductivity properties.

DFT investigations of phenyldithiafulvene dimers at different oxidation states

Oxidative dimerization of aryl-substituted dithiafulvenes (Ar-DTFs) presents an efficient C-C bond forming method for the preparation of diverse redox-active π-conjugated molecules and conductive polymers. Previous experimental data indicated a reaction pathway in which direct combination of two Ar-DTF radical cations is a key step. However, mechanistic details about how Ar-DTF dimers are formed under different oxidation states have not yet been clearly established prior to this work. The assembly of two Ar-DTF molecules generates a vast conformational and configurational landscape, which is quite complex but fundamentally important for understanding the dimerization mechanism. To cast a deep insight into this aspect, we have performed density functional theory (DFT) calculations at the M06-2X/Def2-SVP level of theory to thoroughly investigate the potential energy surfaces (PESs) of various dimers of a phenyl-substituted dithiafulvene (Ph-DTF) in the mixed-valence radical cation and dication states. Key stationary points in these PESs, including minimum-energy conformers (π-dimers and σ-dimers) as well as the transition states connected to them, were examined and compared. We have also calculated the binding energies of these dimers to evaluate the energetic driving forces for their formation. Based on our computational results, the roles that various Ph-DTF dimers play in different pathways of oxidative dimerization have been clarified.