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1. Charge Transport in Ternary Charge‐Transfer Solid Solution Single Crystals

   https://doi.org/10.1002/adfm.202523425  

   Novak, Jonathan C; Makala, Manikanta; MacKenzie, Edith L; Coropceanu, Veaceslav; Agosto, Kimberly; Moravek, Abigail A; Jurchescu, Oana D; Wiscons, Ren A (November 2025, Advanced Functional Materials)

   Abstract The electronic effects of structural defects introduced through chemical doping are challenging to characterize in organic semiconductors, especially when measured in thin film devices where the performance is sensitive to structural heterogeneity. Here, a simple approach is presented to probe the roles of indirect and direct electronic coupling on charge transport in a series of compositionally varied charge‐transfer single crystals. In this system, carbazole (CBZ) is controllably substituted withN‐methylcarbazole (NMCBZ) in the cocrystal formed between CBZ and 1,3,4,5,7,8‐hexafluoro‐11,11,12,12‐tetracyano‐2,6‐naphthoquinodimethane (F₆TNAP), producing a series of single crystals with compositions that range between 0 – 50% CBZ replacement and preserve the structure type of the parent cocrystal. Gas‐phase electronic structure calculations predict that substitutional replacement of CBZ with NMCBZ introduces two competing effects: (i) strengthening of indirect coupling by increasing the average degree of charge transfer and (ii) weakening of direct exchange by increasing the distance between adjacent charge‐transfer π‐stacks. Charge transport measurements reveal an initial decrease in the mobility upon substitution of CBZ with NMCBZ, rationalized by a combination of hole‐trapping and weakened direct coupling with increasing NMCBZ content. Critically, these results demonstrate the potential for solid solutions to offer insight into charge transport mechanisms and their chemical tunability in molecular electronic materials. 

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2. Is it common for charge recombination to be faster than charge separation?

   https://doi.org/10.1002/kin.21285  

   Espinoza, Eli M.; Bao, Duoduo; Krzeszewski, Maciej; Gryko, Daniel T.; Vullev, Valentine I. (May 2019, International Journal of Chemical Kinetics)

   Abstract Attaining long‐lived charge‐transfer (CT) states is of the utmost importance for energy science, photocatalysis, and materials engineering. When charge separation (CS) is slower than consequent charge recombination (CR), formation of a CT state is not apparent, yet the CT process provides parallel pathways for deactivation of electronically excited systems. The nuclear, or Franck‐Condon (FC), contributions to the CT kinetics, as implemented by various formalisms based on the Marcus transition‐state theory, provide an excellent platform for designing systems that produce long‐lived CT states. Such approaches, however, tend to underestimate the complexity of alternative parameters that govern CT kinetics. Here we show a comparative analysis of two systems that have quite similar FC CT characteristics but manifest distinctly different CT kinetics. A decrease in the donor‐acceptor electronic coupling during the charge‐separation step provides an alternative route for slowing down undesired charge recombination. These examples suggest that, while infrequently reported and discussed, cases where CR is faster than CS are not necessarily rare occurrences. 

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3. Effects of charge fluctuation and charge regulation on the phase transitions in stoichiometric VO2

   https://doi.org/10.1038/s41598-020-73447-9  

   Joshi, Siddharth; Smieszek, Nicholas; Chakrapani, Vidhya (October 2020, Scientific Reports)

   Abstract Detailed electrical and photoemission studies were carried out to probe the chemical nature of the insulating ground state of VO₂, whose properties have been an issue for accurate prediction by common theoretical probes. The effects of a systematic modulation of oxygen over-stoichiometry of VO₂from 1.86 to 2.44 on the band structure and insulator–metal transitions are presented for the first time. Results offer a different perspective on the temperature- and doping-induced IMT process. They suggest that charge fluctuation in the metallic phase of intrinsic VO₂results in the formation of e⁻and h⁺pairs that lead to delocalized polaronic V³⁺and V⁵⁺cation states. The metal-to-insulator transition is linked to the cooperative effects of changes in the V–O bond length, localization of V³⁺electrons at V⁵⁺sites, which results in the formation of V⁴⁺–V⁴⁺dimers, and removal of$$\pi^{*}$$ ${\pi }^{\ast }$screening electrons. It is shown that the nature of phase transitions is linked to the lattice V³⁺/V⁵⁺concentrations of stoichiometric VO₂and that electronic transitions are regulated by the interplay between charge fluctuation, charge redistribution, and structural transition. 

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4. Charge‐Transport Properties of F ₆ TNAP‐Based Charge‐Transfer Cocrystals

   https://doi.org/10.1002/adfm.201904858  

   Dasari, Raghunath_R; Wang, Xu; Wiscons, Ren_A; Haneef, Hamna_F; Ashokan, Ajith; Zhang, Yadong; Fonari, Marina_S; Barlow, Stephen; Coropceanu, Veaceslav; Timofeeva, Tatiana_V; et al (October 2019, Advanced Functional Materials)

   Abstract The crystal structures of the charge‐transfer (CT) cocrystals formed by the π‐electron acceptor 1,3,4,5,7,8‐hexafluoro‐11,11,12,12‐tetracyanonaphtho‐2,6‐quinodimethane (F₆TNAP) with the planar π‐electron‐donor molecules triphenylene (TP), benzo[b]benzo[4,5]thieno[2,3‐d]thiophene (BTBT), benzo[1,2‐b:4,5‐b′]dithiophene (BDT), pyrene (PY), anthracene (ANT), and carbazole (CBZ) have been determined using single‐crystal X‐ray diffraction (SCXRD), along with those of two polymorphs of F₆TNAP. All six cocrystals exhibit 1:1 donor/acceptor stoichiometry and adopt mixed‐stacking motifs. Cocrystals based on BTBT and CBZ π‐electron donor molecules exhibit brickwork packing, while the other four CT cocrystals show herringbone‐type crystal packing. Infrared spectroscopy, molecular geometries determined by SCXRD, and electronic structure calculations indicate that the extent of ground‐state CT in each cocrystal is small. Density functional theory calculations predict large conduction bandwidths and, consequently, low effective masses for electrons for all six CT cocrystals, while the TP‐, BDT‐, and PY‐based cocrystals are also predicted to have large valence bandwidths and low effective masses for holes. Charge‐carrier mobility values are obtained from space‐charge limited current (SCLC) measurements and field‐effect transistor measurements, with values exceeding 1 cm²V⁻¹s¹being estimated from SCLC measurements for BTBT:F₆TNAP and CBZ:F₆TNAP cocrystals. 

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5. Effective interactions, structure, and pressure in charge-stabilized colloidal suspensions: Critical assessment of charge renormalization methods

   https://doi.org/10.1063/5.0180914  

   Brito, Mariano E; Nägele, Gerhard; Denton, Alan R (November 2023, The Journal of Chemical Physics)

   Charge-stabilized colloidal suspensions display a rich variety of microstructural and thermodynamic properties, which are determined by electro-steric interactions between all ionic species. The large size asymmetry between molecular-scale microions and colloidal macroions allows the microion degrees of freedom to be integrated out, leading to an effective one-component model of microion-dressed colloidal quasi-particles. For highly charged colloids with strong macroion–microion correlations, nonlinear effects can be incorporated into effective interactions by means of charge renormalization methods. Here, we compare and partially extend several practical mean-field methods of calculating renormalized colloidal interaction parameters, including effective charges and screening constants, as functions of concentration and ionic strength. Within the one-component description, we compute structural and thermodynamic properties from the effective interactions and assess the accuracy of the different methods by comparing predictions with elaborate primitive-model simulations [P. Linse, J. Chem. Phys. 113, 4359 (2000)]. We also compare various prescriptions for the osmotic pressure of suspensions in Donnan equilibrium with a salt ion reservoir and analyze instances where the macroion effective charge becomes larger than the bare one. The methods assessed include single-center cell, jellium, and multi-center mean-field theories. The strengths and weaknesses of the various methods are critically assessed, with the aim of guiding optimal and accurate implementations. 

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