TTF Molecules Research Articles

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

Realizing dual charge transfer (CT) based on stable organic radicals in one system is a long-sought goal, however, remains challenging. In this work, a stable mixed-valence radical crystal is designed via a surfactant-assisted method, namely TTF-(TTF+• )2 -RC (where TTF = tetrathiafulvalene), containing dual CT interactions. The solubilization of surfactants enables successful co-crystallization of mixed-valence TTF molecules with different polarity in aqueous solutions. Short intermolecular distances between adjacent TTF moieties within TTF-(TTF+• )2 -RC facilitate both inter-valence CT (IVCT) between neutral TTF and TTF+• , and inter-radical CT (IRCT) between two TTF+• in radical π-dimer, which are confirmed by single-crystal X-ray diffraction, solid-state absorption, electron spin resonance measurements, and DFT calculations. Moreover, TTF-(TTF+• )2 -RC reveals an open-shell singlet diradical ground state with the antiferromagnetic coupling of 2J = -657 cm-1 and an unprecedented temperature-dependent magnetic property, manifesting the main monoradical characters of IVCT at 113-203 K while the spin-spin interactions in radical dimers of IRCT are predominant at 263-353 K. Notably, dual CT characters endow TTF-(TTF+• )2 -RC with strong light absorption over the full solar spectrum and outstanding stability. As a result, TTF-(TTF+• )2 -RC exhibits significantly enhanced photothermal property, an increase of 46.6°C within 180 s upon one-sun illumination.

Non-covalent Functionalization of Pristine and Defective WSe2 by Electron Donor and Acceptor Molecules

Two-dimensional transition-metal dichalcogenide (2D-TMD) monolayers have recently attracted growing interest, thanks to their excellent optoelectronic properties, especially a moderate direct band gap in the visible spectral range and an extremely strong light–matter interaction. Herein, by means of density functional theory (DFT) and ab initio molecular dynamics (AIMD), we systematically investigate the chemical doping of the WSe2 monolayer upon non-covalent attachment of electron donor and acceptor molecules, namely, fullerenes (C20, C26, and C60), tetrathiafulvalene (TTF), 7,7,8,8-tetracyanoquinodimethane (TCNQ), and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ). Our results confirm that the physisorbed molecules stack on WSe2 via a weak van der Waals interaction; this precludes any significant damage in the basal-plane structure of the monolayer. In turn, the modifications in the carrier density in the WSe2 monolayer due to organic dopants result in a change of the work function by up to 0.41 eV. By performing AIMD calculations, we show that the effect is more pronounced upon increasing the coverage density of physisorbed TTF and TCNQ molecules. The impact of Se-vacancy (VSe) defects on the electronic properties of the WSe2 monolayer and thermodynamic stability of physisorption (including the molecular density) is also considered. Interestingly, the molecules demonstrate an ability to modulate the degree of spatial localization of VSe trap states. Moreover, the shift of the Fermi level upon molecular adsorption also enables further stabilization of charged defect states associated to a VSe vacancy. The pronounced effect of molecular adsorption on the VSe defect behavior in WSe2 might open the door for potential engineering of defect states in 2D TMDs.

Interface design of the thermoelectric transport properties of phosphorene-tetrathiafulvalene nanoscale devices.

Interface design and energy band engineering are two key strategies for improving the thermoelectric conversion efficiency of low dimensional nanoscale devices. By using first-principle-based density functional theory combined with a non-equilibrium Green function method, the thermoelectric properties of a single tetrathiafulvalene (TTF) molecule coupled with armchair phosphorene nanoribbons (APNRs) within different interface modes have been investigated. The results indicate that phonon transport can be dramatically suppressed in this intermediate weak-coupling system due to strong interfacial phonon scattering behavior, where very few phonons can propagate through two nonbonded interface regions from left side lead to a TTF molecule and then to right side lead. Furthermore, connecting a thiophene group at both the head and tail of the intermediate TTF molecule can significantly enhance the power factor (S2σ) of such a weak-coupling system based on an out-of-plane electronic transmission mechanism, and there is obvious charge transfer from S atoms to upper and lower APNRs. Compared to a single regular method, composite interface co-design can achieve more accurate control of thermal/electrical transmission performance. Electrical conductance can be effectively improved with low phonon thermal conductance being maintained at the same time, and an excellent thermoelectric figure of merit (ZT) of 0.73 has been obtained near 0.6 eV.

Electronic structures and molecular doping of germanane regulated by hydrogen vacancy clusters

Germanane is expected to substitute for existing silicon-based or germanium-based material. Germanane is regarded as an ideal candidate for next-generation semiconductor material due to its suitable band gap, high electron mobility, better environmental stability, small electrical noise and ultrathin geometry. In this work, the effects of different configuration and concentration of hydrogen vacancy cluster on the electronic properties of germanane and its molecular doping are systematically investigated through the first-principles method based on density functional theory and none-quilibrium Green’s function. The results show that the hydrogen vacancy clusters with different configurations can induce magnetism with different characteristics in Germanane<sub>Dehydrogenated-<i>x</i>H</sub> (G<sub>D-<i>x</i>H</sub>) system, and the magnetic moments are consistent with the predictions of Lieb’s theorem. Moreover, the p-type-liked doping effects caused by defective state under G<sub>D-<i>x</i>H</sub> (<i>x</i> = 1, 4, 6) systems can be realized in their spin-down band structures. The corresponding energy values for exciting electron would gradually decrease with the increase of the concentration of hydrogen vacancy clusters under different configurations. After adsorbing tetrathiafulvalene (TTF) molecules, G/TTF and G<sub>D-<i>x</i>H</sub>/TTF (<i>x</i> = 1, 2, 6) systems exhibit molecular doping characteristics induced by the TTF molecules. More importantly, for G<sub>D-<i>x</i>H</sub>/TTF (<i>x</i> = 1, 6) system, the different molecular doping types can be introduced in spin-up and spin-down band structures due to the hybridization composed of molecular orbitals and defective states under spin polarization. Further calculations of their transport properties indicate that germanane-based device with Armchair and Zigzag configurations both exhibit intensive isotropy, and the performance of <i>I-V</i> characteristics can be dramatically enhanced owing to the carrier doping by TTF adsorption.

Electronic Structure and IR Spectra Analysis of Tetrathiafulvelene (TTF) Using RHF and DFT Quantum Mechanical Methods

Tetrathiafulvalene (C6H4S4) is an organosulfur compound used in the manufacture of organic optoelectronic materials. Restricted Hartree-Fock (RHF) and Density Functional Theory (DFT) were employed for the study of the optimized molecular structure of TTF using different basis sets. All computations were performed using Gaussian 03 package. Parameters such as minimum energy, bond lengths and bond angles, HOMO-LUMO energy gap, chemical reactivity descriptors, Non-linear optical properties (such as isotropic polarizability (α), anisotropy of polarizability (∆∝), and total first hyper-polarizability (βtot)), density of states, vibrational frequencies, and intensities were computed and reported in order to determine the relative stability as well as chemical reactivity of the molecule. The results obtained show that RHF has the lowest average value of bond length of 1.0729Å while that obtained using DFT has the lowest average value of 1.0812Å using the same basis set 6-311++G (d, p). This shows that the value is a bit higher using DFT than RHF which implies that the bonds of TTF molecule will be slightly stronger when optimized using RHF than DFT. The bond angles were found to be slightly higher by using DFT than RHF. The calculated HOMO-LUMO energy gap shows that the molecule will be slightly more stable in chemical reaction using RHF than DFT. The DFT values, 3.59 eV and 3.60 eV obtained for the energy gap are closer to the reported value of 3.63eV compared to those obtained by RHF. From the results obtained for vibrational frequencies using both methods, TTF is stable due to the absence of imaginary frequencies. This confirms the stability of the molecule as stated in the results of HOMO-LUMO energy gap. The calculated vibrational frequencies show that the most intense frequency was obtained to be 752.6293 cm-1 at corresponding intensity of 145.9063KM/mole by RHF/6-31++G (d, p) while at B3LYP/6-31+G(d), the most intense frequency is about 635.0243 cm-1 with corresponding intensity of 138.5738MK/mole. By and large, the studyunveil the potential of Tetrathiafulvalene for optoelectronic applications.

Computational Discovery of TTF Molecules with Deep Generative Models.

We present a computational workflow based on quantum chemical calculations and generative models based on deep neural networks for the discovery of novel materials. We apply the developed workflow to search for molecules suitable for the fusion of triplet-triplet excitations (triplet-triplet fusion, TTF) in blue OLED devices. By applying generative machine learning models, we have been able to pinpoint the most promising regions of the chemical space for further exploration. Another neural network based on graph convolutions was trained to predict excitation energies; with this network, we estimate the alignment of energy levels and filter molecules before running time-consuming quantum chemical calculations. We present a comprehensive computational evaluation of several generative models, choosing a modification of the Junction Tree VAE (JT-VAE) as the best one in this application. The proposed approach can be useful for computer-aided design of materials with energy level alignment favorable for efficient energy transfer, triplet harvesting, and exciton fusion processes, which are crucial for the development of the next generation OLED materials.

Effective Doping of Square/Octagon‐Phase Arsenene by Adsorption of Organic Molecules

AbstractAdsorption of organic molecules can be a better choice than traditional chemical doping to achieve effective doping of 2D materials. The adsorption of organic molecules on square/octagon‐phase (S/O‐phase) arsenene is investigated and promoted the possibility of developing p–n junctions. In particular, it is found that adsorption of F4‐TCNQ or TCNE molecules leads to effective p‐doping. Adsorption of DMPD or TTF molecules leads to less effective n‐doping. Interestingly, in the case of TTF adsorption strain engineering can be used to greatly improve the material properties. Therefore, both effective n‐ and p‐doping of S/O‐phase arsenene can be realized.

Effect of the protection layer formed by cross-linked gelatin on the stability and performance of glucose and oxygen fuel cells

A glucose oxidation catalyst comprising carbon nanotube, tetrathiafulvalene (TTF), gelatin, glutaraldehyde (GA) and glucose oxidase (GOx) (CNT/[TTF-GOx]/Gelatin + GA) is suggested to enhance the reactivity of glucose oxidation reaction (GOR), and the performance and stability of enzymatic biofuel cells (EBCs) using this catalyst. In this catalyst, TTF is used as mediator to transfer electron effectively, while GA is crosslinked to gelatin to form non-soluble network. The structure prevents the dissolution of gelatin from aqueous electrolyte and reduces the leaching-out of GOx and TTF molecules. To confirm the crosslinking effect of GA and gelatin, Fourier-transform infrared spectroscopy (FT-IR) and electrochemical evaluations are utilized. According to FT-IR analysis, it was observed that the amide I peak shifted after crosslinking. This is evidence showing the appropriate network formation and the reactivity of CNT/[TTF-GOx]/Gelatin + GA is well preserved even after multiple potential cycling. In addition, its GOx activity is regularly monitored for one month and the measurements prove that the structure prevents the leaching out of GOx molecules. Based on that, EBC using the anodic catalyst shows excellent performances, such as open circuit voltage of 0.75 V and maximum power density of 184 μW/cm2.

Noncovalently functionalization of Janus MoSSe monolayer with organic molecules

Because the crystal structure of Janus MoSSe is between from MoS 2 and MoSe 2 , and the Janus MoSSe probably exhibited to outstanding characteristics difference from MoS 2 and MoSe 2 . Adsorption of organic molecules is a prospective and effective pattern to modify the optoelectronic properties of 2D materials . For this purpose, the optical and electronic characteristics of organic molecules adsorbed Janus MoSSe monolayer were discussed by the first principles calculations. The results indicate that p -doped Janus MoSSe can be obtained by molecular doping with tetracyanoquinodimethane (TCNQ) and tetracyanoethylene (TCNE), whereas n -doped Janus MoSSe can be realized by doping with tetrathiafulvalene (TTF). Importantly, a dipole moment is produced between Janus MoSSe and organic molecule, and the dipole moment can to a great extent alter the work function values of Janus MoSSe ranged from 3.76 eV to 6.17 eV. Interestingly, the impurity band near the Fermi level appears in the band structures of Janus MoSSe after different organic molecules adsorption, which demonstrates that electron is more prone to transition. Furthermore, Adsorption of organic molecules on Janus MoSSe can significantly expand its optical absorption spectrum in the visible light region. This study gives a theoretical guidance for the fabrication of Janus MoSSe-based photovoltaics nanodevices . • Effective p-type doping of MoSSe can be realized by adsorption of TCNE and TCNQ molecules, while n-doped MoSSe can be obtained by adsorption of TTF molecule. • A dipole moment is formed between organic molecule and Janus MoSSe, and this dipole moment can significantly tune the work function values of Janus MoSSe. • Adsorption of organic molecules on Janus MoSSe can significantly expand its optical absorption spectrum in the visible light region.

Supramolecular Tessellations by a Rigid Naphthalene Diimide Triangle.

Tessellation of organic polygons though [π···π] and charge-transfer (CT) interactions offers a unique opportunity to construct supramolecular organic electronic materials with 2D topologies. Our approach to exploring the 3D topology of 2D tessellations of a naphthalene diimide-based molecular triangle (NDI-Δ) reveals that the 2D molecular arrangement is sensitive to the identity of the solvent and solute concentrations. Utilization of nonhalogenated solvents, combined with careful tailoring of the concentrations, results in NDI-Δ self-assembling though [π···π] interactions into 2D honeycomb triangular and hexagonal tiling patterns. Cocrystallization of NDI-Δ with tetrathiafulvalene (TTF) leads systematically to the formation of 2D tessellations as a result of superstructure-directing CT interactions. Different solvents lead to different packing arrangements. Using MeCN, CHCl3, and CH2Cl2, we identified three sets of cocrystals, namely CT-A, CT-B, and CT-C, respectively. Solvent modulation plays a critical role in controlling not only the NDI-Δ:TTF stoichiometric ratios and the molecular arrangements in the crystal superstructures, but also prevents the inclusion of TTF guests inside the cavities of NDI-Δ. Confinement of TTF inside the NDI-Δ cavities in the CT-A superstructure enhances the CT character with the observation of a broad absorption band in the NIR region. In the CT-B superstructure, the CHCl3 lattice molecules establish a set of [Cl···Cl] and [Cl···S] intermolecular interactions, leading to the formation of a hexagonal grid of solvent in which NDI-Δ forms a triangular grid. In the CT-C superstructure, three TTF molecules self-assemble, forming a supramolecular isosceles triangle TTF-Δ, which tiles in a plane alongside the NDI-Δ, producing a 3 + 3 honeycomb tiling pattern of the two different polygons. Solid-state spectroscopic investigations on CT-C revealed the existence of an absorption band at 2500 nm, which on the basis of TDDFT calculations, was attributed to the mixed-valence character between two TTF•+ radical cations and one neutral TTF molecule.

Accessing New Charge-Transfer Complexes by Mechanochemistry: A Tetrathiafulvalene Chloranilic Acid Polymorph Containing Segregated Tetrathiafulvalene Stacks

Two polymorphs of tetrathiafulvalene chloranilic acid (TTF-CAH2) have been synthesized by mechanochemistry. The previously known "ionic" polymorph (form I) was prepared by liquid-assisted grinding (LAG) using various highly polar solvents as well as protic but moderately polar solvents, such as alcohols of one to four carbon atoms. A new TTF-CAH2 polymorph (form II) was obtained by LAG and slurry mechanochemistry using aprotic, low-polarity solvents, as well as nonpolar solvents and neat grinding. The crystal structure of the new TTF-CAH2 polymorph was determined from the combined analysis of synchrotron powder X-ray diffraction and neutron powder diffraction data at room temperature. The material displays segregated stacks of TTF and CAH2 molecules. Fourier transform infrared spectroscopy as a function of the temperature (10-300 K) indicates that TTF-CAH2 form II is an electrical semiconductor with a small band gap of ∼0.115 eV (versus ∼0.146 eV for the "ionic" form I), and there is no indication of phase transitions in that temperature interval. The examination of the frequency regions wherein the absorption bands of TTF and TTF+• species occur suggests that TTF-CAH2 form II is most likely a neutral phase.

Exploring the Structure, Electron Density and HOMO-LUMO Studies of Tetrathiafulvalene (TTF) as Organic Superconductors: A DFT and AIM Analysis

The Structure, Electron density and HOMO-LUMO analysis of TTF molecule was carefully evaluated by ab initio (HF) and density functional theory (B3LYP) calculations. The optimized (HF/6-311G** and B3LYP/6-311G**, B3LYP/auf-cc-PVDZ) geometric parameters are in excellent agreement with the similar type experimental data. For both levels of calculation, the low charge accumulation have C\(-\)S and C\(\equiv\)N bonds, at the bond critical point, which gives that the bond charges are highly depleted compared with all other bonds in the molecule. Further, AIM theory shows the difference of charge distribution in all bonds. The molecular conductivity (HOMO-LUMO gap) properties are solely related to the ESP of the entire system. The ionization potential gives the very good information of conductivity. These observations give an insight on this kind of super conducting material, which are useful to design navel electronic devices.

Study of stacking interactions between two neutral tetrathiafulvalene molecules in Cambridge Structural Database crystal structures and by quantum chemical calculations.

Tetrathiafulvalene (TTF) and its derivatives are very well known as electron donors with widespread use in the field of organic conductors and superconductors. Stacking interactions between two neutral TTF fragments were studied by analysing data from Cambridge Structural Database crystal structures and by quantum chemical calculations. Analysis of the contacts found in crystal structures shows high occurrence of parallel displaced orientations of TTF molecules. In the majority of the contacts, two TTF molecules are displaced along their longer C2 axis. The most frequent geometry has the strongest TTF-TTF stacking interaction, with CCSD(T)/CBS energy of -9.96 kcal mol-1. All the other frequent geometries in crystal structures are similar to geometries of the minima on the calculated potential energy surface.

Strain-tunable molecular doping in germanane: a first-principles study

Germanane, fully hydrogenated germanene, has recently attracted great interest, both theoretical and experimental. In this paper we thoroughly study strain-tunable n/p-type doping in germanane by adsorption of tetrathiafulvalene (TTF)/tetracyanoquinodimethane (TCNQ) molecules through first-principles calculations. The results show that both TTF and TCNQ molecules can non-covalently functionalize the electronic properties of germanane. Not surprisingly, TTF molecular adsorption induces n-type doping in germanane because the TTF molecule is a typical electron donor. Moreover, a linearly tunable band gap of germanane and differing n-type doping strengths can be realized by a biaxial strain ranging from −3% to 3%. Analysis indicates that tensile strain would promote the doping effect whereas compressive strain would inhibit it. Comparatively, TCNQ molecular adsorption induces a germanane/TCNQ system which exhibits metallic characteristics. Surprisingly, however, under a tensile strain of 2.5%, a strong p-type doping effect is achieved in germanene/TCNQ. In particular, with increasing tensile strain over the range 2.5%–3%, the strain-tunable p-type doping effect decreases gradually. Such a multiple effect of molecular adsorption and strain on the electronic properties of germanane could be helpful for potential future applications of germanane-based electron devices.

DFT study including NBO, NLO response and reactivity descriptor of bis and tris (1,3-dithiole) tetrathiafulvalene

We present a density functional theory (DFT) study on the reactivity of bis and tris (1,3-dithiole) TTF 1-4 by using B3LYP/6-31G (d,p) level. The possible electrophile and nucleophile attacking sites of the title compounds is identified using MEP surface plot study. Highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy gaps were calculated to explain the frontier molecular orbitals and to predict the quantum chemical descriptors. Local reactivity properties have been investigated using average local ionization energies and Fukui functions. Natural Bond Orbital analysis was computed and possible transitions were correlated with the electronic transitions. The calculated first hyperpolarizability (β 0 ) of bis and tris (1,3-dithiole) TTF molecules, indicates that investigated molecules might have not the NLO applications. Keywords: tetrathiafulvalenes; density functional theory; computational chemistry; quantum chemical calculations.

Anderson-Type Polyoxometalates Functionalized by Tetrathiafulvalene Groups: Synthesis, Electrochemical Studies, and NLO Properties.

Three polyoxometalates (POMs) functionalized by tetrathiafulvalene (TTF) molecules have been synthesized by a coupling reaction between the Anderson-type POMs [MnMo6O18{(OCH2)3CNH2}2]3- or [AlMo6O18(OH)3{(OCH2)3CNH2}]3- and the TTF carboxylic acid derivative (MeS)3TTF(S-CH2-CO2H). The monofunctionalized TTF-AlMo6 POM contains one TTF group covalently grafted on an Al Anderson platform. The symmetrical TTF-MnMo6-TTF POM possesses two TTF groups grafted on each side of a Mn Anderson derivative while the asymmetrical TTF-MnMo6-SP POM contains a TTF and a spiropyran groups. These three trianionic species have been characterized by elemental analysis, 1H and 13C NMR, FT-IR spectroscopy, ESI-MS spectrometry, and single-crystal X-ray diffraction (for TTF-MnMo6-TTF). In the solid state, the grafted TTF molecules of TTF-MnMo6-TTF POMs interact via S···S and π···π interactions and form chains. The electrochemical properties of the complexes reflect the contributions of both the inorganic POM and the TTF moieties. Despite adsorption of the oxidized hybrid species on the Pt grid working electrode, UV-vis-NIR spectroelectrochemical investigations evidence peaks characteristic of the oxidation of the TTF units. Finally, hyper-Rayleigh scattering (HRS) measurements show that the three novel TTF derivatives exhibit β values between 20 and 37 × 10-30 esu. Moreover it is observed that the oxidation of the TTF moieties by Fe3+ ions increases the NLO response. These values are in the order of magnitude of that found for the well-known 4-dimethylamino- N-methyl-4-stilbazolium (DAS+) cation (β = 60 × 10-30 esu).

Tetrathiafulvalene-Tetracyanoquinodimethane Charge-Transfer Complexes Wired to Carbon Surfaces: Tuning of the Degree of Charge Transfer

Charge-transfer complexes involving tetrathiafulvalene (TTF) and tetracyanoquinodimethane (TCNQ) derivatives are engineered in a 2D arrangement onto a carbon surface through the exposure of immobilized TTF units to TCNQ compounds. TTF molecules were immobilized as robust monolayers on carbon surfaces using the electrografting method followed by a click chemistry coupling. When the TTF monolayer is exposed to TCNQ, TCNQF2 (2,5-difluoro-TCNQ), and TCNQF4 (2,3,5,6-tetrafluoro-TCNQ), strong donor–acceptor complexes are formed onto the surface. A considerable decrease of the electrochemical response accompanies the formation of the charge-transfer complex. This observation is rationalized by the analysis of original crystal samples using an ultramicroelectrode cavity, confirming that charge-transfer complexes are electrochemically silent. A fine control of the degree of charge transfer with the judicious choice of different acceptors is evidenced through electrochemical and X-ray photoelectron spectroscopy (XP...

Structural, Magnetic and DFT studies on a Charge-Transfer Salt of a Tetrathiafulvalenepyridyl-(1,5-diisopropyl) verdazyl Diradical Cation.

A new tetrathiafulvalene (TTF) donor covalently appended with a 1,5-diisopropylverdazyl radical through a cross-conjugated pyridyl linker (3) has been prepared and characterised. Reaction of 3 with tetracyanoquinonedimethane (TCNQ) afforded the 2:1 charge-transfer complex (3)2 ⋅TCNQ (4), in which the IR and structural data are consistent with 0.25 e- charge transfer from the TTF donor (D) to the TCNQ acceptor (A). The TTF and TCNQ molecules adopt a mixed-stack D⋅⋅⋅D⋅⋅⋅A arrangement that does not facilitate conduction. A solution EPR spectrum of 4 comprises a broad featureless singlet, which is consistent with the presence of a TCNQ radical anion. Theoretical studies were performed to probe the exchange interactions within selected fragments of 4 with and without charge transfer. In the absence of charge transfer, DFT calculations reveal weak antiferromagnetic exchange between verdazyl radicals within the (3)2 monoradical unit. However, partial oxidation of the dimer (3)2 to the diradical cation leads to an S= ground state, in which the verdazyl radical spins are now aligned co-parallel as a consequence of antiferromagnetic exchange to the additional delocalised TTF-based spin containing unit. The magnetic properties of 4 are consistent with a net S= spin state per formula unit with dominant antiferromagnetic interactions between spin-bearing building blocks.

Modulation of Energy Transfer into Sequential Electron Transfer upon Axial Coordination of Tetrathiafulvalene in an Aluminum(III) Porphyrin-Free-Base Porphyrin Dyad.

Axially assembled aluminum(III) porphyrin based dyads and triads have been constructed to investigate the factors that govern the energy and electron transfer processes in a perpendicular direction to the porphyrin plane. In the aluminum(III) porphyrin-free-base porphyrin (AlPor-Ph-H2Por) dyad, the AlPor occupies the basal plane, while the free-base porphyrin (H2Por) with electron withdrawing groups resides in the axial position through a benzoate spacer. The NMR, UV-visible absorption, and steady-state fluorescence studies confirm that the coordination of pyridine appended tetrathiafulvalene (TTF) derivative (TTF-py or TTF-Ph-py) to the dyad in noncoordinating solvents afford vertically arranged supramolecular self-assembled triads (TTF-py→AlPor-Ph-H2Por and TTF-Ph-py→AlPor-Ph-H2Por). Time-resolved studies revealed that the AlPor in dyad and triads undergoes photoinduced energy and/or electron transfer processes. Interestingly, the energy and electron donating/accepting nature of AlPor can be modulated by changing the solvent polarity or by stimulating a new competing process using a TTF molecule. In modest polar solvents (dichloromethane and o-dichlorobenzene), excitation of AlPor leads singlet-singlet energy transfer from the excited singlet state of AlPor ((1)AlPor*) to H2Por with a moderate rate constant (k(EnT)) of 1.78 × 10(8) s(-1). In contrast, excitation of AlPor in the triad results in ultrafast electron transfer from TTF to (1)AlPor* with a rate constant (k(ET)) of 8.33 × 10(9)-1.25 × 10(10) s(-1), which outcompetes the energy transfer from (1)AlPor* to H2Por and yields the primary radical pair TTF(+•)-AlPor(-•)-H2Por. A subsequent electron shift to H2Por generates a spatially well-separated TTF(+•)-AlPor-H2Por(-•) radical pair.

Random-walk annihilation process of photo-induced neutral-ionic domain walls in TTF-CA

The charge and lattice dynamics at the neutral-ionic phase transition in the organic mixed-stack compound TTF-CA were measured by time-resolved Fourier-transform infrared spectroscopy and modeled by Monte Carlo simulations on a one-dimensional chain. After photoexcitation in the ionic state, we observe transient changes in reflectivity, which follow a stretched-exponential behavior on a microsecond time scale. This implies that the dimerization between the TTF and CA molecules vanishes, creating metastable domains. The time, temperature and intensity dependences can be modeled by a diffusion-annihilation process of neutral-ionic domain walls. Their random walk explains the relaxation process and its characteristic decay with time.