Extensive Charge Transfer Research Articles

Theoretical insights into the structural, electronic and gas-sensing properties of Sc-decorated black phosphorus via strain engineering

Structural and electronic properties of Sc-decorated black phosphorus (SP) and its gas sensing for NO molecule were investigated using density functional theory with the emphasis on the response to applied strain. It found that SP transformed into indirect bandgap semiconductor, and converted into a metal characteristic under strain. SP showed strong interaction with the NO with a high adsorption energy of −2.92 eV since the orbital hybridization and extensive charge transfer, and exhibited 3.3-fold sensitivity compared to black phosphorus, suggesting that SP was a potential NO sensor. Furthermore, strain engineering provided an effective route to facilitate the desorption of NO.

Enabling a compatible Li/garnet interface via a multifunctional additive of sulfur

An intimate Li/garnet interface with an extended charge transfer area is constructed for improving the electrochemical performance of garnet-type solid-state batteries.

A New Aggregation Induced Emission Active Halochromic White Light Emissive Molecule: Combined Experimental and Theoretical Study

Red/near infrared-emissive organic molecules that are aggregation induced emission (AIE) active and having a pH-sensitive core are high in-demand for real-world applications. We have designed and synthesized a far-red to near infrared (NIR) fluorogenic donor–acceptor (D–A) type probe 4-((4-(2-(3,3-dimethyl-3H-indole-2-yl)vinyl)phenyl)(phenyl)amino)benzaldehyde (TPA-SCY), that can undergo protonation with a stronger intramolecular charge transfer. The molecule is pH-sensitive and responds to the acidic behavior of chloroform to produce a unique halochromic white-light emission. Owing to its sensitivity toward pH and its highly emissive nature in the red/NIR region at low pH (approximately 3–5), it accumulates in the intracellular lysosomes and can be used as a live-tracker for lysosomes. Successful application of time-dependent density functional theory with the use of an optimally tuned range-separated hybrid functional reproduces the experimental absorption and emission spectra within the 1–5 nm range (which is not observed when conventional range-separated hybrid functionals are used). Thus, the present work embodies synthesis and photophysical studies (supported by an efficient and highly accurate theoretical tool) of a new AIE active halochromic white light emissive molecule with extensive charge transfer properties and having the ability to behave as a live LysoTracker.

Fluorescent vinyl and styryl coumarins: A comprehensive DFT study of structural, electronic and NLO properties

Nonlinear optical properties of 3-styryl and 3-vinyl coumarin dyes have been investigated with Density Functional Theory (DFT) using global hybrid (GH) and range-separated hybrid (RSH) functionals. The performance of GHs - B3LYP, BHHLYP, PBE0, M06, M06L, M062X, and M06HF and RSHs - CAM-B3LYP, HISSbPBE, HSEH1PBE, wB97, wB97X, and wB97XD in combination with 6-311++G(d,p) basis set has been analyzed. Estimated (hyper) polarizability ( $$\alpha _{0}, \beta _{0})$$ obtained from the GHs - M06, M062X and PBE0 are in agreement with each other. The RSHs - wB97 and wB97X estimate very close values of $$\beta _{0}$$ . The $$\beta _{0}$$ value of 3-styryl and 3-vinyl coumarins reaches the maximum as the bond length alternation and bond order alternation parameters tend to zero. Natural bond orbital analysis shows there is extensive charge transfer in the excited state leading to large value of $$\beta _{0}$$ . The vibrational contribution to $$\alpha _{0}$$ and $$\beta _{0}$$ is significantly less when the donor is methoxy group and acceptor is nitro group in the 3-styryl coumarin. The dye, (E)-7-(diethylamino)-3-(4-nitrostyryl)-2H-chromen-2-one (3c) is found to give the highest NLO response. An increasing electrophilicity originating from the decreased HOMO-LUMO band gap leads to an increase in $$\alpha _{0} $$ and $$\beta _{0}$$ in all the cases. JCSC-D-17-00839R1 Synopsis - The NLO properties of 3-styryl and 3-vinyl coumarin dyes have been investigated thoroughly with the help of DFT using global hybrid (GH) and range-separated hybrid (RSH) functionals. The performance of GHs and RSHs in combination with 6-311++G(d,p) basis set has been analyzed. Calculated BLA/BOA index, NBO analysis, electrophilicity index and HOMO-LUMO gap are good agreement with the $$\alpha _{0}$$ and $$\beta _{0}$$ .

Strong Color Tuning of Self‐Assembled Azo‐Derived Phosphonic Acids upon Hydrogen Bonding

AbstractThe unexplored combination of a hydroxy‐gem‐bisphosphonic (HBP) unit with strongly absorbing azo dyes leads to the formation of a glassy material with unusual black color. Strong intermolecular hydrogen‐bonding interactions combined with extensive charge transfer are proposed from spectroscopic and mass spectrometry analyses performed in solution and on thin films. Dramatic color switch from blue gray/green to orange is obtained by varying the hydrogen‐bonding acceptor character of the solvent or substrate, thereby paving the way to tunable colored materials using HBP‐functionalized π‐conjugated molecules.

ChemInform Abstract: Ground- and Excited-State Dipole Moments of Some Nitroaromatics: Evidence for Extensive Charge Transfer in Twisted Nitrobenzene Systems

Electro‐optical absorption measurements have been made on four model nitroaromatics to determine the effect of twisting of the donor–acceptor single bond on the charge‐transfer characteristics in the Franck–Condon excited states. Observed ground‐ and excited‐state dipole moments of nitromesitylene, which has been treated experimentally as the nonplanar analogue of planar nitrobenzene, indicate that electronic excitation of twisted nitrobenzene results in a nearly full unit charge transfer from donor (benzene) to the acceptor (nitro) group (Δμ=18.3 D). On the other hand, in planar nitrobenzene and nitronaphthalene the charge transfer is more delocalized over the whole molecular skeleton, resulting in normal changes in dipole moment (Δμ=5–10 D). In the analogous anthracene system, i.e., 9‐nitroanthracene, the charge transfer upon electronic excitation is extremely low (Δμ=1.7 D), which is reflected by its very small change in the dipole moment. Therefore, it is evident that the charge‐transfer processes in the twisted molecules are quite different for different aromatic ring systems. Simple molecular‐orbital calculations satisfactorily explain the reason for such differences on the basis of their highest occupied molecular‐orbital (HOMO) and lowest unoccupied molecular‐orbital (LUMO) characteristics. Transition moment directions have also been obtained experimentally and compared with the theoretically predicted directions based on the symmetry properties of the HOMO and LUMO. Agreement is found in all cases studied.

X-ray Absorption Edge Spectroscopy and Computational Studies on LCuO2 Species: Superoxide−CuII versus Peroxide−CuIII Bonding

The geometric and electronic structures of two mononuclear CuO2 complexes, [Cu(O2){HB(3-Ad-5-(i)Prpz)3}] (1) and [Cu(O2)(beta-diketiminate)] (2), have been evaluated using Cu K- and L-edge X-ray absorption spectroscopy (XAS) studies in combination with valence bond configuration interaction (VBCI) simulations and spin-unrestricted broken symmetry density functional theory (DFT) calculations. Cu K- and L-edge XAS data indicate the Cu(II) and Cu(III) nature of 1 and 2, respectively. The total integrated intensity under the L-edges shows that the 's in 1 and 2 contain 20% and 28% Cu character, respectively, indicative of very covalent ground states in both complexes, although more so in 1. Two-state VBCI simulations also indicate that the ground state in 2 has more Cu (/3d8) character. DFT calculations show that the in both complexes is dominated by O2(n-) character, although the O2(n-) character is higher in 1. It is shown that the ligand L plays an important role in modulating Cu-O2 bonding in these LCuO2 systems and tunes the ground states of 1 and 2 to have dominant Cu(II)-superoxide-like and Cu(III)-peroxide-like character, respectively. The contributions of ligand field (LF) and the charge on the absorbing atom in the molecule (Q(mol)M) to L- and K-edge energy shifts are evaluated using DFT and time-dependent DFT calculations. It is found that LF makes a dominant contribution to the edge energy shift, while the effect of Q(mol)M is minor. The charge on the Cu in the Cu(III) complex is found to be similar to that in Cu(II) complexes, which indicates a much stronger interaction with the ligand, leading to extensive charge transfer.

Influence of solvent viscosity and permittivity on the dynamics of large amplitude motions in semiflexibly bridged electron donor–acceptor systemsDedicated to Professor F. Dörr on the occasion of his 80th birthday.

In electron donor–acceptor systems containing a nonrigid bridge, geometrical relaxations can occur after photoinduced charge separation under the influence of attractive Coulomb forces (harpooning mechanism). The investigated systems contained an aniline moiety as donor and a substituted naphthalene as acceptor, either one or both being substituted with large aliphatic wings. Two different types of large amplitude motions were identified: a rotation around a single bond leading from the fully extended charge transfer (ECT) conformer to an intermediate charge transfer (ICT) conformer, and the folding of the bridging piperidyl ring forming a compact charge transfer (CCT) state. To elucidate the effects of solvent viscosity and permittivity on these two relaxation processes, the time profiles of the fluorescence from the CCT state were recorded as functions of temperature (283<T/K<323) and pressure (0.1<p/MPa<320). The reaction constants for both relaxation processes were analysed assuming the functional form: k = Cη−a exp[ − ΔGEX‡(er)/RT]. It was found that the exponent a ranges between 0.75 and 0.85. In contrast to estimates for the gas phase, the deduced Gibbs activation energies ΔGEX‡(er) range between 8 and 15 kJ mol−1 for single bond rotation and between 10 and 18 kJ mol−1 for folding of the piperidyl ring. The results confirm the expectation that consideration of permittivity effects is crucial for an adequate interpretation when educt and transition state exhibit different dipole moments.

Conformational Dynamics of Charge-Transfer States in Donor−Bridge−Acceptor Systems

Donor−acceptor compounds containing a phenylenediamine electron donor and a naphthalene, a cyanobenzene, or a cyanonaphthalene acceptor were studied. The two chromophores are connected by three different bridging units, consisting of CH2 groups linked to a semiflexible piperidine or piperazine ring or to a rigid 2,5-diazabicyclo[2.2.1]heptane group. All donor−acceptor compounds show photoinduced charge separation, resulting in the formation of a compact charge-transfer (CCT) state in nonpolar solvents. The conformational change needed to arrive at this species is impossible in a nonpolar polymer matrix and also in methylcyclohexane at low temperature. In the cases of the piperidine- and piperazine-bridged donor−acceptor compounds, evidence for the involvement of an extended charge-transfer (ECT) species as a precursor of the CCT species was obtained from time-resolved fluorescence measurements. In contrast to harpooning systems studied previously, the energy differences between the species in the present case are so small that their interconversions are reversible within the excited state lifetimes.

Conformational dynamics of semiflexibly bridged electron donor–acceptor systems comprising long aliphatic tails

In continuation of our previous work on the conformational dynamics (harpooning mechanism) of semiflexibly bridged electron donor–acceptor systems we have studied a derivative with two long aliphatic chains tethered to the donor and acceptor moieties, respectively. The fitting of the time- and wavelength-resolved fluorescence curves required three components whose lifetimes varied smoothly with pressure (solvent viscosity). It is concluded that these three components correspond to three distinct conformations of the charge transfer state. Consequently, the previously established reaction scheme must be expanded by introducing an additional conformer termed the intermediate charge transfer (ICT) state, which differs from the previously defined extended charge transfer (ECT) state by rotation around the single bond connecting the acceptor to the bridge. Due to the enlarged hydrodynamic volume, this rotation is slowed down sufficiently to be easily detectable (1.7 × 108⩽krot/s−1⩽16 × 108). The rate of the folding process of the bridge leading from the ICT to the compact (CCT) conformational state is also reduced by a factor of 5 compared to the parent compound (5 × 107⩽kfold/s−1⩽40 × 107).

Conformational Dynamics of Semiflexibly Bridged Donor−Acceptor Systems Studied with a Streak Camera and Spectrotemporal Parametrization of Fluorescence

The fluorescence of four semiflexibly bridged donor−bridge−acceptor systems was studied with a streak camera system. The information-rich streak data make a detailed analysis possible of both the kinetics and the spectral changes that take place. From the analysis, it follows that all compounds studied undergo a photoinduced harpooning process in which long-range electron transfer creates an extended charge-transfer (ECT) species, which converts to a compact charge-transfer (CCT) species due to Coulombic attraction. Both the ECT and CCT species display CT fluorescence. The harpooning process occurs even in solvents of medium polarity (e.g., diethyl ether), whereas it has previously been assumed for related compounds that this process only occurs in the gas phase and in nonpolar alkane solvents.

Exploring the Limits of the Electrostatically Induced Conformational Folding Process in Charge-Separated Excited States: Retarding Effect of Long Alkyl Tails Attached to the Chromophores

Six new donor-bridge-acceptor compounds have been synthesized which contain a long n-tetradecyl chain attached to the donor or acceptor moiety, or to both of them. Systems 1, 2, and 3 are analogs of the fluorescent probe molecule Fluoroprobe (4). They contain a rigidly extended 4-methylenepiperidine bridge and show relatively strong charge transfer fluorescence in solvents of low and medium polarity. Systems 1a, 2a, and 3a contain a semiflexible 4-methylpiperidine bridge, obtained after hydrogenation of the exocyclic double bond of 1, 2 and 3, respectively. These systems undergo a conformational change following photoinduced charge separation (harpooning) in nonpolar solvents and probably also in solvents of medium polarity. Both the steady state fluorescence spectra and the fluorescence decay times of the extended charge transfer (ECT) species show that the photoinduced folding process is effectively slowed down by the introduction of the long alkyl tails. This is most pronounced for 1a which has an n-tetradecyl group attached to both donor and acceptor. In solution a small difference in the rate of folding is observed between 2a and 3a, which have a single n-tetradecyl chain attached to the acceptor only and to the donor only, respectively.

FTIR study of the photoinduced dissociation of CO2 on titania-supported noble metals

The effect of illumination on the activation and dissociation of CO2 was investigated at 190 and 300 K on titania-supported noble metals by means of Fourier transform infrared spectroscopy. The photoinduced dissociation of CO2 (through the formation of \(CO_{2(a)}^ - )\) resulting in CO(a) occurred on Pt/TiO2, Rh/TiO2 and Ir/TiO2; no CO(a) formation, however, was observed on Pd/TiO2 and Ru/TiO2. It is assumed that the CO2 on supported noble metals is bonded to the surface with both C (linked to a noble metal atom) and one of the O atoms (linked to the oxygen vacancy of the supports), and an extended charge transfer induced by illumination leads to the cleavage of a C–O bond.

Electric field induced second harmonic generation/third harmonic generation measurements on molecules with extended charge transfer: Absorption domain and strong resonance effects

An enlarged method of performing electric field induced second harmonic generation (EFISHG) or third harmonic generation (THG) measurements of molecular hyperpolarizabilities in the strongly resonant regime is proposed. The influence of absorption coefficients and anomalous dispersion are discussed in detail and corrections proposed which require no change in the experimental setup. An alternative method of data interpretation is presented and its validity discussed for two examples of molecular structures.

Infrared Spectroscopic Study of the Photoinduced Activation of CO2 on TiO2 and Rh/TiO2 Catalysts

The effect of illumination on the activation of CO[sub 2] was investigated at 190 K on oxidized, evacuated, and reduced TiO[sub 2] and Rh/TiO[sub 2] by means of Fourier transform infrared spectroscopy. The main effect observed for pure titania was an enhancement of the intensity of bands at 1640 and 1219 cm[sup [minus]1] due to bent CO[sub 2]. On Rh/TiO[sub 2] the photoinduced dissociation of CO[sub 2] also occurred, as indicated by the development of CO bands at 2020-2040 cm[sup [minus]1]. It is assumed that the CO[sub 2] on Rh/TiO[sub 2] is bonded to the surface with both C (linked to a Rh atoms) and one of the O atoms (linked to the oxygen vacancy of titania), and an extended charge transfer induced by illumination leads to the cleavage of a C-O bond. 44 refs., 5 figs., 1 tab.

Superfulleride formation and electronic properties of C60 on K/Rh(111) surfaces

Despite the high electron affinity of C60, photoemission and work function measurements of C60 on Rh(111) surfaces containing submonolayer amounts of K show that a low value of the work function is not sufficient to cause extensive charge transfer (> 1 electron) from the substrate to the C60 molecule. However, when appropriate amounts of C60 are evaporated onto potassium multilayers of controlled thickness at 100 K, interdiffusion occurs and potassium superfullerides, KxC60 with 6 <x < 12, form on the surface. The resulting phases can be purified by annealing the sample to ≈ 325 K for x → 12, or higher temperatures for lower K stoichiometries, to drive out excess K.

Coverage dependent adsorption sites in the K/Cu(100) system: A crystal truncation rod analysis

Abstract The analysis of the intensity along the diffraction rods normal to the crystal surface (crystal truncation rods) has been used to analyse the adsorption sites of potassium atoms adsorbed at T = 330 K on atomically clean Cu(100) under ultra high vacuum conditions. At potassium coverages below about Θ = 0.18 ML (1 ML = 1.53 × 1015 atoms cm−2), where no ordered adsorbate superstructure forms, the potassium atoms are adsorbed in the fourfold hollow sites of the Cu(100) substrate at d 1 = 2.1(4) Å above the first Cu layer corresponding to an effective potassium radius of r eff = 1.5(3) Å which is close to the ionic radius of 1.33 Å. Within about 1 –2% the substrate interlayer spacings, d 12 and d 23 are not affected. At high coverage (Θ ≈ 0.30 ML) where an ordered incommensurate overlayer forms, the adsorption site is partially on-top. These results are in correspondence with the model of alkalimetal adsorption on metals supposing extensive charge transfer from potassium to the substrate at low coverage.

Adsorption of hydrogen and deuterium on potassium-promoted Pd(100) surfaces

The adsorption of H 2 and D 2 has been studied on clean and K-promoted Pd(100) surfaces using thermal desorption, work function changes, ultraviolet photoelectron and Auger spectroscopy. The potassium adlayer significantly lowers the sticking coefficient (from 0.6 to 0.06 at θ k = 0.2), and the uptake of hydrogen, but increases the desorption energy for H 2 desorption. Calculation showed that each potassium adatom blocks approximately 4–5 adsorption sites for H 2 adsorption. Atomization of hydrogen led to an increase of hydrogen uptake. The adsorption of potassium on the H-covered surface caused a significant decrease in the amount of hydrogen adsorbed on the surface (as indicated by less desorbing hydrogen below 500 K) and promoted the dissolution of H atoms into the bulk of Pd. The dissolved hydrogen was released only above 600–650 K. In the interpetation of the results the extended charge transfer from K-dosed Pd to the adsorbed H atoms and the direct interaction between adsorbed H and K adatoms are taken into account.

Ground- and excited-state dipole moments of some nitroaromatics: Evidence for extensive charge transfer in twisted nitrobenzene systems

Electro-optical absorption measurements have been made on four model nitroaromatics to determine the effect of twisting of the donor–acceptor single bond on the charge-transfer characteristics in the Franck–Condon excited states. Observed ground- and excited-state dipole moments of nitromesitylene, which has been treated experimentally as the nonplanar analogue of planar nitrobenzene, indicate that electronic excitation of twisted nitrobenzene results in a nearly full unit charge transfer from donor (benzene) to the acceptor (nitro) group (Δμ=18.3 D). On the other hand, in planar nitrobenzene and nitronaphthalene the charge transfer is more delocalized over the whole molecular skeleton, resulting in normal changes in dipole moment (Δμ=5–10 D). In the analogous anthracene system, i.e., 9-nitroanthracene, the charge transfer upon electronic excitation is extremely low (Δμ=1.7 D), which is reflected by its very small change in the dipole moment. Therefore, it is evident that the charge-transfer processes in the twisted molecules are quite different for different aromatic ring systems. Simple molecular-orbital calculations satisfactorily explain the reason for such differences on the basis of their highest occupied molecular-orbital (HOMO) and lowest unoccupied molecular-orbital (LUMO) characteristics. Transition moment directions have also been obtained experimentally and compared with the theoretically predicted directions based on the symmetry properties of the HOMO and LUMO. Agreement is found in all cases studied.

X-ray photoelectron spectroscopy studies of some chemically prepared polypyrrole-halobenzoquinone complexes

X-ray photoelectron spectroscopy (XPS) studies were performed on conductive polypyrrole-tetrafluoro-p-benzoquinone (PPY-p-fluoranil), polypyrrole-tetrachloro-p-benzoquinone (PPY-p-chloranil) and polypyrrole-tstrabromo-o-benzoquinone (PPY-o-bromanil) complexes prepared via the simultaneous chemical polymerization and oxidation of pyrrole by the respective acceptor. In all complexes, XPS data suggested the presence of negatively charged oxygen, the halogen anion and the positively charged pyrrolylium nitrogen. More extensive charge transfer interaction in the complexes is associated with higher electrical conductivity. However, the charge transfer interactions in each complex may have proceeded further than the pure formation of molecular complex.