Time-dependent Density Functional Theory Research Articles

Spectroscopic Signature of Metal-hydroxo and Peroxo Species in K-edge X-ray Absorption Spectra.

Metal-dioxygen species are important intermediates formed during dioxygen activations by metalloenzymes in various biological processes, by catalysts in fuel cells, and prior to O2 evolution by photosystem II. In this work, we focus on manganese-porphyrin complexes using tetramesitylporphyrin ligand (TMP) to explore changes in Mn K-edge X-ray absorption spectroscopy (XAS) associated with the formation of Mn-hydroxide and Mn-O2 peroxide species. With limited spectroscopic characterization of these compounds, Mn Kβ X-ray emission spectroscopy (XES), XAS, density functional theory (DFT), and time-dependent DFT (TD-DFT) analysis will enhance our understanding of their complex electronic structure. We show that the shape of the pre-edge in the K-edge Mn X-ray absorption near-edge structure (XANES) can serve as a spectroscopic signature of the MnIII-peroxo formation and thus can be used to track the presence of the side-on peroxide as an intermediate in time-resolved or in situ experiments. Our results will help to further summarize the spectroscopic fingerprints for peroxo and hydroxo species, addressing the challenge of identifying the reactive metal species in catalytic reactions.

Computational chemistry facilitates the development of second near-infrared xanthene-based dyes.

The dyes in the second near-infrared (NIR-II) region play a crucial role in advancing imaging technology. However, developing small-molecule dyes in NIR-II poses a significant bottleneck to meet the substantial demands in biological fields, which may be attributed to the lack of a rational design strategy. Herein, we designed a series of rhodamine analogs with more red-shifted emission by replacing the oxygen-bridge atom in xanthene-based dyes with -C(CH3)2, -Si(CH3)2, -SO2, and -P(O)Ph. We investigated the frontier molecular orbital, electrostatic potential surfaces, the interaction region indicator, electron-hole distribution, and absorption and emission spectrum of xanthene-based dyes using (time-dependent) density functional theory. Our results demonstrated that these designed small molecular dyes exhibit long emission wavelengths covering 1377-1809nm. We expected these findings to enable the targeted design of long-wavelength rhodamines. Geometry optimization of dyes in the ground and excited states was carried out at ω-B97XD/Def2SVP level using Gaussian 16 A03. The absorption and emission wavelengths were evaluated using 13 functional, including TPSSH, O3LYP, B3LYP*, B3LYP, PBE0, MPW1B95, PBE-1/3, PBE38, MPWB1K, MN15, BHandHLYP, ω-B97XD, and CAM-B3LYP.

Theoretical investigation on the surrounding effects of second-order nonlinear properties for (N^C^N)Pt(II)Cl complexes

Pt(II) complexes are widely used as nonlinear optical (NLO) materials. The geometric and electronic structures, second-order NLO property and UV–Vis absorption spectra of (N^C^N)Pt(II)Cl complexes (1–4) N^C^N binding by central benzene and two lateral N-heterocycles) are evaluated by density functional theory (DFT) and time-dependent DFT calculations. The detailed environmental effect of total first hyperpolarizability (βtot) in the solution and crystal phases is simulated by polarized continuum model (PCM) and quantum mechanics/molecular mechanics (QM/MM) method, respectively. The results highlight that the complex 3 exhibits largest βtot value in the gas, solution and crystal phases which can be attributed to the higher electron π-delocalization of ligands. Further, an evident red shift towards longer wavelength is observed for the complex 3. The origin of larger βtot value can be reasonably interpreted by the two-level model. In addition, the surrounding exerts an important influence on modulating second-order NLO properties. The solvent effect results in the larger βtot value than that of gas phase. The intermolecular interaction plays an important role in crystal phase. The formation of dimer can reduce the βtot value in comparison with the βtot value of the monomer in the crystal phase, because the centrosymmetric configuration of dimer implies a decrease of dipole moment (μ) in contrast to the large μ value of monomer. It is expected that this work will provide some guidance for designing Pt(II) NLO materials.

Quantum Chemical Analysis of the Molecular and Fragment Ion Formation of Butyrophenone by High-Electric Field Tunnel Ionization at Atmospheric Pressure.

The molecular ion M+· was observed when the liquid sample of butyrophenone was supplied using atmospheric pressure corona discharge (APCD). In contrast, the vapor supply resulted in the formation of the protonated molecule [M+H]+. The mass spectrum obtained with the liquid supply showed two distinctive fragment ions at m/z 105 and 120, resulting from α-cleavage and McLafferty rearrangement (McLR), respectively. The APCD spectrum showed peaks of M+· and the characteristic two fragment ions that were the same as the field ionization mass spectra of butyrophenone as reported by Chait et al. and Beckey et al. The formation of the molecular and fragment ions strongly indicated that high-electric field tunnel ionization (HEFTI) occurs by the HEF strength exceeding 108 V/m at the tip of the corona needle in APCD. The charge and spin density distributions of the molecular and fragment ions were analyzed by quantum chemical calculations using time-dependent density functional theory (TDDFT) and natural bond orbital (NBO) analysis.

Influence of Plasmonic Au@Cl/N Co‐doped Carbon Dots on the Performance of Dye‐Sensitized Solar Cells

ABSTRACTThe synergistic influence of the LSPR (localized surface plasmon resonance) of gold nanoparticles (Au NPs) and the effect of nitrogen and chlorine co‐doped carbon dots (Cl/N‐CQDs) on dye‐sensitized solar cells (DSSCs) performance are investigated. The gold NPs are coated with a thin layer of Cl/N‐CQDs to produce the Au@Cl/N‐CQDs structure. DSSCs are fabricated by using Au@Cl/N‐CQDs as co‐sensitizer. The focus of this work is to examine the effects of plasmonic Au NPs and carbon dots in addition to their synergistic effect by capping the Au NPs with Cl/N‐CQDs, and track their influence in DSSCs. N719 as ruthenium‐based dye, and natural dyes including betanin, crocin, carthamin, curcumin, chlorophyll, mallow, and lawsone are selected and applied in the DSSCs co‐sensitized by Au@Cl/N‐CQDs. The power conversion efficiency (PCE) of DSSCs using all of the selected dyes is enhanced upon using the Au@Cl/N‐CQDs. It is due to the improvement in VOC (open circuit voltage) and JSC (short circuit photocurrent densities) relative to the use of dyes alone. Based on computational results, Au@Cl/N‐CQDs cause a red‐shift in comparison with pure dyes. The TD‐DFT (time‐dependent density functional theory) results show that the orbitals from the Au@Cl/N‐CQDs in dye/Au@Cl/N‐CQDs have contribution in most of the absorptions. In other words, electrons from HOMO (highest occupied molecular orbital) of Au@Cl/N‐CQDs is transferred to the LUMO (lowest unoccupied molecular orbital) of dye, in most cases.

Optical spectra of silver clusters and nanoparticles from 4 to 923 atoms from the TDDFT+U method

The localized surface-plasmon resonances of coinage-metal clusters and nanoparticles enable many applications, the conception and necessary optimization of which require precise theoretical description and understanding. However, for the size range from few-atom clusters through nanoparticles of a few nanometers, where quantum effects and atomistic structure play a significant role, none of the methods employed previously has been able to provide high-quality spectra for all sizes. The main problem is the description of the filled shells of d electrons which influence the optical response decisively. We show that the DFT+U method, employed with real-time time-dependent density-functional theory calculations (RT-TDDFT), provides spectra in good agreement with experiment for silver clusters ranging from 4 to 923 atoms, the latter representing a nanoparticle of 3 nm. Both the electron-hole-type discrete spectra of the smallest clusters and the broad plasmon resonances of the larger sizes are obtained. All calculations use the value of the effective U parameter that provides good results in bulk silver. The agreement with experiment for all sizes shows that the U parameter is surprisingly transferable. Our results open the pathway for calculations of many practically relevant systems including clusters coupled to bio-molecules or to other nano-objects.

Experimental and computational analysis of poly(4-vinyl pyridine) and polyvinylpyrrolidone as effective corrosion inhibitors for low carbon steel in sulfuric acid

This study investigates the inhibitory effects of poly(4-vinyl pyridine) (P4VP) and polyvinylpyrrolidone (PVP) on the corrosion of low carbon steel (LCSt) in 1 M H2SO4. Protection efficacy (%PE) was measured using mass loss, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). Results showed %PE values increased with higher polymer concentration and lower temperature. At 450 mg/L, %PE reached 93.13% and 94.19% for P4VP and PVP, respectively. These polymers function as mixed inhibitors, adsorbing onto the LCSt surface per Langmuir’s model as a mode of physical adsorption. EIS indicated that higher polymer concentration increased charge transfer resistance and decreased effective double-layer capacitance. Both P4VP and PVP also reduced pitting corrosion in chloride-containing solutions. Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) optimized the molecular structures of the inhibitors, evaluating electronic parameters such as frontier molecular orbital (FMO) energies, energy gap, softness, hardness, electron transfer fraction, dipole moment, and hyperpolarizability ( β ° ). Monte Carlo (MC) and molecular dynamics (MD) simulations provided insights into adsorption mechanisms, corroborating experimental findings and highlighting the effect of protonation. This comprehensive study enhances our understanding of the relationship between molecular structure and function in polymer inhibitors, improving their application in corrosion protection.

Investigation of H-Bonding and pH on the Fluorescence Spectral Behavior of Valsartan.

The photophysical properties of valsartan (VAL), a potent phenyl tetrazole derivative sartan, were investigated. Valsartan has absorption bands at 230nm and 255nm and a fluorescence band at about [Formula: see text] = 346nm in butanol which is red shifted depending on the H-bonding capability of the solvent. The role of H-bonding in the excited state was approved through the linear correlation of the emission energy of VAL with Camlet-Taft acidity and basicity parameters, α and β, of polar protic solvents. The position and intensity of fluorescence emission bands of VAL are found to be pH dependent, shifting from 425nm at pH 2 to 375nm at pH 4 with enhancement of intermolecular H-bonding and fluorescence intensity depletion beyond pH 5 with formation of tetrazole anion. The results were supported by time-resolved fluorescence measurements which indicated the presence of different species with different lifetimes in the excited state depending on solution pH value. Computational results based on time dependent density functional methods (TDDFT) show that the tetrazole moiety is involved in the [Formula: see text] absorption transitions, while natural bond analysis (NBO) shows that VAL adopts a dimer conformation in water because of effective intermolecular H-bonding.

When a Twist Makes a Difference: Exploring PCET and ESIPT on a Nonplanar Hydrogen-Bonded Donor-Acceptor System.

Bioinspired benzimidazole-phenol constructs with an intramolecular hydrogen bond connecting the phenol and the benzimidazole have been synthesized to study both proton-coupled electron transfer (PCET) and excited-state intramolecular proton transfer (ESIPT) processes. Strategic incorporation of a methyl group disrupts the coplanarity between the aromatic units, causing a pronounced twist, weakening the intramolecular hydrogen bond, decreasing the phenol redox potential, reducing the chemical reversibility, and quenching the fluorescence emission. Infrared spectroelectrochemistry and transient absorption spectroscopy confirm the formation of the oxidized product upon PCET and probe excited-state relaxation mechanisms, respectively. Density functional theory calculations of redox potentials corroborate the experimental findings. Additionally, time-dependent density functional theory calculations uncover the fluorescence quenching mechanism, showing that the nonradiative twisted intramolecular charge transfer state responsible for fluorescence quenching is more energetically favorable in the methyl-substituted system. Incorporating groups causing steric hindrance expands the design of biomimetic systems capable of performing both PCET and ESIPT.

Vuv/vis absorption spectroscopy of different PAHs

AbstractThe present study provides new solid-phase absorption data of different Polycyclic Aromatic Hydrocarbon (PAHs) molecules in the Far Ultraviolet (FUV) and UV/Visible regions. Two features of interstellar extinction curves fall in this region: the FUV rise and the UV bump. Here, thin films of PAHs were prepared by means of the spin coating method onto a transparent substrate, and their solid phase absorption spectra were recorded. Spectra of isolated molecules simulated by Time-Dependent Density Functional Theory (TD-DFT) calculations were also produced for comparison. The results fit quite well with the FUV rise but not with the UV bump. Given the scarcity of FUV experimental absorption data of PAHs in the literature and especially in solid phase, these results are also interesting for reference for other studies ranging from thin films applications to interstellar medium models.

A Sodium Metal-Organic Framework with Deep Blue Room-Temperature Phosphorescence.

It is a great challenge to manufacture room-temperature blue long afterglow phosphorescent materials adapted to environmental conditions. Herein, an Na-based metal-organic framework (MOF) was constructed using Na+ and 1H-1,2,4-triazole-3,5-dicarboxylic acid, which exhibits long-lived of 378.9 ms, deep blue and room-temperature phosphorescence, meanwhile possesses the visible blue afterglow for 3~6 seconds after removing excitation light source. The three-dimensional coordination bonds network provided by Na-based MOF protects the organic ligands intrinsic hydrogen bond network, resulting in the phosphor lifetime and residual color remaining unchanged in different gas atmospheres. Furthermore, first-principles time-dependent density functional theory reveals that the rigid Na-based MOF structure can limit the rotation and vibration of the room-temperature phosphorescent organic ligands. This limitation results in the suppression of non-radiative decay for both singlet and triplet excitons, promotes intersystem crossing, and increases the rate of radiative decay, ultimately achieving long-lived room-temperature phosphorescence.

Effects of functional groups on ESIPT and antioxidant activity of apigenin: A non-existent enol* state fluorescein

The development and enhancement of antioxidant drugs, which are aimed at mitigating DNA damage, mutations, and cancer, are of paramount significance in the biomedical sphere. In recent years, antioxidant drug molecules with photoluminescence have sprung up like mushrooms. Apigenin (AP), characterized by its distinctive property of excited state intramolecular proton transfer (ESIPT), plays a pivotal role in mediating antioxidant and anticancer activities. Despite being a representative molecule of the non-existent enol form (E*) state with ESIPT nature, there is a notable lack of theoretical investigations into its antioxidant properties. Herein, density functional theory (DFT) and time-dependent DFT methodologies were utilized to explore the effects of various functional groups on AP molecules in a methanol solvent. Studies have demonstrated that for the non-existent E* state fluorescence molecule AP, the ESIPT process can significantly enhance the antioxidant potency of AP and its derivatives. However, the introduction of electron-withdrawing groups significantly accelerated the ESIPT process while simultaneously suppressing the antioxidant activity of AP-CN. Conversely, the incorporation of electron-donating groups effectively inhibited the ESIPT process, yet markedly enhanced the antioxidant activity of AP-NH2. This investigation furnishes vital perspectives and sources of reference for the conception and advancement of groundbreaking antioxidant medications that aim to tackle non-existent E* state molecules.

A-Site Doping Promotes CO2 Activation and Prolongs Charge Carrier Lifetimes in SrTiO3: Insight from Quantum Dynamics.

Using time-dependent density functional theory and nonadiabatic molecular dynamics, we systematically investigated the effect of A-site doping on the CO2 activation and charge carrier lifetimes in SrTiO3(STO). Our simulations revealed that A-site doping significantly enhances the chemical adsorption of CO2 on SrTiO3 surfaces, which is beneficial for promoting CO2 activation. Moreover, we found that A-site doping can efficiently stabilize the lowest unoccupied molecular orbital (LUMO) of CO2 near the conduction band minimum of STO, promoting the photogenerated electron transfer from the conduction band of STO to the CO2 LUMO. Importantly, A-site doping causes a significant nonadiabatic coupling reduction and prolongs the charge recombination time by a factor of 1.86 compared to the pristine STO. Our study clarifies the influencing mechanism of A-site doping on CO2 activation and charge carrier lifetimes and suggests important principles for the design of high-performance photocatalytic semiconductors.

Study of the Energy Crossing Between Excited States Affected by the Electronegativity of Substituents for Three 4-Azido-1,8-naphthalimide Derivatives.

Rapid detection of H2S is crucial for human physiological health and natural ecosystems. In this study, the fluorescent sensing mechanisms of three 4-azido-1,8-naphthalimide-based fluorescent probes to monitor H2S were theoretically investigated by density functional theory and time-dependent density functional theory. The potential energy curve of the charge transfer (CT) state has a crossover with that of the locally excited (LE) state proved by the constructed linear interpolating internal coordinate pathway. Thus, the transform takes place from the LE state to the CT state causing the fluorescence quenching of the probes from a nonradiative transition process of the CT state. The distance between the Franck-Condon point and the minimal energy conical intersection becomes larger with the increase of the electronegativity of substituents on the 1,8-naphthalimide fluorophore. In addition, the degree of charge separation is closely related to the energy difference between the CT and the LE states which are also essentially affected by the electronegativity of the substituents. Since the electronegativity of the substituents has proved important for the probes, our work lays a certain theoretical foundation for the design and synthesis of more sensitive 4-azido-1,8-naphthalimide-based fluorescent probes.

Investigating the acceptor tuned effect on INPOD-based efficient D-π-A organic chromophores for optoelectronic utilization through quantum chemical analysis

In this study, the dye-sensitized solar cells and non-linear optical capabilities of newly designed ((E)-2-amino-5-((5-(4-p-tolyl-1,2,3,3a, 4,8 b-hexahydrocyclopenta [b]indol-7-yl)thiophen-2-yl)methylene)thiazol-4(5H)-one (INPOD)-based A1-A6 organic chromophores were examined. To create a D-π-A structure, the A1-A6 molecules were positioned on the electron donor, spacer, and acceptor, respectively. The use of hybrid functionals including PBEPBE, CAM-B3LYP, and MPW1PW91 was evaluated for the maximum absorption wavelength of INPOD. According to the calculated outcomes, MPW1PW91 exhibited λmax closest to INPOD. Consequently, the optical absorption spectra of A1-A6 were employed by this method to identify the key factors. The photovoltaic characteristics of these compounds in dye-sensitized solar cells were studied theoretically. The acceptor category affected the photovoltaic performance of A1-A6. Through the quantum chemical technique in time-dependent density functional theory methods, the electronic charge distribution and intramolecular charge transfer inside the A1-A6 were found. Time-dependent density functional theory calculations revealed that all A1-A6 had a λmax, that was greater than the INPOD (437 nm) in the range of 564–806 nm. A6 demonstrated an electron reorganization energy of 0.2340 eV, while a hole reorganization energy of 0.1006 eV. These values represent the maximum mobility of holes and electrons among all values. Additionally, the open circuit voltage was calculated after coupling each compound with a PTB7-Th. By the Voc of 2.10, 2.06, 2.22, and 2.08 eV, the A1, A3, A4, and A5 dyes produced the best results, respectively. The A1-A6 sensitizers were used to derive the non-linear optical properties of the dipole moment, polarizability, and first-order hyperpolarizability. It was noticed from the calculated results that the A2 and A6 molecules have the best options for non-linear optical activity. It tested how well the A1-A6 dyes performed in terms of charge transfer, dye regeneration, electron injection driving force, light harvesting efficiency, transition density matrix, molecular electro-potential, and density of states. The computed result showed that A2 and A6 chromophores are excellent candidates for dye-sensitized solar cells. Finally, those dye derivatives would certainly work effectively as tuning-A in optoelectronic applications.

Roles of ESIPT and TICT in the Photophysical Process of a Ratiometric Fluorescence Sensor for Al3.

Precise detection of Al3+ with the aid of a fluorescence sensor is of fundamental importance in the fields of water pollution control and food safety. A comprehensive understanding of the photophysical process of the sensor as well as its underlying detection mechanism is a precondition for the design of highly efficient sensors. This contribution performs a thorough investigation of the ratiometric fluorescence sensing mechanism of an Al3+ sensor with the aid of density functional theory and time-dependent density functional theory. Two excited-state intramolecular proton transfer (ESIPT) processes are observed on the S1 state potential energy surface, which leads to emission around 565 nm. A twisted intramolecular charge transfer state is observed after one of the ESIPT processes via cis-trans isomerization of the C═N bond. However, the large energy barrier hinders its occurrence, which is quite unusual. Al3+ is found to form three strong coordination bonds with the sensor, which eliminates ESIPT processes and induces a significant blue shift of the emission spectrum to 480 nm. The origination of the sensor's selectivity is also uncovered by investigating the interaction between the sensor and interfering metal ions.

DFT study of electronic and nonlinear optical properties of alkaline earth metals and superalkalis doped all-cis-1, 2, 3, 4, 5, 6-hexafluorocyclohexane as an efficient excess electron system

Continual advancements are being pursued to discover innovative strategies for developing materials with remarkable nonlinear optical (NLO) response. Herein, electronic, geometric, thermodynamic and NLO properties of excess electron systems based on stacked Janus dimer, all-cis-1,2,3,4,5,6-hexafluorocyclohexane (C6H6F6)2 are thoroughly investigated. The excess electron systems are designed by doping alkaline earth metals (AEMs) on fluorine face and superalkalis on hydrogen face of Janus dimer. The higher values of vertical ionization energies (VIE) and interaction energies (Eint), confirm the electronic and thermodynamic stabilities of the designed complexes, respectively. Natural bond orbital (NBO) analysis is performed, and the excess electron character of the complexes is confirmed through frontier molecular orbital (FMO) analysis by highest occupied molecular orbital (HOMO) iso-densities. FMO shows a significant decrease in energy gaps (Egap) of the complexes (i.e., Eg = 1.80–3.12 eV), compared to the stacked Janus dimer (i.e., Eg = 9.41 eV). The transparency of the complexes to UV region is confirmed through UV–vis analyses, revealing their maximum absorption in visible and near-IR regions. The higher NLO response of the designed excess electron systems is further proved by the greater values of first hyperpolarizability (β o ) i.e., up to 1.70 × 106 au. Moreover, the time dependent-density functional theory (TD-DFT) computations and two-level model are employed to investigate the controlling factors of hyperpolarizability, illustrating the contribution of transition energy (∆E3), change in dipole moment (∆μ) and oscillator strength (f o ) in controlling the β o . Ab-initio molecular dynamics (AIMD) simulation further confirm that the designed superalkalide complexes are kinetically and thermally stable. The thorough investigation of these excess electron systems proves them an appropriate candidate for NLO applications.

Theoretical Procedure for Precise Evaluation of Chemical Enhancement in Molecular Surface-Enhanced Raman Scattering.

The enhancement of the molecular Raman signal in plasmon-assisted surface-enhanced Raman scattering (SERS) results from electromagnetic and chemical mechanisms, the latter determined to a large extent by the chemical interaction between the molecules and the hosting plasmonic nanoparticles. A precise quantification of the chemical mechanism in SERS based on quantum chemistry calculations is often challenging due to the interplay between the chemical and electromagnetic effects. Based on an atomistic description of the SERS signal, which includes the effect of strong field inhomogeneities, we introduce a comprehensive approach to evaluate the chemical enhancement in SERS, which conveniently removes the electromagnetic contribution inherent to any quantum calculation of the Raman polarization. Our approach uses density functional theory (DFT) and time-dependent DFT to compute the total SERS signal, together with the electromagnetic and chemical enhancement factors. We apply this framework to study the chemical enhancement of biphenyl-4,4'-dithiol embedded between two gold clusters. Although we find that for small clusters the total SERS enhancement is mainly determined by the chemical mechanism, our procedure enables removal of the electromagnetic contribution and isolation of the contribution of the bare chemical effect. This approach can be applied to reproduce and understand Raman line activation and strength in practical and challenging SERS configurations such as in plasmonic nano- and pico-cavities.

Amplifying the photovoltaic properties of tetrathiafulvalenes based materials by incorporation of small acceptors: a density functional theory approach

Currently, polycyclic aromatic compounds in organic solar cells (OSCs) have gained substantial consideration in research communities due to their promising characteristics. Herein, polycyclic aromatic hydrocarbons (PAHs) core-based chromophores (TTFD1-TTFD6) were designed by structural modifications of peripheral acceptor groups into TTFR. The density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations were carried out at B3LYP/6-311G (d, p) functional to explore insights for their structural, electronic, and photonic characteristics. The structural modulation unveiled notable electronic impact on the HOMO and LUMO levels across all derivatives, leading to decreased band gaps. All the designed compounds exhibited band gap ranging from 2.246 to 1.957 eV, along with wide absorption spectra of 897.071-492.274 nm. An elevated exciton dissociation rate was observed due to the lower binding energy values (Eb = 0.381 to 0.365 eV) calculated in the derivatives compared to the reference (Eb = 0.394 eV). Furthermore, data from the transition density matrix (TDM) and density of states (DOS) also corroborated the effective charge transfer process. Comparable results of Voc for reference and designed chromophores were obtained via HOMOdonor−LUMOPC71BM. The declining Voc order values was noted as TTFD5 > TTFD6 > TTFD4 > TTFD3 > TTFD2 > TTFD1 > TTFR. Interestingly, TTFD5 was found with the smallest energy gap and highest absorption value, resulting in better charge transference among all the derivatives. The results illustrated that the modification in indenofluorene based chromophores with end-capped small acceptors proved to be a significant approach in achieving favorable photovoltaic properties.

TICT, and Deep-Blue Electroluminescence from Acceptor-Donor-Acceptor Molecules.

Donor-acceptor (D-A) materials based on butterfly-shaped molecules could inhibit exciton-migration-induced quenching due to molecular twist. To explore this attribute towards beneficial photophysical properties, three novel bipolar acceptor-donor-acceptor (A-D-A) molecules with triphenyl triazine end capping along with substitution ortho to the Tröger's base (TB) scaffold varying from H, Me, and F were explored. The installation of H/Me/F imparted an electron push-pull effect with concomitant maneuvering of photophysical properties. On increasing solvent polarity, a remarkable bathochromic shift with a significant decrease in emission efficiency was observed due to the twisted intramolecular charge transfer state (TICT). Emission enhancement in the ethylene glycol-water mixture and diminution in the THF-water mixture further confirmed the existence of TICT states in these TBs. The torsional dynamics in the excited state were also evidenced by the time-dependent density-functional theory (TD-DFT) calculations. Owing to the butterfly architecture of the TB that suppressed TICT, TB-Trzs exhibited a significant blue shift, accompanied by a favorable quantum yield in the solid state. Among the three compounds, Me-TB-Trz exhibited deep-blue photoluminescence and was explored as a dopant in organic light-emitting diodes (OLEDs) to obtain deep-blue electroluminescence of brightness 4128 cdm-2 and CIE coordinates of (0.16, 0.09).