Publications FRom UCR, UofR, and JNCASR

Multivalent batteries, such as magnesium-ion, calcium-ion, and zinc-ion batteries, have attracted significant attention as next-generation electrochemical energy storage devices to complement conventional lithium-ion batteries (LIBs). Among them, calcium-ion batteries (CIBs) are the least explored due to difficult reversible Ca deposition–dissolution. In this work, we examined the stability of four different Ca salts with weakly coordinating anions and three different solvents commonly employed in existing battery technologies to identify suitable candidates for CIBs. By employing Born–Oppenheimer molecular dynamics (BOMD) simulations on salt-Ca and solvent-Ca interfaces, we find that the tetraglyme solvent and carborane salt are promising candidates for CIBs. Due to the strong reducing nature of the calcium surface, the other salts and solvents readily decompose. We explain the microscopic mechanisms of salt/solvent decomposition on the Ca surface using time-dependent projected density of states, time-dependent charge-transfer plots, and climbing-image nudged elastic band calculations. Collectively, this work presents the first mechanistic assessment of the dynamical stability of candidate salts and solvents on a Ca surface using BOMD simulations, and provides a predictive path toward designing stable electrolytes for CIBs.

We apply direct nonadiabatic dynamics simulations to investigate photoinduced charge transfer reactions. Our approach is based on the mixed quantum-classical fewest switches surface hopping (FSSH) method that treats the transferring electron through time-dependent density functional theory and the nuclei classically. The photoinduced excited state is modeled as a transferring single-electron that initially occupies the LUMO of the donor molecule/moiety. This single-particle electronic wave function is then propagated quantum mechanically by solving the time-dependent Schrödinger equation in the basis of the instantaneous molecular orbitals (MOs) of the entire system. The nonadiabatic transitions among electronic states are modeled using the FSSH approach within the classical-path approximation. We apply this approach to simulate the photoinduced charge transfer dynamics in a few well-characterized molecular systems. Our results are in excellent agreement with both the experimental measurements and high-level (yet expensive) theoretical results.

The accurate prediction of band gaps and structural properties in periodic systems continues to be one of the central goals of electronic structure theory. However, band gaps obtained from popular exchange–correlation (XC) functionals (such as LDA and PBE) are severely underestimated partly due to the spurious self-interaction error (SIE) inherent to these functionals. In this work, we present a new formulation and implementation of Wannier function-derived Fermi–Löwdin (WFL) orbitals for correcting the SIE in periodic systems. Since our approach utilizes a variational minimization of the self-interaction energy with respect to the Wannier charge centers (WCC), it is computationally more efficient than the HSE hybrid functional and other self-interaction corrections that require a large number of transformation matrix elements. Calculations on several (17 in total) prototypical molecular solids, semiconductors, and wide-bandgap materials show that our WFL self-interaction correction approach gives better band gaps and bulk moduli compared to semilocal functionals, largely due to the partial removal of self-interaction errors.

By combining experimental measurements with ab initio molecular dynamics simulations, we provide the first microscopic description of the interaction between metal surfaces and a low-temperature nitrogen–hydrogen plasma. Our study focuses on the dissociation of hydrogen and nitrogen as the main activation route. We find that ammonia forms via an Eley–Rideal mechanism where atomic nitrogen abstracts hydrogen from the catalyst surface to form ammonia on an extremely short time scale (a few picoseconds). On copper, ammonia formation occurs via the interaction between plasma-produced atomic nitrogen and the H-terminated surface. On platinum, however, we find that surface saturation with NH groups is necessary for ammonia production to occur. Regardless of the metal surface, the reaction is limited by the mass transport of atomic nitrogen, consistent with the weak dependence on catalyst material that we observe and has been reported by several other groups. This study represents a significant step toward achieving a mechanistic, microscopic-scale understanding of catalytic processes activated in low-temperature plasma environments.

We present the first application of field programmable gate arrays (FPGAs) as new, customizable hardware architectures for carrying out fast and energy-efficient quantum dynamics simulations of large chemical/material systems. Instead of tailoring the software to fixed hardware, which is the typical case for writing quantum chemistry code for central processing units (CPUs) and graphics processing units (GPUs), FPGAs allow us to directly customize the underlying hardware (even at the level of specific electrical signals in the circuit) to give a truly optimized computational performance for quantum dynamics calculations. By offloading the most intensive and repetitive calculations onto an FPGA, we show that the computational performance of our real-time electron dynamics calculations can even exceed that of optimized commercial mathematical libraries running on high-performance GPUs. In addition to this impressive computational speedup, we show that FPGAs are immensely energy-efficient and consume 4 times less energy than modern GPU or CPU architectures. These energy savings are a practical and important metric for supercomputing centers (many of which exceed over $1 million in power costs alone), as exascale computing capabilities become more widespread and commonplace. Taken together, the implementation techniques and performance metrics of our study demonstrate that FPGAs could play a promising role in upcoming quantum chemistry and materials science applications, particularly for the acceleration and energy-efficient execution of quantum dynamics calculations.

Per- and polyfluoroalkyl substances (PFASs) are synthetic chemicals that are harmful to both the environment and human health. Using self-interaction-corrected Born–Oppenheimer molecular dynamics simulations, we provide the first real-time assessment of PFAS degradation in the presence of excess electrons. In particular, we show that the initial phase of the degradation involves the transformation of an alkane-type C–C bond into an alkene-type C[double bond, length as m-dash]C bond in the PFAS molecule, which is initiated by the trans elimination of fluorine atoms bonded to these adjacent carbon atoms.

Enzymatic activity is crucial for various technological applications, yet the complex structures and limited stability of enzymes often hinder their use. Hence, de novo design of robust biocatalysts that are much simpler than their natural counterparts and possess enhanced catalytic activity has long been a goal in biotechnology. Here, we present evidence for the ability of a single amino acid to self-assemble into a potent and stable catalytic structural entity. Spontaneously, phenylalanine (F) molecules coordinate with zinc ions to form a robust, layered, supramolecular amyloid-like ordered architecture (F–Zn(II)) and exhibit remarkable carbonic anhydrase-like catalytic activity. Notably, amongst the reported artificial biomolecular hydrolases, F–Zn(II) displays the lowest molecular mass and highest catalytic efficiency, in addition to reusability, thermal stability, substrate specificity, stereoselectivity and rapid catalytic CO2 hydration ability. Thus, this report provides a rational path towards future de novo design of minimalistic biocatalysts for biotechnological and industrial applications.

Ab initio molecular dynamics (AIMD) is an indispensable tool for understanding the mechanistic details of external-energy-mediated chemical reactions. In this work, we show that the predicted thermodynamic and catalytic properties of certain reactions using AIMD simulations critically depend on the quality of the employed basis set. To this end, we have examined the reactants and products of the water–gas shift reaction (viz., CO, CO2, H2, and H2O) and studied their interaction with the ZnO(101̅0) surface using density functional theory and Born Oppenheimer molecular dynamics (BOMD) simulations. By merely increasing the quality of the basis, from double zeta (commonly used in most calculations of these systems) to triple zeta, we surprisingly find that the reaction outcome of a water (H2O) molecule colliding with a ZnO surface precovered with carbon monoxide (CO) gives qualitatively different results. These surprising results are shown to be robust with similar trends that are also obtained with other software packages. Furthermore, we show that the calculated adsorption energies can vary by as much as 380 meV (which is an order of magnitude larger than room temperature) by simply changing the basis set. Using electron density difference maps, we present mechanistic insight into the origin of these changes. Finally, we propose a simple diagnostic test that uses a single-point binding energy calculation to estimate the impact of basis-set quality, which can be used before carrying out a computationally expensive BOMD simulation.

We present the first application of machine learning on per- and polyfluoroalkyl substances (PFAS) for predicting and rationalizing carbon–fluorine (C–F) bond dissociation energies to aid in their efficient treatment and removal. Using a variety of machine learning algorithms (including Random Forest, Least Absolute Shrinkage and Selection Operator Regression, and Feed-forward Neural Networks), we were able to obtain extremely accurate predictions for C–F bond dissociation energies (with deviations less than 0.70 kcal/mol) that are within chemical accuracy of the PFAS reference data. In addition, we show that our machine learning approach is extremely efficient, requiring less than 10 min to train the data and less than a second to predict the C–F bond dissociation energy of a new compound. Most importantly, our approach only needs knowledge of the simple chemical connectivity in a PFAS structure to yield reliable results—without recourse to a computationally expensive quantum mechanical calculation or a three-dimensional structure. Finally, we present an unsupervised machine learning algorithm that can automatically classify and rationalize chemical trends in PFAS structures that would otherwise have been difficult to humanly visualize or process manually. Collectively, these studies (1) comprise the first application of machine learning techniques for PFAS structures to predict/rationalize C–F bond dissociation energies and (2) show immense promise for assisting experimentalists in the targeted defluorination of specific bonds in PFAS structures (or other unknown environmental contaminants) of increasing complexity.

Titanium nitride (TiN) offers advantages compared to standardly used plasmonic materials such as gold and silver in terms of thermal stability, cost, and sustainability. While gold and silver nanostructures have played an important role in the rapidly growing field of plasmonic catalysis, the potential of TiN in this application is still underexplored. Here we provide evidence of plasmon-driven chemical activity in TiN by using the photoreduction of platinum ions under visible–near-infrared (vis–NIR) illumination as probe reaction. An aqueous solution of TiN, methanol, and chloroplatinic acid (H2PtCl6) was exposed to vis–NIR radiation (600–900 nm). Scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) show nanostructures composed of ∼2 nm metallic platinum clusters decorating ∼10 nm TiN nanoparticles, confirming the plasmon-driven reduction of the Pt4+ ions to their metallic state. At the same time, the evolution of CO2 resulting from the photooxidation of methanol is monitored via gas chromatography. The molar Pt deposition-to-CO2 evolution ratio is in good agreement with the theoretical expectation based on the redox reaction charge balance. We have found that both Pt deposition and CO2 evolution are self-limiting. We attribute this to the increasing plasmon dephasing rate during the photoreduction process, likely due to the high optical losses of Pt in the vis–NIR region. In addition, density functional theory (DFT) simulations of a Pt(111)–TiN(111) junction suggest the existence of an energy barrier limiting electron transfer. This work confirms that plasmonic TiN nanoparticles can use visible light to drive photochemical reactions and highlights the potential of TiN as a cost-effective alternative to gold and silver.

Borophene, an elemental metallic Dirac material is predicted to have unprecedented mechanical and electronic character. Need of substrate and ultrahigh vacuum conditions for deposition of borophene restricts its large-scale applications and significantly hampers the advancement of research on borophene. Herein, a facile and large-scale synthesis of freestanding atomic sheets of borophene through a novel liquid-phase exfoliation and the reduction of borophene oxide is demonstrated. Electron microscopy confirms the presence of β12, X3, and their intermediate phases of borophene; X-ray photoelectron spectroscopy, and scanning tunneling microscopy, corroborated with density functional theory band structure calculations, validate the phase purity and the metallic nature. Borophene with excellent anchoring capabilities is used for sensing of light, gas, molecules, and strain. Hybrids of borophene as well as that of reduced borophene oxide with other 2D materials are synthesized, and the predicted superior performance in energy storage is explored. The specific capacity of borophene oxide is observed to be ≈4941 mAh g−1, which significantly exceeds that of existing 2D materials and their hybrids. These freestanding borophene materials and their hybrids will create a huge breakthrough in the field of 2D materials and could help to develop future generations of devices and emerging applications.

We develop a nonadiabatic dynamics propagation scheme that allows interfacing diabatic quantum dynamics methods with commonly used adiabatic electronic structure calculations. This scheme uses adiabatic states as the quasi-diabatic (QD) states during a short-time quantum dynamics propagation. At every dynamical propagation step, these QD states are updated based on a new set of adiabatic basis. Using the partial linearized density matrix (PLDM) path-integral method as one specific example for diabatic dynamics approaches, we demonstrate the accuracy of the QD scheme with a wide range of model nonadiabatic systems as well as the on-the-fly propagations with density functional tight-binding (DFTB) calculations. This study opens the possibility to combine accurate diabatic quantum dynamics methods with adiabatic electronic structure calculations for nonadiabatic dynamics propagations.

Even though transition metal dichalcogenides (TMDCs) are deemed to be novel photonic and optoelectronic 2D materials, the visible band gap being often limited to monolayer, hampers their potential in niche applications due to fabrication challenges. Uncontrollable defects and degraded functionalities at elevated temperature and under extreme environments further restrict their prospects. To address such limitations, the discovery of a new 2D material, α-PbO is reported. Micromechanical as well as sonochemical exfoliation of 2D atomic sheets of α-PbO are demonstrated and its optical behavior is investigated. Spectroscopic investigations indicate layer dependent band gaps. In particular, even multilayered PbO sheets exhibit visible band gap > 2 eV (direct) which is rare among semiconducting 2D materials. The emission lifetime of multilayer PbO atomic sheets is 7 ns (dim light) as compared to the monolayer which gives 2.5 ns lifetime and an intense light. Density functional theory calculations of layer dependent band structure of α-PbO matches well with experimental results. Experimental findings suggest that PbO atomic sheets exhibit hydrophobic nature, thermal robustness, microwave stability, anti-corrosive behaviour and acid resistance. This new low-cost, abundant and robust 2D material is expected to find many applications in the fields of electronics, optoelectronics, sensors, photocatalysis and energy storage.

We report the effect of strong spin orbit coupling inducing electronic topological and semiconductor to metal transitions on the thermoelectric material AgBiSe2 at high pressures. The synchrotron X-ray diffraction and the Raman scattering measurement provide evidence for a pressure induced structural transition from hexagonal (α-AgBiSe2) to rhombohedral (β-AgBiSe2) at a relatively very low pressure of around 0.7 GPa. The sudden drop in the electrical resistivity and clear anomalous changes in the Raman line width of the A1g and Eg(1) modes around 2.8 GPa was observed suggesting a pressure induced electronic topological transition. On further increasing the pressure, anomalous pressure dependence of phonon (A1g and Eg(1)) frequencies and line widths along with the observed temperature dependent electrical resistivity show a pressure induced semiconductor to metal transition above 7.0 GPa in β-AgBiSe2. First principles theoretical calculations reveal that the metallic character of β-AgBiSe2 is induced mainly due to redistributions of the density of states (p orbitals of Bi and Se) near to the Fermi level. Based on its pressure induced multiple electronic transitions, we propose that AgBiSe2 is a potential candidate for the good thermoelectric performance and pressure switches at high pressure.

A first-principles investigation of cubic BaRuO3, by combining density functional theory with dynamical mean-field theory and a hybridization expansion continuous time quantum Monte Carlo solver, has been carried out. Nonmagnetic calculations with appropriately chosen on-site Coulomb repulsion U and Hund's exchange J for single-particle dynamics and static susceptibility show that cubic BaRuO3 is in a spin-frozen state at temperatures above the ferromagnetic transition point. A strong redshift with increasing J of the peak in the real frequency dynamical susceptibility indicates a dramatic suppression of the Fermi liquid coherence scale as compared to the bare parameters in cubic BaRuO3. The self-energy also shows clear deviation from Fermi liquid behavior that manifests in the single-particle spectrum. Such a clean separation of energy scales in this system provides scope for an incoherent spin-frozen (SF) phase that extends over a wide temperature range, to manifest in non-Fermi liquid behavior and to be the precursor for the magnetically ordered ground state.

Optical unzipping of carbon nanotubes (CNTs) in liquid media is one of the most awaited technologies as it promises instant material transformation from CNTs to graphene nanoribbons (GNRs) and also an easy transfer of GNRs to arbitrary substrates. In the present article, we report the laser-induced optical unzipping of CNTs, dispersed in dimethylformamide (DMF) solvent. In a nutshell, laser unzipping of CNTs dispersed in liquid solvent is a photophysicochemical process where molecular interactions between CNTs and solvent are tuned by the laser irradiation and results in the formation of GNRs in a scalable manner. The proposed mechanism includes the creation of defects together with vacancies upon laser irradiation, followed by their migration toward the energetically favorable axis of the CNT—the longitudinal direction—finally leading to the unzipping/fragmentation of the nanotube. Distinct laser thresholds have been observed for each of the three events, namely, (a) the formation of the first defect, (b) vacancy migration along the longitudinal direction, and (c) fragmentation of CNTs into graphene nanosheets. Our experimental findings of the unzipping process have further been supported by the density functional theory (DFT) and density functional tight binding (DFTB) calculations performed on both single-walled and multiwalled CNTs.

The preparation of 1D WS2 and MoS2 flexible nanoribbons by laser-induced unzipping of the nanotubes is reported. The nanoribbons are of high quality, uniform width, and devoid of surface contamination. The zig-zag edges in WS2 nanoribbons give rise to ferromagnetism at room temperature.

Because of the advantages of tunability via size, shape, doping, and relatively low level of loss and high extent of spatial confinement, graphene quantum dots (GQDs) are emerging as an effective way to control light by molecular engineering. The collective excitation in GQDs shows high energy plasmon frequency along with frequencies in the terahertz (THz) region, making these systems powerful materials for photonic technologies. Here, we report a systematic study of the linear and nonlinear optical properties of large varieties of GQDs (∼400 systems) in size and topology utilizing the strengths of both semiempirical and first-principles methods. Our detailed study shows how the spectral shift and trends in the optical nonlinearity of GQDs depend on their structure, size, and shape. Among the circular, triangular, stripe, and random shaped GQDs, we find that GQDs with inequivalent sublattice atoms always possess lower HOMO–LUMO gap, broadband absorption, and high nonlinear optical coefficients. Also, we find that a majority of the GQDs with interesting linear and nonlinear optical properties have zigzag edges, although the reverse is not always true. We strongly believe that our findings can act as guidelines to design GQDs in optical parametric oscillators, higher harmonic generators, and optical modulators.

A hexanuclear Cu(I) cluster {Cu3(L)2}2 (1) based on a novel tripodal linker (L) has been synthesized. 1 shows intense emission (λmax = 560 nm) with lifetime 〈τ〉 = 224 μs and quantum yield = 27.6%. The emission is highly sensitive towards different electron rich and electron deficient aromatics. DFT calculations were performed to understand the origin of emission and sensing properties.

Utilizing the strengths of nitrogen-doped graphene quantum dot (N-GQD) as a substrate, herein, we have shown that one can stabilize the catalytically more active planar Au20 (P-Au20) compared with the thermodynamically more stable tetrahedral structure (T-Au20) on an N-GQD. Clearly, this simple route avoids the usage of traditional transition-metal oxide substrates, which have been suggested and used for stabilizing the planar structure for a long time. Considering the experimental success in the synthesis of N-GQDs and in the stabilization of Au nanoparticles on N-doped graphene, we expect our proposed method to stabilize planar structure will be realized experimentally and will be useful for industrial level applications.

First-principles spin-polarized calculations have been performed on passivated boron-nitride nanoribbons (BNNRs) with pentagon–heptagon line-defects (PHLDs), also called as Stone–Wales line-defects. Two kinds of PHLDs, namely, even-line and odd-line PHLDs, have been added either at one edge or at both edges of BNNRs. Single-edge (with all its different possibilities, for example, for a BNNR with 2-line PHLD at single-edge there are eight possibilities) as well as both-edge passivations have been considered for all the ribbons in this study by passivating each edge atom with hydrogen atom. Density of states (DOS) and projected-DOS analysis have been accomplished to understand the underlying reason for various properties. We find that passivation lead to different effects on the electronic and magnetic properties of a system, and the effects are mainly based on the line-defect introduced and/or on the atoms which are present at the passivated edge. In general, we find that, passivation can play a key role in tuning the properties of a system only when it has a zigzag edge.

Spin-polarized density functional theory calculations have been performed on armchair graphene quantum dots and boron-nitride quantum dots (AG/BNQDs) and the effect of carbon/boron-nitride substitution on the electronic properties of these AG/BNQDs has been investigated. As a first step to consider more realistic quantum dots, quantum dots which are a combination of zigzag QDs and armchair QDs have been considered. Effect of substitution on these hybrid quantum dots has been explored for both GQDs and BNQDs and such results have been compared and contrasted with the results of substituted AG/BNQDs and their zigzag analogs. Our work suggests that the edge substitution can play an important tool while tuning the electronic properties of quantum dots.

Using density functional theory calculations, we have examined the structural stability, electronic, magnetic, and optical properties of rectangular shaped quantum dots (QDs) of graphene (G), boron nitride (BN), and their hybrids. Different hybrid QDs have been considered by substituting a GQD (BNQD) with BN-pairs (carbon atoms) at different positions. Several parameters, like size, amount of substitution, and so forth, have been varied for all these QDs (GQDs, BNQDs, hybrid-QDs) to monitor the corresponding changes in their properties. Among the considered parameters, we find that substitution can act as a powerful tool to attain interesting properties with these QDs, for example, a broad range of absorption (∼2000 nm) in the near-infrared (NIR) region, spin-polarized HOMO–LUMO gaps without the application of any external-bias, and so forth, which are highly required in the preparation of opto-electronic and electronic/spintronic devices, among others. Explanations have been given in detail by varying different factors, like changing the position and amount of substitution, application of external electric field, and so forth, to ensure the reliability of our results.

Spin-polarized first-principles calculations have been performed to tune the electronic and optical properties of graphene (G) and boron-nitride (BN) quantum dots (QDs) through molecular charge-transfer using tetracyanoquinodimethane (TCNQ) and tetrathiafulvalene (TTF) as dopants. From our results, based on the formation energy and the distance between QDs and dopants, we infer that both the dopants are physisorbed on the QDs. Also, we find that GQDs interact strongly with the dopants compared to the BNQDs. Interestingly, although the dopants are physisorbed on QDs, their interactions lead to a decrement in the HOMO–LUMO gap of QDs by more than half of their original value. We have found a spin-polarized HOMO–LUMO gap in certain QD–dopant complexes. Mülliken population analysis, generation of density of states (DOS) and projected DOS (pDOS) plots, and optical conductivity calculations have been performed to support and understand the reasons behind our findings.

Spin-polarized first-principles calculations have been performed on zigzag boron–nitride nanoribbons (z-BNNRs) with lines of alternating fused pentagon (P) and heptagon (H) rings (pentagon–heptagon line defect) at a single edge as well as at both edges. The number of lines (n) of the pentagon–heptagon defect has been varied from 1 to 8 for 10-zBNNRs. Among the different spin-configurations that we have studied, we find that the spin-configuration with ferromagnetic ordering at each edge and antiferromagnetic ordering across the edges is quite interesting. For this spin-configuration, we find that, if the introduced PH line defect is odd-numbered, the systems behave as spin-polarized semiconductors, but, for even-numbered, all the systems show interesting antiferromagnetic half-metallic behavior. Robustness of these results has been cross checked by the variation of the line-defect position and also by the variation of the width [from ∼1.1 nm (6-zBNNR) to ∼3.3 nm (16-zBNNR)] of the ribbon. Density of states (DOS), projected DOS, and band-structure analysis have been accomplished to understand the reasons for these differences between even and odd line defects. The main reason for many of the observed changes was traced back to the change in edge nature of the BNNR, which indeed dictates the properties of the systems.

The interaction of halogen molecules of varying electron affinity, such as iodine monochloride (ICl), bromine (Br₂), iodine monobromide (IBr) and iodine (I₂) with single-walled carbon nanotubes (SWNTs) and graphene has been investigated in detail. Halogen doping of the two nanocarbons has been examined using Raman spectroscopy in conjunction with electronic absorption spectroscopy and extensive theoretical calculations. The halogen molecules, being electron withdrawing in nature, induce distinct changes in the electronic states of both the SWNTs and graphene, which manifests with a change in the spectroscopic signatures. Stiffening of the Raman G-bands of the nanocarbons upon treatment with the different halogen molecules and the emergence of new bands in the electronic absorption spectra, both point to the fact that the halogen molecules are involved in molecular charge-transfer with the nanocarbons. The experimental findings have been explained through density functional theory (DFT) calculations, which suggest that the extent of charge-transfer depends on the electron affinities of the different halogens, which determines the overall spectroscopic properties. The magnitude of the molecular charge-transfer between the halogens and the nanocarbons generally varies in the order ICl > Br₂ > IBr > I_2, which is consistent with the expected order of electron affinities.

Time-dependent density functional theory (TDDFT) calculations have been used to understand the excited-state properties of modified chlorophyll f (Chlide f), Chlide a, Chlide b, and axial ligated (with imidazole, H₂O, CH₃OH, CH₃COOH, C₆H₅OH) Chlide f molecules. The computed differences among the Q_x, Q_y, B_x, and B_y band absorbance wavelengths of Chlide a, b, and f molecules are found to be comparable with the experimentally observed shifts for these bands in chlorophyll a (chl a), chl b, and chl f molecules. Our computations provide evidence that the red shift in the Q_y band of chl f is due to the extended delocalization of macrocycle chlorin ring because of the presence of the −CHO group. The local contribution from the −CHO substituent to the macrocycle chlorin ring stabilizes the corresponding molecular orbitals (lowest unoccupied molecular orbital (LUMO) of the Chlide f and LUMO–1 of the Chlide b). All the absorption bands of Chlide f shift to higher wavelengths on the addition of axial ligands. Computed redox potentials show that, among the axial ligated Chlide f molecules, Chlide f–imidazole acts as a good electron donor and Chlide f–CH₃COOH acts as a good electron acceptor.