Role of anchoring groups on the light harvesting and optoelectronic properties of triphenylamine derivatives: insights from theory.

BACKGROUND: In the present work, DFT and time-dependent DFT calculations were performed to investigate the role of anchoring groups on the photophysical properties and reveal structure-property correlations of triphenylamine (TPA) derivatives. The selected anchoring groups are tetrazole, acrylamide, hydantoin, and rhodanine. RESULTS: Our results show that the different anchoring groups employed alter the planarity, intramolecular charge transfer properties, and HOMO-LUMO gap and hence influence the optoelectronic properties of the dyes. Although all molecules fulfill the basic requirements with suitable energy levels, band gap, absorption, and charge transfer properties, the dye with rhodanine acceptor (TPA4) was the most promising candidate due to its lowest HOMO-LUMO gap, red-shifted highest λmax absorption value, better ICT pattern, low total reorganization energy, and good electron injection properties. Overall, it is anticipated that the results of this investigation will point to new avenues for the experimental fabrication of remarkably effective metal-free organic dyes for solar cell applications.

DFT insights into the mechanism of O2 activation catalyzed by a structural and functional model of cysteine dioxygenase with tris(2-pyridyl)methane-based ligand architecture.

Cysteine dioxygenation is an important step in the metabolism of toxic L-cysteine (Cys) in the human body, carried out by cysteine dioxygenase enzyme (CDO). The disruption of this process is found to elicit neurological health issues. This work reports a computational investigation of mechanistic aspects of this reaction, using a recently reported tris(2-pyridyl)methane-based biomimetic model complex of CDO. The computed results indicate that, the initial SO2 bond formation process is the slowest step in the S-dioxygenation process, possessing an activation barrier of 12.7 kcal/mol. The remaining steps were found to be downhill requiring very small activation energies. The transition states were found to undergo spin crossover between triplet and quintet states, while the singlet surface remained unstable throughout the entire reaction. In essence, the mechanistic scheme and multistate reactivity pattern together with the relatively small computed rate-limiting activation barrier as well as the exothermic formation energy demonstrate that the model complex is an efficient biomimetic CDO model. In addition, the study also substantiates the involvement of Fe(IV)oxido intermediates in the mechanism of S-dioxygenation by the chosen model complex. The insights derived from the O2 activation process might pave way for development of more accurate CDO model catalysts that might be capable of even more efficiently mimicking the geometric, spectroscopic and functional features of the CDO enzyme.

Halogen-Based 17ß-HSD1 Inhibitors: Insights from DFT, Docking, and Molecular Dynamics Simulation Studies.

The high expression of 17ß-hydroxysteroid dehydrogenase type 1 (17ß-HSD1) mRNA has been found in breast cancer tissues and endometriosis. The current research focuses on preparing a range of organic molecules as 17ß-HSD1 inhibitors. Among them, the derivatives of hydroxyphenyl naphthol steroidomimetics are reported as one of the potential groups of inhibitors for treating estrogen-dependent disorders. Looking at the recent trends in drug design, many halogen-based drugs have been approved by the FDA in the last few years. Here, we propose sixteen potential hydroxyphenyl naphthol steroidomimetics-based inhibitors through halogen substitution. Our Frontier Molecular Orbitals (FMO) analysis reveals that the halogen atom significantly lowers the Lowest Unoccupied Molecular Orbital (LUMO) level, and iodine shows an excellent capability to reduce the LUMO in particular. Tri-halogen substitution shows more chemical reactivity via a reduced HOMO-LUMO gap. Furthermore, the computed DFT descriptors highlight the structure-property relationship towards their binding ability to the 17ß-HSD1 protein. We analyze the nature of different noncovalent interactions between these molecules and the 17ß-HSD1 using molecular docking analysis. The halogen-derived molecules showed binding energy ranging from -10.26 to -11.94 kcal/mol. Furthermore, the molecular dynamics (MD) simulations show that the newly proposed compounds provide good stability with 17ß-HSD1. The information obtained from this investigation will advance our knowledge of the 17ß-HSD1 inhibitors and offer clues to developing new 17ß-HSD1 inhibitors for future applications.

DFT Probe into the Mechanism of Formic Acid Dehydrogenation Catalyzed by Cp*Co, Cp*Rh, and Cp*Ir Catalysts with 4,4'-Amino-/Alkylamino-Functionalized 2,2'-Bipyridine Ligands.

The mechanistic landscape of H2 generation from formic acid catalyzed by Cp*M(III) complexes (M = Co or Rh or Ir) with diamino-/dialkylamino-substituted 2,2'-bipyridine ligand architectures have been unveiled computationally. The calculations indicate that the ß-hydride elimination process is the rate-determining step for all the investigated catalysts. The dialkylamino moieties on the 2,2'-bipyridine ligand were found to reduce the activation free energy required for the rate-limiting ß-hydride elimination step and increase the hydridic nature of the Ir-hydride bond, which accounts for the experimentally observed enhanced catalytic activity. Furthermore, the protonation by H3O+ ion was found to be the kinetically most favorable route than the conventional protonation by formic acid. The origin for this preference lies in the increased electrophilicity of the proton from hydronium ion which facilitates easy protonation of the metal-hydride with low activation energy barrier. The Co and Rh analogues of the chosen iridium catalyst were computationally designed and were estimated to possess a rate-determining activation barrier of 16.9 and 14.5 kcal/mol, respectively. This illustrates that these catalysts are potential candidates for FAD. The insights derived in this work might serve as a vital knowledge that could be capitalized upon for designing cost-effective catalyst for FAD in future.

Deciphering the Mechanistic Details of Manganese-Catalyzed Formic Acid Dehydrogenation: Insights from DFT Calculations.

A comprehensive density functional theory investigation has been carried out to unravel the complete mechanistic landscape of aqueous-phase formic acid dehydrogenation (FAD) catalyzed by a pyridyl-imidazoline-based Mn(I) catalyst [Mn(PY-NHIM)(CO)3Br], which was recently reported by Beller and co-workers. The computed free energy profiles show that for the production of a Mn-formate intermediate [Mn(HCO2-)], a stepwise mechanism is both kinetically and thermodynamically favorable compared to the concerted mechanism. This stepwise mechanism involves the dissociation of a Br- ion from a Mn-bromide complex [Mn(Br)] to create a vacant site and coordination of water solvent to this vacant site, followed by the dissociative exchange of the aqua ligand with the formate ion to form Mn(HCO2-). Non-covalent interaction analysis revealed that the steric hindrance at the transition state is the cardinal reason for the preference to a stepwise mechanism. The ß-hydride elimination process was estimated to be the rate-determining step with a barrier of 19.0 kcal/mol. This confirms the experimental observation. The generation of a dihydrogen-bound complex was found to occur through the protonation of Mn-hydride by a hydronium ion instead of formic acid. The mechanistic details and insights presented in this work would promote future catalytic designing and exploration of earth-abundant Mn-based catalytic systems for potential applications toward FAD.

Pathways of the Extremely Reactive Iron(IV)-oxido complexes with Tetradentate Bispidine Ligands.

The nonheme iron(IV)-oxido complex trans-N3-[(L1 )FeIV =O(Cl)]+ , where L1 is a derivative of the tetradentate bispidine 2,4-di(pyridine-2-yl)-3,7-diazabicyclo[3.3.1]nonane-1-one, is known to have an S=1 electronic ground state and to be an extremely reactive oxidant for oxygen atom transfer (OAT) and hydrogen atom abstraction (HAA) processes. Here we show that, in spite of this ferryl oxidant having the "wrong" spin ground state, it is the most reactive nonheme iron model system known so far and of a similar order of reactivity as nonheme iron enzymes (C-H abstraction of cyclohexane, -90 °C (propionitrile), t1/2 =3.5 sec). Discussed are spectroscopic and kinetic data, supported by a DFT-based theoretical analysis, which indicate that substrate oxidation is significantly faster than self-decay processes due to an intramolecular demethylation pathway and formation of an oxido-bridged diiron(III) intermediate. It is also shown that the iron(III)-chlorido-hydroxido/cyclohexyl radical intermediate, resulting from C-H abstraction, selectively produces chlorocyclohexane in a rebound process. However, the life-time of the intermediate is so long that other reaction channels (known as cage escape) become important, and much of the C-H abstraction therefore is unproductive. In bulk reactions at ambient temperature and at longer time scales, there is formation of significant amounts of oxidation product - selectively of chlorocyclohexane - and it is shown that this originates from oxidation of the oxido-bridged diiron(III) resting state.

Substituent Effect on the Photophysics and ESIPT Mechanism of N,N'-Bis(salicylidene)-p-phenylenediamine: A DFT/TD-DFT Analysis.

Excited-state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT) processes are widely exploited in the designing of organic materials for multifarious applications. This work explores the aftereffects of combining both ESIPT and ICT events in a single molecule, namely, N,N'-bis(salicylidene)-p-phenylenediamine (BSP) exploiting DFT and TD-DFT formalisms. The PBE0 functional employed in the present study is found to yield results with better accuracy for excited-state calculations. The results reveal that introduction of electron donor (-NH2) and electron acceptor (-NO2) substituents on BSP produces a strikingly red-shifted emission with respect to the corresponding emission from the unsubstituted analogue in polar solvents. This red-shifted emission originated due to the coupled effect of ESIPT and planar-ICT (PICT) processes from the coplanar geometry adopted by the substituted molecule (s-BSP). Based on the computed potential energy curves, the ground-state intramolecular proton transfer (GSIPT) was found to take place more favorably in s-BSP than in BSP under all solvent conditions. In the case of ESIPT, the barrier and relative energies of the phototautomers of s-BSP were slightly higher than BSP, which shows that simultaneous substitution of -NH2 and -NO2 groups causes slight perturbation to the ESIPT process. Overall, the computed results show that simultaneous substitution of suitable electron donor and acceptor substituents provides profitable changes in the photophysical properties of ESIPT molecules like BSP. These molecular-level insights will pave way for designing better materials for diverse applications.

The keto-enol tautomerization of ethyl acetoacetate in choline ionic liquids: the role of cation and anion in switching the tautomeric equilibrium.

In this work, density functional theory (DFT) calculations were carried out to study the role of the explicit treatment of four different choline-based ionic liquids (CS, CP, NS, and NP) by utilizing two different cations and anions in the tautomeric equilibrium of ethyl acetoacetate (EAA). The involvement of the acidic N-H proton from the cationic part of NS and NP ionic liquid offers the possibility to have two more additional transition states for the tautomeric equilibrium of EAA. The computed results demonstrated that a high activation free energy barrier (ΔG = 49.4 kcal mol-1) is associated with the direct enol to keto (E → K) interconversion via a 4-membered ring transition state. Upon explicit involvement of the cationic part of ionic liquids in the tautomeric equilibrium via a 6-membered ring transition state (CAT), ΔG is substantially reduced to 21.88 kcal mol-1. Further, ΔG is drastically reduced to 10.57 kcal mol-1 upon the involvement of the anionic part of the ionic liquid explicitly via an 8-membered ring transition state (AAT). The W-shaped TS in the CAT pathway causes steric hindrance and increases the energy penalty, while the sickle-shaped TS in AAT facilitates easy proton transfer without the influence of the steric factor. In addition, the RDG scatter graphs predict large negative values of ρ*, which indicate that the hydrogen bonding network in AAT is stronger, enhancing the delocalization of the electron density. The QTAIM analysis substantiated the role of intermolecular hydrogen bonding interactions between the ionic liquid and EAA and within the anion-cation pair in stabilizing the keto group of EAA. Besides, the involvement of the acidic N-H proton in the transition state is the key factor in influencing the energetics of the keto-enol tautomerization reaction. The present study illustrates molecular-level insights into the role of individual ions of ionic liquids and also provides adequate ideas for designing novel ionic liquid-based catalysts for industrially relevant chemical reactions.

Internet of Things-Enabled Aggregation-Induced Emission Probe for Cu2+ Ions: Comprehensive Investigations and Three-Dimensional Printed Portable Device Design.

Herein, we have developed a novel aggregation-induced emission (AIE) probe and three-dimensional (3D) printed portable device for copper (Cu2+) sensing in an aqueous medium. A ubiquitous synthetic route has been employed to devise the anthracene-conjugated imidazo[1,5-a]pyridine (TL19) probe as a unique anchor for Cu2+ ions. The TL19 is meticulously characterized through pivotal spectroscopic techniques, and the satisfactory results were obtained. The solvatochromic analysis and density functional theory calculations cohesively reveal that the TL19 exhibits the intramolecular charge transfer transition upon photoexcitation. Intriguingly, the TL19 exhibits spherically shaped nanoaggregates and enhanced fluorescence in DMSO/water (10:90) mixtures. This fluorescent nanoaggregate instantaneously responded toward the detection of Cu2+ via a deaggregation mechanism. The detection limit is found to be 9 pM in an aqueous medium. Further, the detection of Cu2+ in the HeLa cells has also been achieved due to bright green fluorescence, photostability, and biocompatibility nature of TL19 aggregates. On the other hand, an internet of things (IoT)-embedded 3D printed portable device is constructed for the detection of Cu2+ ions in real water samples. The Cu2+ detection is achieved through an IoT device, and results were acknowledged through an android application in 3.32 s round-trip time. Thus, the IoT-enabled AIE probe could be a prospective device for Cu2+ detection in a constrained environment.

IoT-enabled dye-sensitized solar cells: an effective embedded tool for monitoring the outdoor device performance.

Herein, we have developed a tool for monitoring the outdoor performance of dye-sensitized solar cells. In this regard, a new dye consisting of an N-aryl-substituted imidazole with N-alkylated carbazole as the donor and cyanoacrylic acid as the acceptor has been designed. The overall power conversion efficiency of the designed dye reached ∼50%, with respect to that of the N719-based device (4%) under similar experimental conditions. Further, the device was interfaced with an IoT system, which measured the voltage and transmitted the device parameters to the user's mobile phone through a cloud channel. The developed IoT tool provides a resolution of 0.0315 mV and a round-trip delay time of <0.32 s for transmitting the information to the user's mobile phone.

Pyrene-Based Chemosensor for Picric Acid-Fundamentals to Smartphone Device Design.

Developing a fluorescent probe for the selective and sensitive detection of explosives is a topic of continuous research interest. Additionally, underlying the principles behind the detection mechanism is indeed providing substantial information about the design of an efficient fluorescence probe. In this context, a pyrene-tethered 1-(pyridin-2-yl)imidazo[1,5-a]pyridine-based fluorescent probe (TL18) was developed and employed as a fluorescent chemosensor for nitro explosives. The molecular structure of TL18 was well-characterized by NMR and EI-MS spectrometric techniques. UV-visible absorption, steady-state, and time-resolved fluorescence spectroscopic techniques have been employed to explicate the photophysical properties of TL18. The fluorescent nature of the TL18 probe was explored for detection of nitro explosives. Intriguingly, the TL18 probe was selectively responsive to picric acid over other explosives. The quantitative analysis of the fluorescence titration studies of TL18 with picric acid proved that the probe achieved a detection limit of 63 nM. Further, DFT and QTAIM studies were used to establish the nature of the sensing mechanism of TL18. The hydrogen-bonding interactions are the reason for the imperative sensing property of TL18 for picric acid. Thus, our experimental and theoretical studies provide an adequate and appropriate prerequisite for an efficient fluorescent probe. Furthermore, a smartphone-interfaced portable fluorimeter module is developed to facilitate sensitive and real-time sensing of picric acid. This portable module was capable of detecting picric acid down to 99 nM. Eventually, these studies will have a significant impact on development and application of a new class of chemosensors for detection of explosives.

A Structural and Functional Model for the Tris-Histidine Motif in Cysteine Dioxygenase.

The iron(II) complexes [Fe(L)(MeCN)3 ](SO3 CF3 )2 (L are two derivatives of tris(2-pyridyl)-based ligands) have been synthesized as models for cysteine dioxygenase (CDO). The molecular structure of one of the complexes exhibits octahedral coordination geometry and the Fe-Npy bond lengths [1.953(4)-1.972(4) Å] are similar to those in the Cys-bound FeII -CDO; Fe-NHis : 1.893-2.199 Å. The iron(II) centers of the model complexes exhibit relatively high FeIII/II redox potentials (E1/2 =0.988-1.380 V vs. ferrocene/ferrocenium electrode, Fc/Fc+ ), within the range for O2 activation and typical for the corresponding nonheme iron enzymes. The reaction of in situ generated [Fe(L)(MeCN)(SPh)]+ with excess O2 in acetonitrile (MeCN) yields selectively the doubly oxygenated phenylsulfinic acid product. Isotopic labeling studies using 18 O2 confirm the incorporation of both oxygen atoms of O2 into the product. Kinetic and preliminary DFT studies reveal the involvement of an FeIII peroxido intermediate with a rhombic S= 1 / 2 FeIII center (687-696 nm; g≈2.46-2.48, 2.13-2.15, 1.92-1.94), similar to the spectroscopic signature of the low-spin Cys-bound FeIII CDO (650 nm, g≈2.47, 2.29, 1.90). The proposed FeIII peroxido intermediates have been trapped, and the O-O stretching frequencies are in the expected range (approximately 920 and 820 cm-1 for the alkyl- and hydroperoxido species, respectively). The model complexes have a structure similar to that of the enzyme and structural aspects as well as the reactivity are discussed.

Theoretical Investigation of Steric Effect Influence on Reactivity of Substituted Butadienes with Bromocyclobutenone.

The Diels-Alder reaction (DA) between various mono- and disubstituted 1,3-butadiene (Dn-1 to Dn-10) and 2-bromocyclobutenone (DPh) was carried out in gas phase using density functional theory (DFT) at the M06-2X/6-31+g** level. The reaction was found to proceed through a concerted asynchronous transition state. Further, the asynchronous and early nature of the transition state was clearly pinpointed with the frontier molecular orbital (FMO) and bond order index (BOI) analyses. The intermolecular hydrogen bonding interaction along with steric encumbrance in the transition state were found to be the predominant factors in controlling the reactivity of the dienes. Among the investigated dienes, Dn-6 was found to be the most reactive diene which is attributed to its low activation barrier due to the presence of strong intermolecular H-bonding interactions. These factors were further supported by quantum mechanical calculations using global descriptor indexes, natural bond orbital analysis, and quantum theory of atoms in molecules analysis. These theoretical results were found to be in good agreement with the previous experimental findings.

Role of Anation on the Mechanism of Proton Reduction Involving a Pentapyridine Cobalt Complex: A Theoretical Study.

Kinetic and thermodynamic aspects of proton reduction involving pentapyridine cobalt(II) complex were investigated with the help of quantum chemical calculations. Free energy profile of all possible mechanistic routes for proton reduction was constructed with the consideration of both anation and solvent bound pathways. The computed free energy profile shows that acetate ion plays a significant role in modulating the kinetic aspects of Co(III)-hydride formation which is found to be the key intermediate for proton reduction. Upon replacing solvent by acetate ion, one electron reduction and protonation of CoI species become more rapid along with slow displacement reaction. Most favorable pathways for hydrogen evolution from Co(III)-hydride species is also investigated. Among the four possible pathways, reduction followed by protonation of Co(III)-hydride (RPP) is found to be the most feasible pathway. On the basis of QTAIM and NBO analyses, the electronic origin of most favorable pathway is explained. The basicity of cobalt center along with thermodynamic stability of putative CoIII/II-H species is essentially a prime factor in deciding the most favorable pathway for hydrogen evolution. Our computed results are in good agreement with experimental observations and also provided adequate information to design cobalt-based molecular electrocatalysts for proton reduction in future.

A combined experimental and computational investigation on pyrene based D-π-A dyes.

The geometry (twist vs. planar) of a dye is one of the most pivotal factors for determining intramolecular charge transfer (ICT), light harvesting and photovoltaic properties of dye-sensitized solar cells. In order to comprehend the role of dye geometry on the above properties, we have devised the pyrene based D-π-A dyes namely 2-cyano-3-(5-pyren-1-yl-furan-2-yl)-acrylic acid (PFCC) and 2-cyano-3-(5-pyren-1-ylethynyl-furan-2-yl)-acrylic acid (PEFCC). The synthesized pyrene dyes were well characterized by NMR and EI-MS spectrometry. In both the dyes, the donor (pyrene) and acceptor (cyanoacrylic acid) segments remained the same. The varied π-spacers were furan and ethynyl furan. The influences of the ethynyl spacer on the energy levels, light absorption, dynamics of excited states and photovoltaic properties of the DSCs were systematically investigated via theoretical calculations and spectroscopic measurements. UV-visible absorption spectral measurements indicated that the introduction of the ethynyl spacer enhances the molar absorptivity of a dye (PEFCC) in the order of 2, but does not shift the absorption range, which is consistent with the results obtained from density functional theory (DFT) calculations. The theoretical analysis indicated that the charge transfer transition is mainly constituted of the HOMO to the LUMO that were found to be located on donor and acceptor segments, respectively, which is supportive for efficient charge separation and electron injection processes. TDDFT calculations highlighted that the LUMO of the PEFCC dye is more stabilized by the incorporation of the ethynyl group between the pyrene and furan moieties that aid to inject electrons efficiently into TiO2 thereby resulting in an enhanced power conversion efficiency of 2.47% when compared to the PFCC dye. Notably, the overall conversion efficiency of the PEFCC dye reached 60% with respect to that of an N719-based device (4.12%) fabricated under similar conditions. Transient absorption kinetic studies demonstrated that a slower charge recombination rate is an essential factor behind enhanced efficiencies in PEFCC based cells.

Unusual intramolecular CHO hydrogen bonding interaction between a sterically bulky amide and uranyl oxygen.

The selective separation of toxic heavy metals such as uranyl can be accomplished using ligands with stereognostic hydrogen bonding interactions to the uranyl oxo group, as proposed by Raymond and co-workers (T. S. Franczyk, K. R. Czerwinski and K. N. Raymond, J. Am. Chem. Soc., 1992, 114, 8138-8146). Recently, several ligands possessing this weak interaction have been proposed involving the hydrogen bonding of NH and OH based moieties with uranyl oxygen. We herein report the structurally and spectroscopically characterized CHO hydrogen bonding using a sterically bulky amide based ligand. In conjunction with experiments, electronic structure calculations are carried out to understand the structure, binding and the strength of the CHO hydrogen bonding interactions. This weak interaction is mainly due to the steric effect caused by a bulky substituent around the donor group which has direct relevance in designing novel ligands in nuclear waste management processes. Although the kinetics are very slow, the ligand is also highly selective to uranyl in the presence of other interfering ions such as lanthanides.

Mechanistic insights into intramolecular ortho-amination/hydroxylation by nonheme FeIV[double bond, length as m-dash]NTs/FeIV[double bond, length as m-dash]O species: the σ vs. the π channels.

Comparative oxidative abilities of nonheme FeIV[double bond, length as m-dash]NTs and FeIV[double bond, length as m-dash]O species using DFT has been explored. Our calculations reveal that the FeIV[double bond, length as m-dash]NTs is found to be a stronger oxidant in two electron transfer reactions and react exclusively via π channels while the FeIV[double bond, length as m-dash]O species is found to be a stronger oxidant when the σ-pathway is activated such as in HAT reactions.

The role of π-linkers in tuning the optoelectronic properties of triphenylamine derivatives for solar cell applications - A DFT/TDDFT study.

A recently reported triphenylamine (TPA) group in conjugation with a benzothiadiazole (BTD) moiety opens up the possibility for designing new organic sensitizers for solar cell applications that are amenable for structural tuning. Hence, seven new TPA molecules were designed from two experimentally reported molecules. The optoelectronic properties, including the absorption and emission spectra of the TPA derivatives, were studied via density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. Different π-linkers were screened to understand the role of π-linkers in altering the optoelectronic properties of these molecules. Our results show that furan moieties bring planarity to the molecule and show reduced HOMO-LUMO gaps. All these molecules show excellent delocalization of π-electrons. TDDFT calculations show that furan-substituted TPA (TPA9) has the highest absorption maxima. Interestingly, the thiophene-substituted TPA (TPA7) was found to have a high emission maxima as it achieved planarity in the excited state. There is an excellent correlation observed between the computed optoelectronic properties and calculated HOMO-LUMO gaps. Overall, this study throws light on the role of π-linkers in the photophysical properties of TPA derivatives and provides useful clues in designing new molecules for optoelectronic applications.

Pyrene based D-π-A architectures: synthesis, density functional theory, photophysics and electron transfer dynamics.

Pyrene derivatives show immense potential as sensitizers for dye-sensitized solar cells (DSCs). Therefore, this work focuses on the impact of π-spacers on the photophysical, electrochemical and photovoltaic properties of pyrene based D-π-A dyes, since the insertion of π-spacers is one of the doable strategies to improve the light harvesting properties of the dye. In this respect, three new pyrene based D-π-A dyes have been synthesized and characterized by 1H, 13C NMR, and elemental analyses and EI-MS spectrometry. The selected π-spacers are benzene, thiophene and furan. Compared with a benzene spacer, the introduction of a heterocyclic ring spacer reduces the band gap of the dye and brings about the broadening of the absorption spectra to the longer wavelength region through intramolecular charge-transfer (ICT). Combined experimental and theoretical studies were performed to investigate the ICT process involved in the pyrene derivatives. The profound solvatochromism with increased nonradiative rate constants (knr) has been construed in terms of ICT from the pyrene core to rhodanine-3-acetic acid via conjugated π-spacers. Electrochemical data also reveal that the HOMO and LUMO energy levels are fine-tuned by incorporating different π-spacers between pyrene and rhodanine-3-acetic acid. On the basis of the optimized DSC test conditions, the best performance was found for PBRA, in which a benzene group is the conjugated π-spacer. The divergence in the photovoltaic behaviors of these dyes was further explicated by femtosecond fluorescence and electrochemical impedance spectroscopy.

Unravelling the effect of anchoring groups on the ground and excited state properties of pyrene using computational and spectroscopic methods.

Anchoring groups play an important role in dye sensitized solar cells (DSCs). In order to acquire a suitable anchoring group for DSCs, a deeper understanding of the effect of anchoring groups on the ground and excited state properties of the dye is significant. In this context, various anchoring group connected pyrene derivatives are successfully synthesized and well characterized by using (1)H, (13)C-NMR, FT-IR and EI-MS spectrometry. The anchoring groups employed are carboxylic acid, malonic acid, acrylic acid, malononitrile, cyanoacrylic acid, rhodanine and rhodanine-3-acetic acid. The optimized geometries, HOMO-LUMO energy gap, light harvesting efficiency (LHE) and electronic absorption spectra of these dyes are studied by using density functional theory (DFT) calculations. The results show that pyrene connected with anchoring groups with weak electron pulling strength (PC, PAC and PMC) has a larger HOMO-LUMO energy gap, whereas that connected with anchoring groups with strong electron pulling strength (PCC, PMN, PR and PRA) has a reduced HOMO-LUMO energy gap. These molecules with a reduced energy gap are primarily preferred for DSC applications. Moreover, P, PC, PAC and PMC molecules undergo π→π* transition, whereas PCC, PMN, PR and PRA molecules show significant charge transfer along with π→π* transition. UV-visible absorption spectral studies on these dyes reveal that connecting various anchoring groups with different electron pulling abilities enables the pyrene chromophore to absorb in the longer wavelength region. Notably, an efficient bathochromic shift is observed for PCC, PMN, PR and PRA molecules in both electronic absorption and fluorescence spectral measurements, which suggests that the excitation is delocalized throughout the entire π-system of the molecules. Both theoretical and spectral studies reveal that dyes with an ICT character (PCC, PMN, PR and PRA) are suitable for dye sensitized solar cell applications.