HOMO-LUMO Transition Research Articles

Synthesis of n-type [60]Fullerene Derivatives with Sterically Bulky tert-Butyl Groups for Vacuum Deposition Processes.

[60]Fullerene derivatives with high thermal stability can be used for vacuum deposition under heating to fabricate thin films for organic electronic devices. Here, we investigated the thermal stability of [60]fullerene derivatives with various bulky substituents for thermal evaporation under vacuum by means of thermogravimetric analysis under reduced and normal pressure. We found sterically bulky groups such as tert-butyl groups of [60]fullerene derivatives lowered the vacuum deposition temperature. Also, we performed isothermal thermogravimetric analysis to examine the long-term thermal stability of the designed compounds under heating conditions. Furthermore, we investigated the UV-Vis absorption patterns of the deposited films. Absorption in the blue wavelength range, which was attributed to intermolecular HOMO-LUMO transitions among the molecular orbitals of adjacent [60]fullerenes, was dramatically modified. These results were associated with the prevention of aggregation among neighboring [60]fullerene by the sterically bulky groups. This concept could contribute to expanding the use of evaporable [60]fullerene derivatives in organic thin-film electronics research fields.

Four-Coordinate Monoboron Complexes with 8-Hydroxyquinolin-5-Sulfonate: Synthesis, Crystal Structures, Theoretical Studies, and Luminescence Properties

8-Hydroxyquinolin-5-sulfonic acid (8HQSA) was combined with 3-pyridineboronic acid (3PBA) or 4-pyridineboronic acid (4PBA) to give two zwitterionic monoboron complexes in crystalline form. The compounds were characterized by elemental analysis, single-crystal X-ray diffraction studies, and IR, 1H NMR, UV-Visible, and luminescence spectroscopy. The analyses revealed compounds with boron atoms adopting tetrahedral geometry. In the solid state, the molecular components are linked by charge-assisted (B)(O−H⋯−O(S) and N+−H⋯O(S) hydrogen bonds aside from C−H⋯O contacts and π⋯π interactions, as shown by Hirshfeld surface analyses and 2D fingerprint plots. The luminescence properties were characterized in terms of the emission behavior in solution and the solid state, showing emission in the bluish-green region in solution and large positive solvatofluorochromism, caused by intramolecular charge transfer. According to TD-DFT calculations at the M06-2X/6-31G(d) level of theory simulating an ethanol solvent environment, the emission properties are originated from π-π * and n-π * HOMO-LUMO transitions.

Synthesis and characterisation of formohydrazide derivatives as potential antimicrobial agents: molecular docking and DFT studies

A novel series of formohydrazide derivatives (3a-3j) were synthesised and characterised by FT-IR, 1H and 13C NMR spectral techniques. The geometrical parameters of compound 3d were calculated by using the DFT method B3LYP/6-311++G(d,p) basis set. The title molecule's dipole moment, polarizability, and first-order hyperpolarizability were calculated and interpreted. The HOMO–LUMO transition occurs when a molecule undergoes intra-molecular charge transfer. The reactive sites of the molecule are studied using the Molecular Electrostatic Potential (MEP) surface. In addition, using the DFT/B3LYP/6-311++G(d,p) level of theory, the Mulliken atomic charges of carbon, nitrogen, oxygen, chlorine, and hydrogen atoms were determined. The compounds 3a-j were tested for their in vitro antibacterial activity against five bacterial strains viz., Gram-Positive bacteria species Enterococcus faecalis, Staphylococcus aurous and Gram-Negative bacteria species Escherichia coli, Klebsiella pneumonia and Pseudomonas aeruginosa. The tested antimicrobial activities of the compounds were compared with the standard drug of Ciprofloxacin for bacteria and Ketocanazone for fungal. The compounds 3c, 3d and 3e showed excellent antifungal activities than the standard fungal strains. Molecular docking analysis was used to investigate the interaction of the title compound with a target protein.

Intermolecular CH-π Electrons Interaction in Poly (9,9-dioctylfluorenyl-2,7-diyl) (PFO): An Experimental and Theoretical Study.

This study demonstrates the presence of CH-π interaction in poly [9,9-dioctylfluorenyl-2,7-diyl] (PFO-1) due to an aggregate formation of PFO-1 in the liquid state. The absorption spectra of PFO-1 in certain solvents at low concentrations showed a single band at 390 nm. However, when using high concentrations, a new band at 437 nm appeared. This band is due to the aggregate formation of PFO-1. The aggregate formation occurs as a result of the CH interaction of the n-alkyl side chains with π-electrons in the benzene ring. The optical characteristics of another conjugated polymer of poly [9,9-di-(2-ethylhexyl)-fluorenyl-2,7-diyl] (PFO-2) were investigated to confirm the CH-π interaction. The absorption showed only one wavelength at 390 nm without any new band at the end of the spectrum, even at higher concentrations and lower temperatures. The main reason for the absence of aggregate formation in PFO-2 is the sterical hindrance caused by the branched alkyl side chains. In addition, Density Functional Theory (DFT) was used to compute the HOMO–LUMO transitions, electron charge distribution, and frontier molecular orbitals for each polymer. The Mulliken charge distribution and demonstrated a notable difference in the reactivity of the alkyl side chain, confirming the higher ability of PFO-1 to form CH-π bonds. docking model emphasized that the band at 437 nm could be attributed to the interaction between CH in the n-alkyl side chain and π bonds in the aromatic rings of PFO-1.

Molecular Structure, Spectroscopic Investigation, Docking and in Vitro Cytotoxicity Studies of 7-Methoxycoumarin as anti-Leukemia Agent

The vibrational assignments of 7-methoxycoumarin (7MC), a potential anticancer agent, have been studied by the experimental (FTIR and FT-Raman) and theoretical methods. The density functional theory DFT- B3LYP technique with cc-pVTZ basis set is utilized to examine the molecular geometry, electrostatic potential (MEP), infrared intensities, Raman activities, Mulliken charge and thermodynamic limits. The molecular charge exchange in orbitals has been examined by natural bond orbital (NBO) analysis. HOMO-LUMO transition and the UV absorption by using TD-DFT approach have been investigated. The molecular docking studies have been executed for interaction of 7MC with the sites of human Bruton tyrosine kinase (BTK), Phosphoinositide 3'-kinase (PI3K) and Spleen Associated Tyrosine Kinase (SYK). MTT assay is used to study the anticancer activity of 7MC through five human cancer cell lines (A-549, HEPG2, HEp2, MCF-7, and HL-60). The results suggested that the 7MC can have possibly been used as an agent of anti-leukemia efficacy.

MagnetoPlasmonic Waves/HOMO-LUMO Free π-Electron Transitions Coupling in Organic Macrocycles and Their Effect in Sensing Applications

Optical and magneto-optical surface plasmon resonance (MOSPR) characterization and preliminary sensing test onto single- and multi-layers of two organic macrocycles have been performed; TbPc2(OC11H21)8 phthalocyanine and CoCoPo2 porphyrin were deposited by the Langmuir-Schäfer (LS) technique onto proper Au/Co/Au magneto-optical transducers. Investigations of the MOSPR properties in Kretschmann configuration by angular modulation, gives us an indication about the potential discrimination of two organic macrocycles with absorption electronic transition in and out of the propagating plasmon energy spectral range. An improved molecular vapors sensitivity increase by the MOSPR sensing probe can be demonstrated depending on the overlap between the plasmonic probe energy and the absorption electronic transitions of the macrocycles under investigation. If the interaction between the plasmon energy and molecular HOMO-LUMO transition is preserved, a variation in the complex refractive index takes place. Under this condition, the magneto-plasmonic effect reported as 1/|MOSPR| signal allows us to increase the detection of molecules deposited onto the plasmonic transducer and their gas sensing capacity. The detection mechanism appears strongly enhanced if the Plasmon Wave/HOMO-LUMO transitions energy are in resonance. Under coupling conditions, a different volatile organic compounds (VOC) sensing capability has been demonstrated using n-butylamine as the trial molecule.

The synthesis and characterization of ylideneisoindolinones

1,3-Diiminoisoindoline (DII) and the closely related molecule, iminoisoindolinone are important precursors in the synthesis of macrocycles and chelates such as phthalocyanines, and bis(arylimino)isoindolines, as well as chromophores including aza-BODIPY dyes. A series of seven ylideneisoindolinones are presented in this report. The reaction of various organic CH acids and iminoisoindolinone produce compounds that show strong [Formula: see text]* transitions in the UV region. The chromophores have been characterized spectroscopically and the X-ray structures show electronic delocalization across the chromophore. Additionally, DFT and time-dependent DFT calculations confirm the lower energy absorbances are primarily HOMO-LUMO transitions.

Antiaromatic 1,5-Diaza-s-indacenes.

s-Indacene is a classical non-alternant hydrocarbon that contains 12 π-electrons in a cyclic π-conjugation system. Herein, we report its nitrogen-doped analogue, 1,5-diaza-s-indacene. 1,5-Diaza-s-indacenes were readily prepared from commercially available 2,5-dichlorobenzene-1,4-diamine through a two-step transformation consisting of a palladium-catalyzed Larock cyclization with diaryl acetylenes followed by hydrogen abstraction. The thus obtained 1,5-diaza-s-indacenes exhibited distinct antiaromaticity, as manifested in clear bond-length alternation, a forbidden HOMO-LUMO transition, and a paratropic ring current. As compared to the parent s-indacene, the 1,5-diaza-s-indacenes showed higher electron-accepting ability owing to the presence of imine-type nitrogen atoms. The 1,5-diaza-s-indacene core is effectively conjugated with the peripheral aryl groups, which enables fine-tuning of the absorption spectra and redox properties. The two possible localized forms of 1,5-diaza-s-indacene were compared in terms of their energetic aspects.

Antiaromatic 1,5‐Diaza‐s‐indacenes

Abstracts‐Indacene is a classical non‐alternant hydrocarbon that contains 12 π‐electrons in a cyclic π‐conjugation system. Herein, we report its nitrogen‐doped analogue, 1,5‐diaza‐s‐indacene. 1,5‐Diaza‐s‐indacenes were readily prepared from commercially available 2,5‐dichlorobenzene‐1,4‐diamine through a two‐step transformation consisting of a palladium‐catalyzed Larock cyclization with diaryl acetylenes followed by hydrogen abstraction. The thus obtained 1,5‐diaza‐s‐indacenes exhibited distinct antiaromaticity, as manifested in clear bond‐length alternation, a forbidden HOMO–LUMO transition, and a paratropic ring current. As compared to the parent s‐indacene, the 1,5‐diaza‐s‐indacenes showed higher electron‐accepting ability owing to the presence of imine‐type nitrogen atoms. The 1,5‐diaza‐s‐indacene core is effectively conjugated with the peripheral aryl groups, which enables fine‐tuning of the absorption spectra and redox properties. The two possible localized forms of 1,5‐diaza‐s‐indacene were compared in terms of their energetic aspects.

Synthesis and Physical Properties of Trioxotriangulene Having Methoxy and Hydroxy Groups at α-Positions: Electronic and Steric Effects of Substituent Groups and Intramolecular Hydrogen Bonds.

New 4,8,12-trioxotriangulene (TOT) neutral radical derivatives having three methoxy and hydroxy groups at the α-positions were synthesized, and the substituent effects on the electronic spin and redox properties were elucidated in the theoretical and experimental methods. Due to the small SOMO coefficients at the α-positions of TOT, the methoxy groups in the TOT neutral radical had negligible effects on the electronic spin structure and redox ability. On the other hand, methoxy groups greatly increased the LUMO energy having large coefficients at α-positions and, thus, caused a remarkable negative-potential shift of the redox wave of anion species involving the dianion and trianion species. Converting the methoxy groups to hydroxy groups caused a dramatic change in the electronic structure of TOT, where the intramolecular hydrogen bonds between hydroxy groups and oxo groups strongly attracted a minus charge on the TOT skeleton. The HOMO energy of the monoanion species was significantly reduced, causing a blue shift of the HOMO-LUMO transition and an anodic shift of the redox potential. In addition, due to the steric repulsion smaller than that of the methoxy group, the hydroxy derivative showed a more planar molecular structure and a strong π-stacking ability.

Synthesis, spectral, stereochemical, biological, molecular docking and DFT studies of 3-alkyl/3,5-dialkyl-2r,6c-di(naphthyl)piperidin-4-one picrates derivatives

A new series of 3-alkyl/3,5-dialkyl-2r,6c-di(naphthyl)piperidin-4-one picrates (1-6) were synthesized their chemical structures were confirmed by elemental analysis, FT-IR, 1H and 13C NMR and mass spectral techniques and for compound 4 was characterized by HOMOCOSY, HSQC, HMBC, NOESY, and DEPT NMR spectral techniques. From the NMR spectral data, the observed chemical shifts and coupling constants suggested that compounds (1-6) adopt a normal chair conformation with equatorial orientation of all the naphthyl groups at C-2 and C-6 and alkyl group at C-3 and C-5 and from the 1H chemical shifts H-5a and H-3a have a higher magnitude than H-5e. This is due to 1,3 diaxial interaction between axial NH proton and axial protons at C-3 and C-5. The synthesized compounds were screened for their bacterial activity against Escherichia coli, Staphylococcus aureus, Bacillus.subtilis, Vibreo cholerae and Pseudomonas aeruginosa and fungal activity against Candida albicans, Aspergillus niger, Aspergillus flavus and Trichophyton rubrum. All the compounds showed good antibacterial and antifungal activities. The optimized molecular structure of the synthesized compounds (1-6) were studied by using DFT/B3LYP/6-311++G(d,p) basis set. The calculated electrical dipole moment (µ) and first hyperpolarizability (βo) values shows that all the molecules might have nonlinear optical (NLO) behavior. The HOMO-LUMO transition implies that intra-molecular charge transfer takes place within the molecule. Molecular electrostatic potential (MEP) surface is used to understand the reactive sites of a molecule. To establish information about the molecular interactions between protein and this novel compound theoretically, docking studies were carried out in detail.

Optically Controlled Electron Transfer in a ReI Complex.

Ultrafast optical control of intramolecular charge flow was demonstrated, which paves the way for photocurrent modulation and switching with a highly wavelength-selective ON/OFF ratio. The system that was explored is a fac-[Re(CO)3 (TTF-DPPZ)Cl] complex, where TTF-DPPZ=4',5'-bis(propylthio)tetrathiafulvenyl[i]dipyrido[3,2-a:2',3'-c]phenazine. DFT calculations and AC-Stark spectroscopy confirmed the presence of two distinct optically active charge-transfer processes, namely a metal-to-ligand charge transfer (MLCT) and an intra-ligand charge transfer (ILCT). Ultrafast transient absorption measurements showed that the ILCT state decays in the ps regime. Upon excitation to the MLCT state, only a long-lived 3 MLCT state was observed after 80 ps. Remarkably, however, the bleaching of the ILCT absorption band remained as a result of the effective inhibition of the HOMO-LUMO transition.

SPECTRAL, STRUCTURAL, STABILITY CHARACTERISTICS AND FRONTIER MOLECULAR ORBITALS OF TRI-N-BUTYL PHOSPHATE (TBP) AND ITS DEGRADATION PRODUCTS: DFT CALCULATIONS

This work demonstrates the facilities offered by density functional theory (DFT) to calculate the molecular structural and spectral properties of tri-n-butyl phosphate (TBP) and its derivatives, namely, di-n-butyl phosphate (HDBP) and mono-n-butyl phosphate (H2MBP). The computed parameters including frontier molecular orbitals and HOMOLUMO transitions indicated the TBP has the lowermost total energy with a lager HOMOLUMO energy bandgap followed by HDBP and H2MBP. These outcomes in terms of reactivity and stability were reversed counting their dipole moments. The simulated spectra of FTIR and Raman suggested these techniques could be considered as powerful for qualitative analysis of these compounds.

Chiroptical Properties of Indolenine Squaraines with a Stereogenic Center at Close Proximity.

A series of four indolenine squaraines bearing a chiral center at the 3-position of the indolenine moiety, with either an n-propyl or a phenyl group alongside a methyl group, were synthesized and obtained in a high purity of ≥98% for the desired stereoisomer. The indolenine precursors with a phenyl group attached at the chiral center were asymmetrically synthesized using a pericyclic-reaction cascade and obtained in a high ee of 98%, whereas the ones with an n-propyl group were prepared by kinetic resolution through asymmetric hydrogenation, resulting in an ee of up to 98%. X-ray crystallography revealed a slightly twisted geometry for the phenyl-substituted cisoid squaraine derivative, whereas the n-propyl-substituted derivative possessed the expected planar geometry. Variation of the substitution also influenced the optical properties, where the introduction of phenyl groups caused a progressive red-shift and reduction in squared transition moments, as well as reduced fluorescence quantum yields, Stokes shifts, and fluorescence lifetimes. All of the investigated compounds exhibited strong ECD signals, with Δε values of up to 24 M-1 cm-1 for the HOMO-LUMO transition. DFT calculations indicated that this was due to both large electric and magnetic transition moments, although the two vectors were mutually almost orthogonal.

Solvatochromism of dyes inspired in Effenberger's probe

Solvatochromic dyes have been utilized in recent decades as probes to measure the polarity of the medium. An interesting example is the Effenberger's dye (ED), which exhibits a very pronounced positive solvatochromism, being considered a dye that probes practically only the polarizability and dipolarity of the medium. This compound is difficult to be accessed and, in addition, the synthesis of dyes capable to probe the polarizability of the medium is a subject of interest. In view of this, six imine probes inspired in the molecular structure of ED were synthesized and characterized. Two compounds were solvatochromic and exhibit different colors in various solvents, while the other dyes exhibit a weak solvatochromism. Three probes present a behavior very similar to ED, showing a positive solvatochromic behavior. The application of multiparametric equations shows that polarizability is the most influential solvent parameter in the solvation of the dyes studied. Theoretical calculations were performed with a dye in ten different solvents, employing a continuum model to mimic solvent effects and TD/DFT calculations with two functionals exhibiting a different degree of Hartree–Fock exchange to estimate transition energy (ET) values. A HOMO–LUMO transition involving an internal charge transfer from the N,N–dimethylaminophenyl electron–donor to the nitrothienyl electron–acceptor moieties of the dye was identified as the origin of the solvatochromic band. The calculated ET values reproduce qualitatively the positive solvatochromism of the dye. The results obtained show that the easy synthesis of solvatochromic compounds, inspired in the ED, represents an interesting possibility in the research for novel polarizability probes.

Ultrafast Dynamics of the Two Lowest Bright Excited States of Cytosine and 1-Methylcytosine: A Quantum Dynamical Study.

The nonadiabatic quantum dynamics (QD) of cytosine and 1-methylcytosine in the gas phase is simulated for 250 fs after a photoexcitation to one of the first two bright states. The nuclear wavepacket is propagated on the coupled diabatic potential energy surfaces of the lowest seven excited states, including ππ*, nπ*, and Rydberg states along all the vibrational degrees of freedom. We focus in particular on the interplay between the bright and the dark nπ* states, not considering the decay to the ground electronic state. To run these simulations, we implemented an automatic general procedure to parametrize linear vibronic coupling (LVC) models with time-dependent density functional theory (DFT) computations and interfaced it with Gaussian package. The wavepacket was propagated with the multilayer version of the multiconfigurational time dependent Hartree method. Two different density functionals, PBE0 and CAM-B3LYP, which provide a different description of the relative stability of the lowest energy dark states, were used to parametrize the LVC Hamiltonian. Part of the photoexcited population on lowest HOMO-LUMO transition (πHπL*) decays within less than 100 fs to a nπ* state which mainly involves a promotion of an electron from the oxygen lone pair to the LUMO (nOπL*). The population of the second ππ* state decays almost completely, in <100 fs, not only to πHπL* and to nOπL* states but also to another nπL* state involving the nitrogen lone pair. The efficiency of the adopted protocol allowed us to check the accuracy of the predictions by repeating the QD simulations with different LVC Hamiltonians parametrized either at the ground-state minimum or at stationary structures of different relevant excited states.

Fluorescent 2-phenyl-2H-benzotriazole dyes with intramolecular N–H···N hydrogen bonding: Synthesis and modulation of fluorescence properties by proton-donating substituents

A series of 2-(2-phenyl)benzotriazole derivatives having amino, N-methyl amino, and acetamido groups on the ortho position of the phenyl group were synthesized to elucidate the effects of amino/amido substitutions on the molecular structures and photophysical properties. 1H NMR spectra and DFT calculations of the present dyes revealed the formation of N–H∙∙∙N intramolecular hydrogen bonds between benzotriazole and amino/amide groups in the ground state. Amino-functionalized dyes showed absorption bands that were assigned to HOMO-LUMO transition with a partial charge-transfer feature. The dye with an acetoamido group in which the acidity of NH proton was increased by the effect of electron-withdrawing acetyl groups exhibited absorption bands attributable to intramolecular hydrogen-bonded “closed” conformers in CHCl3 and non-hydrogen-bonded “open” conformers in DMSO. In comparison to 2-phenylbenzotriazole, which had no acidic proton involved in intramolecular hydrogen bonding, the present derivatives exhibited weak fluorescence emissions with quite low quantum yields, suggesting that non-radiative deactivation of ESIPT states also operated in the N–H∙∙∙N hydrogen bonded 2-phenylbenzotriazoles just as in O–H∙∙∙N intramolecular hydrogen-bonded 2-hydroxyphenylbenzotriazoles, which are known as UV absorbers. Taking a closer look at the fluorescence spectra, dyes with amino and N-methylamino groups showed faint but dual emissions from charge-transfer excited states in CHCl3 and blue-shifted single emission in DMSO. Fluorescence emissions of the acetamido-functionalized dye were unimodal in each solvent and stronger than those of amino-functionalized dyes. Thus, the fluorescence properties of these dyes depended on substitutions at amino groups. The luminescence of these derivatives was enhanced in the polymer matrix in which conformation changes and molecular motions were suppressed. Dye-doped polymer films have absorption bands in the UV range (360–400 nm) and emitted at the visible region (450–510 nm), and thus could be used as organic materials for light conversion films that convert UV light into visible light.

(4n +2)π Huckel’s rule of Bn NnC(8-2n) H8 as anti-cancer heterocyclic systems

Replacing of Boron and nitrogen atoms in [8] annulene molecule help us for explaining the details of mentioned magnetic mechanism concerning the ring currents of the carbon disappearing in the isoelectronic azabora-hetero-cycles variants (Bn Nn C(8-2n) H82-,n=0,1,2,3 and4 The (4n+2)π systems aromatic on variants of BnNnC(8-2n) H8 (n=0, 1 ,2,3 and 4) via the localized orbital by considering the current density induced have been studied. It has been predicted a four-electron dia-tropic (aromatic) ring current for (4n+2) π aza-bora-hetero-cycles variants of BnNnC (8-2n) H8(n=0,1 ,2,4) and a two-electron para-tropic (anti-aromatic) current for (4n) π. HOMO and LUMO energies and also HOMO/LUMO overlapping in whole space have been calculated. Two forms can be considered, first the HOMO–LUMO transition leads to a para-tropic contribution, and second HOMO–LUMO+1 transitions to the dia-tropic contributions. In addition, the NICS and SNICS values confirm the amounts of aromaticity and anti-aromaticity in those rings.

Thiolato Protected Copper Sulfide Cluster with the Tentative Composition Cu74S15(2-PET)45.

Ligand protected copper nanoclusters with precise compositions have attracted considerable attention due to their unique photoluminescent properties. However, the acquisition of structural information, knowledge of the factors affecting the stability, and high quantum yields are prerequisites for assessing their applications in biomedicine as fluorescent contrast agents, biosensors, and probes for cells. Despite all the effort, only finite examples of single crystal structures of CuNCs are reported. Herein, we report the phosphine-free synthesis and structure determination of 2-PET protected CuNCs. The structure analysis established by single crystal X-ray diffraction reveals the formation of binary Cu74S15(2-PET)45 sulfide cluster. A similar phenomenon has been observed for several other chalcogenide-bridged copper clusters. The synthesized cluster possesses a rod-like structure, protected with 45 thiol ligands on the surface. Fifteen independent bridged-sulfur atoms couple to the copper atoms inside the core. Calculations for both a neutral and negatively charged cluster showed no major differences in their geometrical structures. Further analysis of frontier MO levels of the closed-shell anion predicts the HOMO-LUMO transition to be intramolecular L7 → L1 charge transfer, where "L7" and "L1" abbreviations refer to the corresponding sulfur layer in the structure. For the neutral cluster, the calculated spin density is delocalized over the two moieties. On the basis of TDDFT+TB calculations, the onset of the measured absorption spectrum could be satisfactorily reproduced.

Dye Aggregation, Photostructural Reorganization and Multiple Concurrent Dye···TiO2 Binding Modes in Dye-Sensitized Solar Cell Working Electrodes Containing Benzothiadiazole-Based Dye RK-1

Dye-sensitized solar cells (DSSCs) are widely considered to be promising contenders for the next generation of photovoltaic devices. The light-harvesting component in the DSSCs, that is, the sensitizers, are adsorbed onto the semiconductor layer to form the photoelectrode that absorbs solar energy and converts it into electrical power. The choice of dye has a profound impact on the DSSC performance. Thus, substantial research efforts have been devoted to the development and testing of a large variety of sensitizers during the past decades. We, herein, focus our attention on the metal-free benzothiadiazole-based dye, 2-cyano-3-(4-(7-(5-(4-(diphenylamino)phenyl)-4-octylthiophen-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)phenyl) acrylic acid (RK-1), which exhibits excellent power conversion efficiency and high stability. Simulations and experiments were combined to conduct a systematic study of its optical and structural properties. RK-1 shows a broad absorption band over the visible region and the formation of H aggregates in solution. Deprotonation of the cyanoacrylic acid group in RK-1 occurs upon dye adsorption onto TiO2. This induces a hypsochromic shift of the absorption band. The emission spectrum of RK-1 shows a broad band and a large Stokes shift (6949 cm–1), indicating the presence of several different structural reorganization processes during excitation. Time-dependent density functional theory (TD-DFT) calculations reveal that intramolecular charge transfer in RK-1 molecules should be predominantly attributed to the HOMO–LUMO transition. DFT modeling also reveals the involvement of the cyano group of RK-1 in anchoring to TiO2, which makes the dye···TiO2 binding structure more stable. Fourier transform infrared spectroscopy data prove that bridging bidentate (BB) and COO/CN (A2) binding modes coexist in the RK-1···TiO2 interfacial structure.