Effect of structural changes in sesquifulvalene on the intramolecular charge transfer and nonlinear polarizations – a theoretical study

Synthesis, molecular, electronic structure, linear and non-linear optical and phototransient properties of 8-methyl-1,2-dihydro-4H-chromeno[2,3-b]quinoline-4,6(3H)-dione (MDCQD): Experimental and DFT investigations

Base catalysed ring opening ring closure (RORC) reaction of 6-methylchromone-3‑carbonitrile (1) with 1,3-cyclohexanedione afforded 8-methyl-1,2-dihydro-4H-chromeno[2,3-b]quinoline-4,6(3H)-dione (MDCQD). Theoretical calculations by Density Functional Theory (DFT) at the B3LYP/6-311G (d,p) level of theory was utilized to illustrate the equilibrium geometries of MDCQD. Also, the nonlinear optical properties, simple harmonic vibrational frequencies, thermo-chemical parameters and Mullikan atomic charges were calculated. In addition, the electronic absorption spectra in polar and non polar solvents were discussed on the basis of TD-DFT calculations. A nanofiber-like structure with high aggregation was resolved by using scanning electron microscopy images and its particle sizes were measured by particle size analyzer. The spectroscopic characteristics of the prepared thin film of MDCQD were studied in a wide spectral range of 200-2500nm. The analysis of the absorption edges affords two direct optical band gaps with energies of 1.00 and 2.76eV. A characteristic emission peak of photoluminescence spectrum in the visible region was detected and has a red-shift as a result of solvent polarity. The MDCQD film based heterojunction showed rectification behavior and diode-like characteristics. The photovoltaic characteristics under illumination of 100mW/cm² were studied. The open-circuit voltage and short-circuit current were found to be 0.22V and 4.25×10^-7A/cm², respectively. Moreover, the prepared heterojunction showed remarkable phototransient characteristics which afford the probability for the operation as a photodiode.

Twisted intramolecular charge transfer and its contribution to the NLO activity of Diglycine Picrate: a vibrational spectroscopic study

Single crystals of Diglycine Picrate (DGLP) were grown by slow evaporation technique and the vibrational spectral analysis is carried out using FT Raman and FT-IR spectroscopy, supported by Density Functional Theoretical (DFT) computations to derive equilibrium geometry, vibrational wavenumbers and first hyperpolarizability. The vibrational spectra confirm the existence of NH3(+) in DGLP. The influence of Twisted Intramolecular Charge Transfer (TICT) caused by the strong ionic ground state hydrogen bonding between charged species making DGLP crystal to have the non-centrosymmetric structure has been discussed. The Natural Bond Orbital (NBO) analysis confirms the occurrence of strong intermolecular N-H⋯O hydrogen bond. The HOMO-LUMO energy gap and the first order hyperpolarizability were calculated and it supports the nonlinear optical activity of the Diglycine Picrate crystal.

Non linear optical analyses of hexamine: phenol cocrystals based on hydrogen bonding: a comparative study

Fourier-Transform Infrared (FT-IR) spectroscopy supported by Raman spectroscopy has been employed to explain the conventional and unconventional hydrogen bonding present in the 4,4'thiodiphenol: hexamine and 4,4'sulfonyldiphenol: hexamine cocrystals. The possible internal and external vibrational modes are predicted through factor group analysis. Influence of intra molecular charge transfer (ICT) interaction caused by the strong ionic ground state hydrogen bonding between charged species, giving rise to a non centro symmetric structure which is a criterion for second harmonic generation (SHG) efficiency has been discussed. Intense low wave number hydrogen bond vibrations in Raman which arise due to electron-phonon coupling are analyzed. Optical quality of adducts is identified through UV-Vis analysis. The second harmonic generation efficiency of both adducts is determined by Kurtz-Perry method.

NLO and NBO Analysis of Sarcosine-Maleic Acid by Using HF and B3LYP Calculations

We report a theoretical study on molecular structure, vibrational spectra, nonlinear optical (NLO), and natural bond orbital (NBO) analysis of sarcosine-maleic acid (C7H11NO6) in the ground state calculated by using the Hartree-Fock (HF) and density functional method (DFT/B3LYP) with 6–31++G(d,p) basis set. We repeat NBO calculations with 6–31G(d,p) basis set so as to see the diffuse function impact on NBO analysis. Stability of the molecule arising from hyper conjugative interactions and charge delocalization has been analyzed using NBO analysis. NBO analysis shows that there is a O–H⋯O and N–H⋯O hydrogen bond in the title compound, which is consistent with the conclusion obtained by the analysis of molecular structure. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. Also, these results are supported by the NLO parameters. Finally, the calculated results were applied to simulate infrared and Raman spectra of the title compound which showed good agreement with experimental ones.

Second and third-order nonlinear optical properties and molecular parameters of azo chromophores: semiempirical analysis

The static and frequency dependent average polarizability (<α>), first- and second-hyperpolarizabilities (<β> and <γ>) and highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LUMO) energies of nonlinear optical chromophores with nitro acceptors 1-5 have been investigated by using the Austin Model 1 (AM1), Modified Neglect of Diatomic Overlap (MNDO), MNDO with d orbitals (MNDO-d), Parameterization Method 3 (PM3), Recife Model 1 (RM1) and Parameterization Method 6 (PM6) methods within a time-dependent Hartree-Fock (TDHF) approaches. The electronic properties of chromophores 1-5 have been reported by employing two-state model calculated at Zerner's spectroscopic version of the Intermediate Neglect of Differential Overlap singly excited configuration interaction (ZINDO/S-SCI) method. Also, the molecular hardness (η) and electronegativity (χ) parameters have been obtained by using molecular frontier orbital energies. The <α>, <β>, <γ> HOMO, LUMO energies, η and χ parameters have been investigated with respect to the choice of different semiempirical methods.

Natural bond orbital analysis, electronic structure, non-linear properties and vibrational spectral analysis of L-histidinium bromide monohydrate: a density functional theory

The spectroscopic properties of the crystallized nonlinear optical molecule L-histidinium bromide monohydrate (abbreviated as L-HBr-mh) have been recorded and analyzed by FT-IR, FT-Raman and UV techniques. The equilibrium geometry, vibrational wavenumbers and the first order hyperpolarizability of the crystal were calculated with the help of density functional theory computations. The optimized geometric bond lengths and bond angles obtained by using DFT (B3LYP/6-311++G(d,p)) show good agreement with the experimental data. The complete assignments of fundamental vibrations were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The natural bond orbital (NBO) analysis confirms the occurrence of strong intra and intermolecular N-H⋯O hydrogen bonding.

The consistency analysis of different semiempirical calculations on second- and third-order nonlinear optical properties of donor-acceptor chromophores containing alpha-cyan

The static and frequency dependent average polarizability (<alpha>), first- and second-hyperpolarizabilities (<beta> and <gamma>) and HOMO and LUMO energies of donor-acceptor chromophores containing alpha-cyan (1a-c) have been investigated by using the AM1, MNDO, MNDO-d, PM3, RM1 and PM6 methods within a time-dependent Hartree-Fock (TDHF) approaches. The electronic properties of 1a-c have been reported by employing two-state model calculated at ZINDO/S-SCI, PM3-SCI and RM1-SCI methods. Also, the molecular hardness (eta) and electronegativity (chi) parameters have been obtained by using molecular frontier orbital energies. The <alpha>, <beta>, <gamma> HOMO, LUMO energies, eta and chi parameters have been investigated with respect to the choice of different semiempirical methods. The variation graphics of beta, beta(0), eta and chi parameters according to the different semiempirical methods are presented. Furthermore, the variation graphics of beta(0) with regard to the mu(eg), Deltamu and lambda(eg) are displayed. The frontier molecular orbital and electrostatic potential pictures of 1a-c using ZINDO/S-SCI level have been examined. The results of 1a-c display significant second- and third-order molecular nonlinearity.

Electronic Structure and Spectroscopic Properties of the Two Structural Isomers of Donor−Acceptor Substituted Sesquifulvalene in the Gas and Solution PhasesA Case Study of Sudden Polarization

The ground state equilibrium structure and electric properties of two structural isomers of donor-acceptor substituted sesquifulvalene have been calculated at ab initio HF and MP2 levels for different conformations. The electronic properties of low lying excited singlets are calculated by using CI calculations including single excitations only. Isomer I in which the inter-ring charge transfer (CT) is reinforced in the presence of substituents shows sudden polarization in the ground and two lower lying excited states, while isomer II in which the longitudinal CT interaction is attenuated does not exhibit sudden polarization. The phenomenon of sudden polarization has been rationalized in terms of the easy polarization, smaller rotational barrier, and enhanced inter-ring CT on going from the planar to the orthogonal geometry. The appreciably large static second-order polarizability of I stems from its sudden polarized ground state. The solvent (using the conductor-like polarizable continuum model (CPCM)) plays a significant role on the modulation of ground and excited state electronic properties which, in general, predicts blue-shifts for I. However, for molecule II, the two lower energy transitions show a red-shift while the others show a weaker blue-shift at any conformation.

First Hyperpolarizability of a Sesquifulvalene Transition Metal Complex by Time-Dependent Density-Functional Theory

The first hyperpolarizability and electronic excitation spectrum of sesquifulvalene and a sesquifulvalene ruthenium complex have been computed and analyzed with use of time-dependent density-functional theory. A new orbital decomposition scheme is introduced that allows the computed first hyperpolarizability to be related to the electronic structure of complex molecules. The analysis shows that the first hyperpolarizability of sesquifulvalene is not associated with the first intense absorption, with HOMO-1 --> LUMO+1 character, but is dominated by the lowest energy transition, with HOMO --> LUMO character, despite its very low intensity. In the ruthenium complex, the analysis reveals that the strong enhancement of the nonlinear optical response compared to free sesquifulvalene should not be attributed to the effect of complexation on the hyperpolarizability of sesquifulvalene. The strong hyperpolarizability originates from MLCT transitions from ruthenium d-orbitals to an empty orbital located at the seven ring of sesquifulvalene, transitions that have no analogue in free sequifulvalene.

Substituent-Dependent Photoinduced Intramolecular Charge Transfer in N-Aryl-Substituted trans-4-Aminostilbenes

The photochemical behavior of trans-4-(N-arylamino)stilbene (1, aryl = 4-substituted phenyl) in solvents more polar than THF is strongly dependent on the substituent in the N-aryl group. This is attributed to the formation of a twisted intramolecular charge transfer (TICT) state for those with a methoxy (1OM), methoxycarbonyl (1CO), or cyano (1CN) substituent but not for those with a methyl (1Me), hydrogen (1H), chloro (1Cl), or trifluoromethyl (1CF) substituent. On the basis of the ring-bridged model compounds 3-6, the TICT states for 1CN and 1CO result from the twisting of the anilino-benzonitrilo C-N bond, but for 1OM it is from the twisting of the stilbenyl-anilino C-N bond, both of which are distinct from the TICT states previously proposed for N,N-dimethylaminostilbenes.