Search

Comparative study of nonlinear optical properties of red fluorescent coumarins was carried out with density functional theory based ab initio method using the popular global hybrid (GH) and range separated hybrid (RSH) functionals and correlated with the spectroscopic values. The GHs - M06 L, PBE1PBE, M06, BHHLYP, M062X and M06HF and RSHs - HISSbPBE, wB97, wB97X, HSEH1PBE, CAM-B3LYP and wB97XD in combination with the double zeta basis function 6-311 + G(d,p) were used. The computed polarizability (α 0 ), hyperpolarizability of the first order (β 0 ) and second order (γ) computed by the RSHs are closer to the spectroscopic values compared to GHs. Polarizabilities computed with the functionals BHHLYP and M06-2X are closer with the spectroscopic values. Incorporation of additional cyano group enhances the NLO response. An increase in electrophilic nature contributed from the reduced orbital band gap culminating an increase in α 0 , β 0 , and γ in all the cases. The NLO response was found to be highly solvent dependent that is the polarity of the micro environment created by the solvents. To understand the agreement and accuracy among the NLO parameters obtained from the selected DFT functionals and the spectroscopic values, the mean absolute error (MAE) and vibrational contribution parameters are presented. Two photon absorption (TPA) cross section depends upon the molecular structure where π-framework is an important factor rather than number of acceptors.

Density functional theory and time-dependent density functional theory computations were used to understand the electronic and photophysical parameters of NIR β-thiophene-fused BF 2 -azadipyrromethene dyes. The computed data are in good agreement with those obtained experimentally and they provide insights into the origin of red shifted optical spectra compared to the parent aza-BODIPY, low Stokes shift, non-linear optical responses and quantitative description of the singlet-triplet energy gap. The resultant decrease in the HOMO - LUMO energy gap is responsible for the red shift. The possible use as non-linear optical materials is supported by large enhancement in the non-linear optical properties. On the basis of vertical triplet energies, their possible potential therapeutic use as a photosensitizer in photodynamic therapy is proposed. The singlet-triplet energetic gaps suggest that the β-thiophene-fused BF 2 -azadipyrromethene dyes can act as a sensitizer to produce an efficient generation of singlet oxygen. Their optimal use as an efficient singlet fission materials has been proposed on the basis of excitation energies in the ground, lowest singlet and triplet excited states.

The electronic structures and spectroscopic properties of triphenylamine-based monostyryl and bis(styryl) dyes were studied using quantum chemical methods. The ground-state geometries of these dyes were optimized using the density functional theory (DFT) method. The lowest singlet excited state was optimized using time-dependent density functional theory (TD-DFT). The absorption was also calculated using the ground-state geometries. All the calculations were carried out in the gas phase and in solvent. The results indicate that the absorption maxima calculated using the TD-DFT are in good agreement with those obtained experimentally. These dyes possess a large second-order non-linear property and this is mainly due to the strong donor-π-acceptor conjugation which is attributed to the excited state intramolecular charge transfer (ICT). There is a relationship between the hardness and first hyperpolarizability and second hyperpolarizability of mono- and bis(styryl) dyes. The efficiency of the intersystem crossing process can be improved by reducing the energy gap between the singlet and triplet excited states.

The 2,2'-dinaphtholazobenzene molecular framework (P) was designed, synthesized and characterized. Its absorption and fluorescence properties revealed that P is a dual sensor for copper ions (Cu 2+ ) and fluoride ions (F - ) in DMSO. The colorimetric activities were clearly visible by naked eye upon the addition of the two ions. Fluorescence quenching and enhancement were observed when Cu 2+ and F - ions were added respectively. Density Functional Theory (DFT) calculations were carried out to provide an insight into the interaction of guest ions (Cu 2+ and F - ) with P, and to explain how the molecular orbitals were affected. Graphical Abstract ᅟ.

Hanson et al. [Org. Lett., 2011] reported the absorption and emission spectrum of 5,6-dichloro-1,3-bis(2-pyridylimino)-4,7-dihydroxyisoindole but the excited-state intramolecular proton transfer (ESIPT) process was not investigated. The photo-physical behaviour of 5,6-dichloro-1,3-bis(2-pyridylimino)-4,7-dihydroxyisoindole was studied using the density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The functional used was B3LYP and 6-31G(d) was the basis set for all the atoms. All the ten tautomers were studied for the absorption and emission properties. It is found that the tautomer where hydroxyl groups are syn to nitrogen of isoindoline ring is most stable and thus, responsible for the ESIPT process. The computed absorption and emission values of tautomers using TD-DFT are in good agreement with those obtained experimentally.

The photo-physical behaviour of bis-2,5-(2-benzoxazolyl) hydroquinone and 2,5-bis (benzo[d]oxazol-2-yl)-4-methoxyphenol was studied using the Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT). All the possible rotamers were optimized to obtain global minimum optimized structure. The theoretical absorption and emission values of rotamers estimated by using TD-DFT [TD-B3LYP/6-31G(d)] are in good agreement with experimental absorption and emission wavelengths. Based on the absorption values, the contribution of respective rotamer is determined theoretically.

Red emitting dyes are of interest in various technological applications. Coumarins, though being an important class of fluorescent molecules, those with red emission, have been rarely studied theoretically. The structural and electronic aspects of three novel red emitting coumarins were studied using DFT and TD-DFT methods. The functionals employed were the hybrid functionals B3LYP, CAM-B3LYP, PBE0 and the highly parameterized empirical functional M06. The geometry at ground state reveals the electron donor N,N-diethylamino group is coplanar with the chromophoric system and the nitrile group induces a red shift to the absorption and emission. The electronic energies and dipole moments were solvent dependent. The basis sets and functionals were benchmarked for their performance with these molecules. B3LYP has been proved to be more efficient in computations whereas the basis sets do not have noticeable effect on the electronic properties. However, adding a polarization function to the basis set has improved the calculation of vertical excitation. The B3LYP functional gives maximum absolute deviation of 0.20 eV in calculating the vertical excitations and 0.18 eV for emission.

The photophysical and electrochemical properties of eleven polycyclic benzimidazole fused organic pigments (four based on phthalic anhydride, four based on naphthalic anhydride and three based naphthalene tetra carboxylic acid dianhydride) were investigated using density functional theory and time dependent density functional theory methods (B3LYP/6-31G(d) and M06/6-31G(d)). The predicted geometries are comparable using both functionals. The electrochemical properties are in good agreement with the experimental results. However, the experimental absorption-emission properties are closer to the values computed using the M06/6-31G(d) method. Both the methods perform equally well in explaining the intramolecular charge transfer characteristics. This work can help to understand the modern age functional materials at molecular level and to design new molecules.