Enhanced quantum efficiency of dicyano BODIPYs over difluoro BODIPYs: A DFT approach.

The modified BODIPY (pyrromethene) dyes with cyano (-CN), substituting usual fluorine (-F), at the 4-position may give enhanced photochemical stability and quantum yield of fluorescence (QYF) when compared to the corresponding fluoro derivative. We have investigated and discussed comparatively the structural parameters of the ground (S0) and excited (S1) state geometries of a few widely used BODIPY dyes, both 4-cyano and 4-fluoro pyrromethene (PM), through DFT and TD-DFT studies and established the reasons for improved QYF of the cyano derivatives. The electrophilicity index indicates the stability of the excited geometry of the cyanated BODIPY and the calculated transition dipole moments reveal a longer lifetime of the excited state (S1) for the cyano BODIPY. The higher singlet and triplet gap in cyanated BODIPY accounts for higher QYF due to restricted transition from singlet to triplet state. This suggests that a population inversion, crucial for laser action, is easier to build up for cyano derivative than for the commonly used fluoro analogue while other gain/loss parameters of the PM dye lasers remain similar. Hence, 4-cyano derivatives of the PM dyes may be useful for more efficient lasing applications. The non-linear optical properties of the PM dyes are also investigated.

Exploration of 4-substituted thiophene-based azo dyes for dye-sensitized solar cells and non-linear optical materials: synthesis and an in silico approach.

This work examines the effects of changing the secondary donors' donating strengths at the thiophene ring's fourth position in a range of dyes designated SR1 to SR9. The DFT results indicate that the molecular planarity is greatly affected by the placement of the secondary donor at position four, which changes the charge transfer (CT) characteristics in the thiophene-azo-salicylic acid backbone. These results are corroborated by TD-DFT analysis, which indicates that as the secondary donor's donating strength increases, so does the vertical absorption maximum. Based on the computed photovoltaic characteristics, these dyes perform better from SR1 to SR5. Research on dye@TiO2 clusters suggests a potential for binding with TiO2, which might cause the dye@TiO2 clusters' absorbance to shift red. Additionally, computed linear and non-linear optical (NLO) properties exhibit similar trends to those observed for DSSC performance. The experimental results, which include HOMO and LUMO energies as well as initial absorption in dimethylformamide (DMF), match very well with the patterns seen in DFT and TD-DFT calculations. The high thermal stability of SR1 to SR4 is indicated by thermogravimetric analysis (TGA), indicating their practical applicability in non-linear optics (NLO) and DSSC applications. The efficiencies of the produced DSSCs vary; SR4 has the highest efficiency (4.50 ± 0.1), and SR1 has the lowest (0.37 ± 0.1). The combined effects of theoretical and experimental DSSC results demonstrate the vital role of secondary donors in influencing molecular characteristics and NLO and DSSC performance.

Effect of spirocyclization of xanthene dyes on linear and nonlinear optical properties by considering D-π-A and D-A-D Systems: DFT and TD-DFT approach.

Spirocyclization, a unique feature of xanthene dyes, makes it a promising candidate for developing fluorescent ratiometric probes for sensing, imaging, tracking, and labeling. How will this feature of xanthene dyes influence the linear and nonlinear optical properties? To examine the effect of spirocyclization of xanthene dyes, we have selected both the open-close form of rhodamine B and π-extended xanthene dyes substituted with thienyl and thieno[3,2-b]thienyl group at position 3 and 6. Here, rhodamine B will serve as the (Donor)D-π-A(Acceptor) system and thiophene-substituted xanthene dyes will serve as the D-A-D system. The geometry optimization of the close-open form of xanthene dyes at B3LYP/6-311++G(d,p) and CAM-B3LYP/6-311++G(d,p) revealed that the open form is energetically more stable in the S0 state than the closed form. The vertical excitation energy (ΔE), from Time-Dependent-Density Functional Theory (TD-DFT) calculation at B3LYP/6-311++G(d,p), CAM-B3LYP/6-311++G(d,p), ωB97XD/6-311++G(d,p) revealed that (ΔE)open < (ΔE)close. Further, the open form of xanthene dyes displays red-shifted absorption compared to the closed form. The λVt of xanthene dyes (open-close forms) is mainly assigned to HOMO â†’ LUMO transition (S0 â†’ S1) with % orbital contribution for open form âˆ¼ 90 % and close form âˆ¼ 60 %. The oscillator strength of xanthene dyes is obtained in the range of 0.01 - 1.74. The λVt of xanthene dyes is in agreement with experimental absorption. The static polarizability (α0), first-order hyperpolarizability (ß0), second-order hyperpolarizability (γ), molecular hyperpolarizability (µß0), and frequency-dependent hyperpolarizability (ß1064), of the open form of xanthene dyes, were found to be higher than the close form. Thus, the open form of xanthene dyes will show superior linear and nonlinear optical properties than the closed form. The thienyl[3, 2-b] thieno substituted xanthene dye with red-shifted absorption shows higher α0, ß0, γ, µß0, ß1064, and γ values, show better linear and NLO properties than thienyl and diethylamine substituted xanthene dyes.

A promising small-sized near-infrared absorbing zwitterionic dye for DSSC and NLO applications: DFT and TD-DFT approaches.

Herein we investigate three quinoid zwitterionic dye sensitizers having donor-donor (4-dimethylaniline; ZIDM), donor-acceptor (4-dimethylaniline and 4-benzoic acid; ZIMCA), and acceptor-acceptor (4-benzoic acid; ZIDCA) that can be used in dye sensitized-solar cells and non-linear optical (NLO) application through density-functional theory (DFT) and time-dependent-DFT computations. ZIDM showed better charge transfer than ZIMCA and ZIDCA, which showed similar trends in chemical potential, electrophilicity index, hardness, and hyperhardness. The higher values of open circuit voltage, light harvesting efficiency, lower binding, and adsorption energy values for the dye to bind with the TiO2 cluster were observed for ZIDM. The results suggest that these dyes can easily hold with the TiO2 cluster through the monodentate binding mode possible between Ti and oxygen of the zwitterionic backbone. The examination of the linear and NLO properties of these dyes revealed that ZIDM has a higher α0 = 80.64 × 10-24 esu, ß0 = 448.54 × 10-30 esu, and γ = 2219.23 × 10-36 esu in DCM. Similarly, higher values of molecular hyperpolarizability of 1335.0 × 10-48 esu and 8818.3 × 10-48 esu were observed in gas and DCM for ZIDM than ZIMCA and ZIDCA.

NLOphoric imidazole-fused fluorescent anthraquinone dyes.

The Z-scan and DFT techniques were explored to investigate the non-linear optical properties of anthraquinone fused imidazole-based D-π-A dyes. With the help of UV-visible spectral analysis, pH study, CV analysis, HOMO-LUMO interaction, MEP plots, and quinoidal character the influence of intramolecular charge transfer characteristics and H-bonding process on electronic and photophysical studies of anthraquinone derivatives were understood. The dyes 2-(4-(diethylamino)-2-hydroxyphenyl)-3H-anthra[1,2-d]imidazole-6,11-dione (AQ1) and 2-(2-hydroxynaphthalen-1-yl)-1H-anthra[1,2-d]imidazole-6,11-dione (AQ2) displayed a single emission with pronounced Stokes shift and thermal stability (upto 290 °C). The dye AQ1 exhibited strong charge transfer character which is explained by the ICT process leading to high nonlinear susceptibility χ(3) in AQ1 3.43 × 10-13 e.s.u relative to the dye AQ2 which has only ESIPT core. But, the dye AQ2 6.27 J cm-2 showed better optical limiting value. The NLO properties of AQ1 and AQ2 were computed by DFT functionals based on Hartree Fork (HF) percentage exchange. The dye AQ1 exhibits noticeable NLO properties. The global hybrid functionals with HF composition beyond 50% (BHHLYP, M06-HF) and the long rang corrected functionals (CAM-B3LYP, ωB97, and ωB97X) demonstrated comparable NLO properties relative to B3LYP and PBE0. It was observed that the combined effect of ICT and the H-bonding cores enhance the NLO properties. The experimental findings (Z-scan) were successfully correlated with theoretical (DFT) results.

Orange-Red Fluorescent (Partially Rigidified) Donor-π-(rigidified)-Acceptor System - Computational Studies.

D-π-A chromophore derived coumarins are studied using "DFT and TD-DFT" to compute vertical excitation as well as NLO properties using "global hybrid" (GH) functionals B3LYP and BHandHLYP and "range separated hybrid" (RSH) functionals CAM B3LY', wB97, wB97X, and wB97XD with basis set 6-311++G(d,p) and "correlation consistence polarized valence double and triple zeta" cc-pVDZ and cc-pVTZ respectively in the gas phase and two solvents, N,N-Dimethylformamide (DMF) and ethyl acetate (EA). The trends in absorption and emission values calculated by TD-DFT using all the above mentioned functional and basis sets were studied and it was observed that the trends seen in the computed parameters using B3LYP, BHandHLYP and CAM B3LYP are in good agreement with the trends in experimental values. DFT calculations were performed to determine "static dipole moment" (µ), "linear polarizability" (α), "first order hyperpolarizability" (ß0), "second order hyperpolarizability" (γ). We have calculated the mean average errors in dipole moment, linear polarizability, first and second hyperpolarizability and vertical excitation. We have observed large values of 'first order hyperpolarizability' (301-938 × 10^-30 e.s.u) and 'second order hyperpolarizability' (684-2498 × 10^-34) and they can act as good nonlinear optical materials. Also, vibrational contribution indicates the red shifted absorption and emission in 2c. They show higher values of electrophilicity index which indicates the stability and reactivity of molecules.

Red Emitting Hydroxybenzazole (HBX) Based Azo Dyes: Linear and Non Linear Optical Properties, Optical Limiting, Z Scan Analysis with DFT Assessments.

Herein, we report the hydroxybenzazole (HBX) containing azo dyes for "linear and non-linear optical" (NLO) applications. These bi-heterocyclic dyes have HBX scaffold (decorated with ESIPT core) and connected to another thiazole moietiy through azo bond. In DMF and DMSO, dyes are "emissive in yellow-red region" and "large Stokes shift" in the range of 62-121 nm were observed. "Nonlinear absorptive coefficient" (ß), "nonlinear refractive index" (ƞ2), "third order non-linear optical susceptibility" (χ3) in DMSO, ethanol and methanol were calculated using simple and effective "Z-scan technique" having "Nd: YAG laser" at 532 nm wavelength. 4.46 × 10-13 (e.s.u.) was the highest (χ3) was observed in DMSO among all the dyes. Optical Limiting (OL) values are in the range of 7.61-19.06 J cm-2 in solvents. Thermo Gravimetric Analysis (TGA) supports that, these compounds are useful for numerous high-temperature practices in the construction of electronic as well as optical devices. Band gap was calculated by CV as well as by DFT in acetonitrile. The same trend was observed when these HOMO-LUMO gaps were correlated in between CV and DFT. To gain more insights into structural parameters, molecular geometries were optimized at "B3LYP-6-311 + G (d,p)" level of theory. Further, "Molecular Electrostatic Potential" (MEP), "Frontier Molecular Orbitals" (FMO) were presented using "Density Functional Theory (DFT)". Global hybrid functional (B3LYP, BHandHLYP) and range separated hybrid functionals (RSH) i.e. CAM-B3LYP, ωB97, ωB97X, and ωB97XD were used to calculate linear and NLO properties. Graphical Abstract.

Benzothiazole-pyridone and benzothiazole-pyrazole clubbed emissive azo dyes and dyeing application on polyester fabric: UPF, biological, photophysical and fastness properties with correlative computational assessments.

Positional isomers of benzothiazole-pyridone and benzothiazole-pyrazole containing disperse azo dyes are reported. These heterocyclic azo dyes are decorated with 'separate ESIPT core' and show emission in seven solvents of different polarity. After application on polyester fabric, "very good to excellent" light and washing fastness properties were observed. Thermal stability of 'dyed fabric' was analysed by sublimation fastness test- and found 'very good to excellent' ratings at 210 °C. Ultraviolet Protection Factor (UPF) analysis of four 'dyed fabric' indicates the blocking 96-97% of UV radiation. Dyes were found effective on gram positive and negative bacteria by agar diffusion method and all the 'dyed fabrics' also showed more than 92% or 94% reduction of S. aureus or K. pneumoniae respectively by 'AATCC 100' method. Structures of the dyes were optimized using Density Functional Theory (DFT) to deduce stable tautomeric form. Calculated HOMO-LUMO gap is then compared with antibacterial activities. Electrophilicity index and lightfastness property were also compared and found to have very good correlation.

Schiff base clubbed benzothiazole: synthesis, potent antimicrobial and MCF-7 anticancer activity, DNA cleavage and computational study.

Schiff bases containing benzothiazole unit are synthesized and characterized by 1H NMR, 13C NMR, LC-MS, UV-visible and fluorescence spectroscopy methods. Synthesized compounds were evaluated for in vitro antibacterial activities on four different strains (Staphylococcus aureus, Bacillus sps, Escherichia. coli and Klebsiella pneumoniae) and antifungal activity on one strain (Candida albicans) by using 'micro-broth dilution method' (MIC in µg/mL). All compounds showed excellent antibacterial activity for S. aureus, E. coli and K. pneumoniae strains, as well as an antifungal activity for C. albicans, compared to standard Ciprofloxacin and Fluconazole, respectively. Molecular docking studies were carried out to get more insight into the binding mechanism. Reactivity of molecules was assessed using molecular electrostatic potential (MEP). HOMO-LUMO gap, chemical hardness and global softness were calculated and correlated with antimicrobial activity. VS5-e exhibits excellent antimicrobial activities and also shows more chemical reactivity and less toxicity which were confirmed by smaller HOMO-LUMO gap, lesser chemical hardness, higher global softness and lesser electrophilicity index. Henceforth, it was further assessed for DNA cleavage and against MCF-7 breast cancer cell. VS5-e reveals 85.82% inhibition of cancer cells at a concentration of 200 µg/mL. The compound VS5-e showed less toxicity to normal cells at the concentration required to produce an anticancer effect (with high IC50 = 973 µg/mL).Communicated by Ramaswamy H. Sarma.

Novel blue-green emitting NLOphoric triphenylamine-imidazole based donor-π-acceptor compound: Solvatochromism, DFT, TD-DFT and non-linear optical studies.

Novel Donor (D)-π-Acceptor (A) NLOphoric triphenylamine-imidazole based dye 9 was designed, synthesized, and confirmed by Mass, 13C NMR, and 1H NMR analysis. Photophysical properties of 9 were studied in solvents of different polarities and compared with analogues compounds 7 and 8. Phenonthroline acceptor based dye 9 shows highly bathochromic shifted absorption and emission compared to dyes 7 and 8. Positive solvatochromism was noticed in 7, 8, and 9 which was supported by the linear (i.e. Lippert-Mataga and Mac-Rae polarity functions) and multi-linear (i.e. Kamlet-Taft and Catalan parameters) analysis. Moreover, solvent polarizability (dSP) and solvent dipolarity (CSdP) are the major factors responsible for red shift in absorption as well as in emission spectra. Charge transfer descriptors as well as the polarity graphs are in good relation with Generalized Mulliken-Hush (GMH) parameters. NLO properties of 7, 8, and 9 were studied by using solvatochromic and computational methods. The static first hyperpolarizability (ß0) and relevant microscopic parameters (µ,α0,α,ß,γ) were determined using DFT with B3LYP, BHHLYP, and CAM-B3LYP functionals. Third-order NLO properties of nitrogen containing phenanthroline based compound 9 were observed to be several times higher than those of the compounds 7 and 8, justify the design approach.

UV protective heterocyclic disperse azo dyes: Spectral properties, dyeing, potent antibacterial activity on dyed fabric and comparative computational study.

Disperse azo dyes are synthesized and characterized by 1H NMR, 13C NMR, LC-MS, Elemental analysis, UV-visible, and fluorescence spectroscopy methods. The azo dyes show absorption maxima in the range of 460-493 nm. Dye with benzothiazole moiety i.e. VM7a and VM8a show a bathochromic shift in absorption maxima of 90 and 26 nm respectively in a polar aprotic solvent (i.e. DMF, DMSO). The dyes show deep red emission in a polar aprotic solvent (i.e. DMF, DMSO) with a Stokes shift of 62 to 180 nm. The dyes are applied on polyester fabric and the dyed fabric exhibit excellent to a good wash and sublimation fastness property. They show a very good UPF rating and almost blocking 95 to 98% of harmful UV radiation. Antibacterial activity of dyed polyester fabric is assessed qualitatively and quantitatively by using AATCC 147 and 100 test method respectively. The dyed fabrics exhibit excellent antibacterial activities against S.aureus (Gram-positive) and K. pneumoniae (Gram-negative). DFT method was used to identify the stable conformer. HOMO-LUMO gap and global reactivity descriptors were calculated using DFT method and correlated with antibacterial activities and light fastness properties respectively.

Chlorine (Cl) - Substituted Carbazole Based A-π-D-π-a Push-Pull Chromophores as Aggregation Enhanced Emission (AEE) Active Viscosity Sensors: Synthesis, DFT and NLO Approach.

Three new carbazole functionalized A-π-D-π-A extended chromophores 4a, 4b and 4c comprising of different chemical functional groups on C=C bond with the assistance of chlorovinylene group in π-conjugation are synthesized and investigated spectroscopically. We have investigated the effect of different electron acceptors - carboxycyanomethylene, dicyanomethylene and 2-(benzothiazol-2-yl) cyanomethylene, the effect of the insertion of chlorine in π-conjugation on photophysical properties and the effect of double acceptors. The chromophores 4a, 4b and 4c exhibited positive solvatochromism with large Stokes shifts and bright orange to red solid-state fluorescence. Amongst all the three compounds 4c exhibited maximum emission wavelength at 615 nm in DMSO. They presented characteristic twisted intramolecular charge transfer (TICT) emission. Observations exhibited that 4c containing long hexyl group in donor unit and 2-(benzothiazol-2-yl) cyanomethylene as an acceptor group formed an aggregate in the mixture of solvents and exhibited better aggregation enhanced emission (AEE) compared to the other two derivatives. Amongst the three styryls, 4c showed the highest emission intensity 299 a.u. at 90% water:DMF fraction (fw). Chromophores 4a-4c also exhibited good fluorescence response towards viscosity. Among the three fluorescent molecular rotors (FMR), 4c exhibited excellent viscosity sensitivity with x value = 0.687. The Non-linear (NLO) characters are estimated with the help of solvatochromic and computational methods using the functionals, B3LYP and CAM-B3LYP. The dyes showed large "linear polarizability (αCT)", "first order hyperpolarizability" (ß) and "second order hyperpolarizability" (γ) values which show that synthesized styryls can be used as a "NLO" material. The αCT, ß and γ for 4c are found to be the maximum amongst the all three dyes which can be ascribed to the smaller band gap apparent from experimental as well as DFT method.

NLOphoric benzyl substituted BODIPY and BOPHY: A comprehensive linear and nonlinear optical study by spectroscopic, DFT and Z-scan measurement.

BOPHY (BPY) and BODIPY (BDY) dye bearing benzyl group (Bn) at 4,4' and 2,6 position respectively were synthesized and characterized. The fluorescence decay measurements were performed which reveal that benzyl BOPHY (Bn-BPY) has shorter fluorescence lifetime compared to benzyl BODIPY (Bn-BDY). The difference in transition dipole moment is found to be 6.93 and 11.3 D for Bn-BDY and Bn-BPY respectively in toluene. The molecular electrostatic potential (MEP) plot shows Bn-BDY is more polarised compared to Bn-BPY. The nonlinear optical (NLO) property was evaluated using Z-scan measurement. The molecular electronic arrangement of Bn-BPY significantly affects the nonlinear absorption properties resulting into reverse saturable absorption (nonlinear absorption coefficient ß = 0.256 × 10-11 m/W). In contrast, the Bn-BDY displays saturable absorption character. The calculated third-order nonlinear susceptibility χ(3) value is 12.23 × 10-13 esu and 2.49 × 10-13 esu for Bn-BDY and Bn-BPY respectively. The power limiting behaviour of Bn-BPY displays limiting threshold energy around 70 Jcm-2 with clamped output at ~35 Jcm-2.

NLOphoric Triphenylamine Derived Donor-π-Acceptor-π-Donor Based Colorants: Synthesis, Spectroscopic, Density Functional Theory and Z-scan Studies.

Three Donor-π-Acceptor-π-Donor type styryl dyes (5a-c) with different secondary donors are synthesized and characterized to study their nonlinear and linear optical properties. The structure-property relationships of the dyes are described in the light of systematic photophysical and theoretical investigations. The photophysical characteristics of 5a-c are influenced by the polarity of the medium, with an appreciable bathochromic shift in emission (5b = 81 nm) and large Stoke shifts (5b = 104-173 nm) in polar solvents. 5a-c showed intramolecular charge transfer characteristics recognized with the help of emission solvatochromism, solvent polarity graphs, natural bond orbital analysis and HOMO-LUMO energy difference. The optimized geometry and frontier molecular orbitals reveal that the electron donation takes place from secondary donors and not from a fixed donor (triphenylamine) which is more twisted. The nonlinear optical properties obtained using solvent induced spectral shift and computational methods are found within the limiting values. Z-scan results reveal saturable kind of behavior for 5a, 5b and 5c, whereas 5a and 5b show reverse saturable kind of behavior in acetone and ethanol and hence give optical limiting values. The two-photon absorption cross section described by two-level approximation is highest for 5b (251-300 GM).

Design, synthesis, antimicrobial activity and computational studies of novel azo linked substituted benzimidazole, benzoxazole and benzothiazole derivatives.

Novel azo linked substituted benzimidazole, benzoxazole, and benzothiazole were synthesized by diazo coupling and characterized by 1H NMR, elemental analysis, FTIR and UV-vis spectroscopy. The newly synthesized compounds were evaluated for invitro antibacterial activity against Staphylococcus aureus and Escherichia Coli strains by Resazurin microtiter assay method (REMA). The minimum inhibitory concentration (MIC in µg/mL) were used to express the antibacterial activities. The azo linked compounds exhibited good to moderate or high antibacterial activities in vitro. Computational studies were performed to correlate HOMO-LUMO gap with antibacterial activity. The comparative molecular docking studies revealed better insights into binding mechanisms.

Nonlinear Optical Chromophores with Aggregation Induced Emission Enhancement Based on 2-N,N-Dibutylamino-4-Phenyl Thiazole with FMR Characteristics.

The synthesis, photophysical, linear and nonlinear optical (NLO) properties of novel fluorescent styryls based on 2-N,N-dibutylamino-4-phenyl thiazole as donor attached to different acceptor groups via conjugated π-bridge were studied with the help of solvatochromic model. The NLO properties of extended styryls based on benzylidene malononitrile and isophorone were more enhanced than the simple styryls based on malononitile and ethylcyano acetate which was attributed to the longer conjugation path. The benzylidene based extended styryl dye showed maximum value of two-photon absorption cross section σ2PA 98.85GM in dichloromethane. The 2-amino thiazole derivatives were responsive towards the viscosity of the medium hence investigated for the fluorescent molecular rotor (FMR) properties wherein almost 2.07 to 3.65 fold increase in emission intensity was observed. Also, the aggregates of these dyes in N,N-dimethyl formamide-water mixture showed enhancement in emission on aggregates formation like 3.73 fold increase in emission intensity was observed for benzylidene based extended styryl dye. Thus NLOphoric AIEgens with FMR properties emitting in the red region of the electromagnetic radiation were developed.

Design and Synthesis of Coumarin-Imidazole Hybrid Chromophores: Solvatochromism, Acidochromism and Nonlinear Optical Properties.

A set of linear and asymmetric coumarin-imidazole hybrid compounds having a N,N-diethylamine at 7-position and imidazole at 3-position on the coumarin were synthesized. Insertion of thiophene π-spacer between coumarin and imidazole moieties (5b, 5d) leads to redshifted absorption and emission compared to 5a and 5c. All the compounds show a noticeable response to trifluoroacetic acid with a redshifted absorption and an increase in emission intensity by twofold. The ratio of ground and excited state acidity constant was calculated using Förster energy cycle, and the ratios were found to be 0.25, 0.96, 0.52 and 1.87, respectively, for 5a-5d. Due to the thiophene π-spacer, elongation of π-conjugation in 5b and 5d leads to high values of polarizability (α), first-order hyperpolarizability (ß) and second-order hyperpolarizability (γ). Compound 5b exhibits a high value (895 GM) of two-photon absorption cross section (σ2PA), measured using two-level model.

Molecular and NLO Properties of Red Fluorescent Coumarins - DFT Computations Using Long-Range Separated and Conventional Functionals.

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 (α0), hyperpolarizability of the first order (ß0) 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 α0, ß0, 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.

Non-linear optical response of meso hybrid BODIPY: Synthesis, photophysical, DFT and Z scan study.

Hybrid meso BODIPY dyes are synthesized and their linear and non-linear optical properties are studied. Time-resolved fluorescence lifetime decay is found to be identical for all dyes irrespective of meso substituents. The Z-scan experiment performed to calculate the nonlinear absorption coefficient (ß) and third-order nonlinear susceptibility (χ3). Global hybrid (B3LYP and BHHLYP) and range-separated hybrid (CAM-B3LYP) functional with the basis set 6-311++G(d,p) was employed to determine the theoretical linear and non-linear optical properties. The computed ß0 value of all the three dyes was found to be superior to that of urea (ßo = 0.371 × 10-30 esu). Introduction of meso substituent directly affects the polarizability and second-order hyperpolarizability of the dyes. Thermal and reorientational effect of the investigated NLOphoric dyes were studied.

Fluorescent 7-Substituted Coumarin Dyes: Solvatochromism and NLO Studies.

The effect of three substituents N,N-diethylamine, carbazole and diphenylamine at the 7 position of coumarin on linear and nonlinear optical properties are studied using absorption and emission solvatochromism, and DFT. By varying the substituent 53 nm red shift is achieved in emission. The polarity plots with regression close to unity revealed good charge transfer in the system. Solvent polarizability and dipolarity are mainly responsible for solvatochromic shift as proved by multilinear regression analysis. General Mulliken Hush analysis shows diphenylamine substituent leads to more charge separation in compound 6c. The hyperpolarizabilities are evaluated by quantum mechanical calculations. Structure of the compounds are optimized at B3LYP/6-31G(d) level and NLO computations are done using range separated hybrid functionals with large basis sets. Second order hyperpolarizability (γ) found 589.27 × 10-36, 841.29 × 10-36 and 1043.00 × 10-36 e.s.u for the compounds 6a, 6b and 6c respectively.