•Novel strategy is used for the synthesis of triphenylamine-isophorone styryl dyes.•Tri-formylation of triphenylamine easily occurred due to the methoxy support.•The dyes are categorized into ICT and TICT dyes as per their viscosity sensitivity.•Red shifted absorptions-emissions are observed due to the auxiliary methoxy donors.A novel strategy for the synthesis of triphenylamine based and methoxy supported deep red emitting push-pull chromophores is developed. The methoxy groups though not in conjugation with the acceptor exhibited a red shifted absorption and emissions (670 nm) as compared to the unsubstituted analogues due to the improved donating ability of triphenylamine. The dyes show high molar extinction coefficients (1, 65,800 M−1 cm−1) and as the number of withdrawing groups increases the molar extinction coefficient and emission intensity increase. Positive solvatochromism (96 nm) was observed which is well supported by linear and multi-linear regression. The mono styryl dyes showed enhancement of fluorescence while the di and tri-styryl dyes show quenching of fluorescence in polar solvents, which is correlated with the intramolecular charge transfer and twisted intramolecular charge transfer. Viscosity induced emission enhancement has also been observed. The experimental findings were correlated theoretically by using Density Functional theory computations.

•Synthesis of triphenylamine based novel coumarin-rhodamine hybrid dyes.•In their open form they show absorption and emission peaks in the deep red region.•Larger Stokes shift than reported rhodamine dyes RH-B and RH-101 are found.•They exhibit viscosity sensitivity in visible as well as deep red region.•Solvent polarity and viscosity works together for the observed emission enhancement.We designed and synthesized triphenylamine based and coumarin fused rhodamine hybrid dyes and characterized using 1H, 13C NMR and HR-LCMS analysis. Both the newly synthesized hybrid dyes were found to show red shifted absorption as well as emissions and large Stokes shift (40–68 nm) as compared to the small Stokes shift (25–30 nm) of reported dyes Rhodamine B and 101. Photophysical properties of these dyes were studied in different solvents and according to the solvents acidity or basicity they preferred to remain in their spirocyclic or open form in different ratio. We studied the spirocyclic as well as open form derivatives of these dyes for their viscosity sensitivity in three different mixture of solvents i.e. polar-protic [EtOH-PEG 400], polar-aprotic [toluene-PEG 400] and non-polar-aprotic [toluene-paraffin]. They are found to show very high viscosity sensitivity in polar-protic mixture of solvents [EtOH-PEG 400] and hence concluded that both polarity as well as viscosity factor worked together for the higher emission enhancement rather than only viscosity factor. As these dyes showed very high viscosity sensitivity in their spirocyclic as well as open form, they can be utilized as viscosity sensors in visible as well as deep red region. We also correlated our experimental finding theoretically by using Density Functional theory computations.

•Two novel red emitting BODIPY dyes with a large Stokes shift are reported.•The dyes are sensitive towards acid and polarity of microenvironments.•Fluorophores shows TICT on-off characteristics.•These fluorophores can be used as potential pH probes.•The dyes possess high values of βCT thus can be used as promising NLO materials.Two new red emitting difluoro-boradiazaindacene fluorophores have been synthesized, and their photophysical and hyperpolarizability properties in various microenvironments were evaluated experimentally and characterized in detail with respect to DFT and TD-DFT using B3LYP/6-31G(d) level of theory. The dyes possess reasonable first order hyperpolarizabilities in solvents of different polarities. The photophysical properties of the difluoro-boradiazaindacene cores are found to be highly sensitive towards change in polarity of microenvironments because of twisted intramolecular charge transfer (TICT) characteristics. The dyes show unusually very large Stokes shifts and their photophysical properties such as emission maxima and fluorescence intensity were altered to a great extent in the presence of trace amount of TFA in chloroform. These dyes can be used as promising candidates for pH probes and non-linear optical materials.

•Excellent negative absorption solvatochromism.•Solvatochromism is analyzed successfully using polarity scales.•Excited state dipole moment decreases as solvent polarity increases.•Dyes shows positive and negative nonlinear optical properties.Five mono-azo dyes were synthesized using different diazotized aromatic amines followed by coupling with 1, 3-dihydroxy-2-naphthoate and characterized by proton and carbon NMR and elemental analysis. DFT optimized geometries of all the dyes suggest that dyes are present in the hydrazone form in the ground state and not in the azo form. They showed strong negative absorption solvatochromism and were studied using various solvent polarity scales and multilinear regression analysis using Kamlet – Taft and Catlan scales. Dyes are weakly fluorescent in solvents. Dyes were compared with a parallel series of dyes using 2-naphthol and azo dyes based on benzothiazole unit to investigate the effect of hydroxyl naphthalene ester moiety on the photophysical properties. Solvatochromism was used to calculate the excited state dipole moment, linear and nonlinear optical properties of these dyes. The excited state dipole moments found higher than the ground state dipole moments in case of dye 3a, 3b and 3c while lower than the dyes 3d and 3e respectively. The dyes were also found to be sensitive to pH. Positive and negative values are found for second hyperpolarizability. All these features indicates that present dyes have potential for the advanced applications such as third order nonlinear optical materials.

•Structure property relationship study of Pyrazino-phenanthroline rigid compounds.•Positive and negative acidochromism is observed after the addition of TFA.•Solvatochromism is explained using Kamlet-Taft and Catalan multilinear analysis.•Calculation of difference in dipole moment and optical band gap.•Theoretical study using TD-DFT computation is performed.Donor-π-acceptor-π-auxiliary acceptor type compounds have been designed and synthesized to study their rigidity and structural effects on optical properties. Structural variation is achieved by changing the central π-conjugated core with naphthalene, acenaphthene and phenanthrene based donor-π-acceptor compounds containing N, N-diethyl aniline or morpholine as donor and pyrazine ring fused with phenanthroline as acceptor. A detailed study of positive and negative acidochromism is performed. Intramolecular charge transfer, solvatochromism and highly polar excited state of these compounds are elucidated by Lippert-Mataga, Mac-Rae and Reichardt correlations. Multilinear regression analysis using Kamlet-Taft and Catalan parameters is also performed to support the observed solvatochromism in absorption and emission spectra from non-polar to polar solvents. All the spectroscopic results were correlated theoretically by Density Functional Theory (DFT) computations.

•Thiazole based styryl (push-pull) fluorophores are made and spectroscopic properties are investigated.•NLO properties are evaluated using spectroscopic and DFT methods.•BLA index and generalized Mulliken-Hush (GMH) analysis are performed to understand the charge transfer.•The chromophores possesses very high thermal decomposition temperatures (Td).Novel push-pull fluorophores constituted by two donors (substituted pyrrole and morpholine) linked to acceptor through thiazole electron spacer have been synthesized. The fluorophores are investigated for linear and non-linear optical properties by UV-VIS absorption and fluorescence spectroscopies, and by means of TD-DFT (B3LYP/6-31G(d)) method, with the aim of elucidating the ability of the morpholine/pyrrole-donor-thiazole-spacer based D-π-A fluorophores as organic NLO materials. The bond length alternation and generalized Mulliken-Hush (GMH) analysis is performed to understand the involvement of the donor in effective transfer of the charge to acceptor. Values of first-order hyperpolarizabilities (βCT or β0), obtained by the solvatochromic method (Lippert Mataga model), and the transition dipole moments (μeg) used to characterize and evaluate the non-linear optical performances of the D-π-A fluorophores in various microenvironments. The D-π-A fluorophores possess good values of βCT or β0 in different organic solvents and hold high thermal stabilities therefore can be used as potential organic NLO materials.

•DFT and Solvatochromic studies of triphenylamine based dyes.•Calculations of first and second order hyperpolarizabilities.•NLO property evaluation of triphenylamine based dyes.•Enhancement in NLO properties by introduction of Benzothiazole unit.The static first and second hyperpolarizability and their related properties were calculated for triphenylamine-based “push-pull” dyes using the B3LYP, CAM-B3LYP and BHHLYP functionals in conjunction with the 6-311+G(d,p) basis set. The electronic coupling for the electron transfer reaction of the dyes were calculated with the generalized Mulliken-Hush method. The results obtained were correlated with the polarizability parameter αCT, first hyperpolarizability parameter βCT, and the solvatochromic descriptor of 〈γ〉 SD obtained by the solvatochromic method. The dyes studied show a high total first order hyperpolarizability (70–238 times) and second order hyperpolarizability (412–778 times) compared to urea. Among the three functionals, the CAM-B3LYP and BHHLYP functionals show hyperpolarizability values closer to experimental values. Experimental absorption and emission wavelengths measured for all the synthesized dyes are in good agreement with those predicted using the time-dependent density functional theory. The theoretical examination on non-linear optical properties was performed on the key parameters of polarizability and hyperpolarizability. A remarkable increase in non-linear optical response is observed on insertion of benzothiazole unit compared to benzimidazole unit.Download high-res image (160KB)Download full-size image

•Benzophenone-based chemosensor for Sn2 + has been synthesized.•Specific selectivity and superiority of our fluorophore over the only reported fluorophore for Sn2 + ion sensing (along interference of Al3 +ion) is explained.•Sn2 + recognition was investigated by spectroscopic techniques and DFT study.Synthesis of novel benzophenone-based chemosensor is presented for the selective sensing of Sn2 + ion. Screening of competitive metal ions was performed by competitive experiments. The specific cation recognition ability of chemosensor towards Sn2 + was investigated by experimental (UV–visible, fluorescence spectroscopy, 1H NMR, 13C NMR, FTIR and HRMS) methods and further supported by Density Functional Theory study. The stoichiometric binding ratio and binding constant (Ka) for complex is found to be 1:1 and 1.50 × 104, respectively. The detection limit of Sn2 + towards chemosensor was found to be 0.3898 ppb. Specific selectivity and superiority of chemosensor over another recently reported chemosensor is presented.

•Triphenylamine donor with auxiliary methoxy and dicyanovinyl acceptor interacting via isophorone as a configurationally locked polyene π-bridge are investigated as efficient NLOphores.•Push-pull chromophores exhibit significant ICT character on the virtue of GMH analysis and Lippert-Mataga plots.•Linear and non linear optical properties are evaluated by spectroscopic, theoretical (TDDFT) methods and Z-scan analysis.•All chromophores exhibit very high thermal stabilities with the decomposition temperatures higher than 340 °C.Molecules containing methoxy supported triphenylamine as strong electron-donor and dicyanovinyl as electron-acceptor groups interacting via isophorone as a configurationally locked polyene π-conjugated bridge are studied for their nonlinear optical properties. The photophysical study of examined chromophores in non-polar and polar solvents suggest that they exhibit strong emission solvatochromism and significant charge transfer characteristics supported by Lippert-Mataga plots and Generalised Mulliken Hush analysis. Linear and nonlinear optical properties as well as electronic properties measured by spectroscopic methods and cyclic voltametry and supported by DFT calculation were used to elucidate the structure property relationships. All three chromophores exhibit very high thermal stabilities with the decomposition temperatures higher than 340°C. The vibrational motions play very important role in determining the overall NLO response styryl chromophores which was established by DFT study. Dye 3 with maximum nonlinear optical susceptibility among three D-π-A systems proves that the multibranched push-pull chromophores exhibit a higher third order nonlinear susceptibility and justifies the design strategy.Download high-res image (278KB)Download full-size image

•First report on theoretical study on NLO properties of benzo[h] coumarins.•Compounds shows good solvatochromism and NLO properties.•CAM-B3LYP is found to be better functional to calculate vertical excitation properties and NLO properties.•Computed NLO properties are close to maximum limit of hyperpolarizability.Three benzo[h] coumarins were synthesized and analyzed for their potential NLOphoric properties. Coumarins were synthesized using Knoevenagel condensation method by reacting hydroxyl-naphthalene aldehyde with cyano-methylelene-benzazoles containing NH, O and S elements respectively as the active methylene compounds. The absorption maxima for the coumarins are not affected by the solvent polarity but emission maxima does. Emission solvatochromism was analyzed using various solvent polarity functions which highlights the polarity dependency of the emission profile. Coumarins showed satisfactory values for first and second hyperpolarizability which are comparable using solvatochromism and DFT. NLO properties are also compared with the limits of hyperpolarizability calculated using sum rule of quantum mechanics. Results show that the NLO properties predicted by DFT are close to the upper limits of hyperpolarizability. The functional CAM-B3LYP is proven to be suitable for predicting NLO properties for these coumarins compared to functional B3LYP. The present study highlights the importance of such molecules for incorporating in advanced NLOphores.Download high-res image (251KB)Download full-size image

Density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations of two excited state intramolecular proton transfer (ESIPT) molecules [2,5-bis(2-benzothiazolyl)hydroquinone and 2,5-bis(benzo[d]thiazol-2-yl)-4-methoxyphenol] were performed to study their structural and photo-physical behavior upon excitation. The most stable structure was established by optimizing all possible rotamers. The vertical excitation and emission wavelengths obtained by using TD-DFT show very good correlation with the experimental values. A correlation has been established based on the absorption values to determine the contribution of stable rotamers.

Using density functional theory approach, the trend in photostability of fluorescent coumarin laser dyes were investigated with the help global reactivity descriptors. The effect of different basis sets on global reactivity descriptors i.e. electrophilicity index (ω) is studied. The local reactivity descriptors such as Fukui function, local softness and local electrophilicity index have been used to understand the reactive site in the molecule. Photodegradation mechanism of fluorescent coumarin laser dyes in presence of singlet oxygen is explained using density functional theory.

•Synthesis of novel red emitting carbazole-coumarins.•DFT studies on the carbazole-coumarin dyes.•Photophysical and spectroscopic studies of novel coumarin dyes.•NLO properties of carbazole-coumarin dyes.The carbazole core is known to be a very efficient donor and can assist the coumarin core in achieving the red emission by pushing electrons in the chromophoric system. 9-ethyl-9H-carbazole-3-carbaldehyde and 9-ethyl-9H-carbazole-3,6-dicarbaldehyde were reacted with 3-acetyl-4-hydroxy-coumarin and 7-(N,N-diethylamino)-3-acetyl-4-hydroxy-coumarin to give the corresponding hybrids. The BF2-complexes of the 4-hydroxy-3-acetyl-coumarin derivatives were reacted to give the coumarin-carbazole hybrids. The molecules synthesized emit in the red region. Their photophysical properties were studied in various solvents of different polarity. The solvent polarity function plots were studied and show linearity. The introduction of two units of coumarin core on carbazole improves the molar extinction co-efficient of the dye. The BF2-complexation has enhanced the quantum efficiency and non-linear optical properties of the molecules.

•Novel carbazole based push–pull dyes were synthesized.•Dyes exhibited aggregation-enhanced emission and solvatochromism.•Dipole moment determination using solvatochromism and DFT method.•Nonlinear optical property study based on solvatochromism and DFT.•DFT and TDDFT computation were performed for photophysical property study.2-Alkoxy-9-methyl-9H-carbazole-3-carbaldehyde based push pull chromophore were efficiently synthesized by a multi-step reaction starting from 9H-carbazole-2-ol. The fluorescence properties of these D–π–A chromophores were investigated in various solvents of varying polarities and in mixed solvent solutions of DMF and H2O. They exhibited low fluorescent intensity in solution but a high fluorescent intensity in aggregate forms and in their solid state due to the promising aggregation-induced emission enhancement characteristics. These dyes were fully characterized by FT-IR, 1H NMR and HRMS spectra. The ratio of ground to excited state dipole moment of the novel push pull chromophore were calculated by Bakhshiev and Bilot–Kawski correlations. All the four dyes show more or less twisted intramolecular charge transfer (TICT) characteristics. They show a large first hyperpolarizability value ranging from 189–721 × 10−30 esu by theoretical method and 73–330 × 10−30 esu by experimental method.

•Novel pyrazole based push–pull dyes were synthesized and characterized.•Photophysical properties estimated using experimental method are in good agreement with the theoretical results.•DFT computation was performed for determination of nonlinear optical (NLO) properties.•Pyrazole based dyes exhibited large second order hyperpolarizabilities.A series of pyrazole based D-π-A derivatives have been synthesized from 3-(4-nitrophenyl)-1-pheny-1H-pyrazole-3-carbaldehyde with series of active methylene compounds. The dyes were well characterized by FT-IR, 1H NMR, 13C NMR, elemental analysis and mass spectroscopy. The synthesized dyes absorb in the range of 351–432 nm. Experimental absorption wavelengths for compounds are in good agreement with those predicted using the Time-Dependent Density Functional Theory (TD-DFT) [B3LYP/6-31G(d)]. Density Functional Theory calculations were performed to determine the static first hyperpolarizability (β0) and related properties (μ, α, Δα, β0 and γ) for pyrazole based “donor-π-acceptor” dyes 3a–3f, using B3LYP functional with 6-31G (d) basis sets at the ground state. The computed values for these dyes show high first order hyperpolarizability in the range 50.64–256.38 × 10−30 esu and second hyperpolarizability (γ) in the range of 235.71–1580.81 × 10−36 esu.

•Novel push–pull type of styryl derivatives from thiazole carbaldehyde.•Photophysical properties of styryl derivatives supported by TD-DFT computational data.•Dye 6b shows good fluorescence intensity in solid state, dye 6c shows red shifted absorption and emission.•Non-linear optical properties using solvatochromic method and density functional theory in different polarities of solvent.Multi-step synthesis was achieved to obtain new generation push–pull dyes containing benzimidazole fluorophore and thiazole unit. A largest Stokes shift of 114 nm in acetonitrile is observed in extended styryl among all the dyes. Density functional theory and time dependent-density functional theory computations have been used for comparative study with the experimental data and also to understand the substitution or steric effect on structural, molecular, electronic and photophysical parameters of the benzimidazole fluorophore of the thiazole based styryl dyes. First-order hyperpolarizability, using solvatochromism and solvent dependent shifts in emission wavelengths and the transition dipole moments were used to characterize and evaluate the second-order nonlinear optical performances of the styryl dyes in different organic solvents. The density functional theory method was also employed to investigate the non-linear optical properties of the styryl dyes in different solvent media. The substituted benzimidazolyl thiazolestyryl dyes possess good non-linear optical properties.

•Synthesis of carbazole based extended styryls having better photophysical properties.•Synthesized extended styryl act as florescent molecular rotors.•The photophysical properties of the extended styryl were investigated in different solvent polarity.Carbazole based D-π-A extended styryl dyes with intramolecular charge transfer characteristics were synthesized. The intramolecular charge transfers of these D-π-A extended styryls have been examined with the study of photophysical properties like absorption, emission and quantum yield in various solvents of different polarities. All the dyes demonstrated positive solvatochromism. They showed largely improved photophysical properties and large Stokes shifts due to twist geometry. Oscillator strengths and transition state dipole moments have been studied to understand charge transfer within the molecules. The fluorescence molecular rotors properties of the series of extended styryls have been evaluated. The dyes having good charge transfer characteristics showed better FMR properties. Sensitivity of the fluorescence emission towards solvent polarity and viscosity has been investigated using fluorescence emission spectra.

In this paper, we report two new 2H-pyran-3-carbonitrile derivatives having two different coumarin parental units with intramolecular charge transfer (ICT) and twisted intramolecular charge (TICT) properties. The absorption and emission spectra are studied in different organic solvents at room temperature. The dye 3b shows red shifted absorption and emission compared to the dye 3a because of the rigidized structure. 2H-pyran-3-carbonitrile derivatives exhibit strong fluorescence properties in various solvents and show positive solvatochromism. The dyes 3a and 3b show maximum fluorescence quantum yield in chloroform and tetrahydrofuran (ϕ: 0.81, 0.90). The bathochromic shift of absorption/emission spectra and increase in dipole moment after excitation of the dyes 3a and 3b indicate the intramolecular charge transfer (ICT)/Twisted intramolecular charge transfer (TICT) character of the emitting singlet state. Density functional theory (DFT) and time dependent-density functional theory (TD-DFT) computations have been used to understand the structural, molecular, electronic and photophysical parameters of the push-pull dyes. The ratio of ground to the excited state dipole moment of the synthesized dye is calculated with the help of Bakhshiev and Bilot–Kawski correlations.

Two boron-dipyrromethene dyes with N-phenylcarbazole core at meso position were prepared and characterized. They show small Stokes shifts (15–20 nm), high molar extinction coefficient and high quantum yield. Their photophysical properties were compared with the known meso aryl, 4-aminophenyl, N,N-dimethylaniline and N-butylcarbzole boron-dipyrromethene dyes. The bulky nature of N-phenylcarbazole leads to an increase in molar absorptivity and quantum yield. The Catalan solvent parameters are found to be the suitable for defining the solvatochromic absorption and emission properties. Confocal laser scanning microscopy showed solid-state fluorescence. Density Functional Theory is used to determine the static first hyperpolarizability (βο) and its components (μ, α0, Δα, and γ) using B3LYP/6-31G(d) at ground state and excited state in different polarity solvent. The geometries of the dyes were optimized by using B3LYP/6-31G(d) and their electronic excitation properties were estimated using time dependent density functional theory.

•Two novel coumarin-thiazole hybrid derivatives were synthesized.•Resonance induced excited state intramolecular proton transfer phenomenon (RI-ESIPT).•Bond order alternation and density functional theory supports the RI-ESIPT.•Near Infrared emitting dye.Two novel coumarin thiazole hybrid dyes (E)-2-(3-(2-(4-(4-hydroxy-2-oxo-2H-chromen-3-yl)-2-morpholinothiazol-5-yl)vinyl)-5,5-dimethylcyclohex-2-en-1-ylidene)malononitrile (CSI) and (E)-2-(3-(2-(4-(4-methoxy-2-oxo-2H-chromen-3-yl)-2-morpholinothiazol-5-yl)vinyl)-5,5-dimethylcyclohex-2-en-1-ylidene)malononitrile (MeOCSI) were synthesized. CSI exhibits near infrared emission with very large Stokes shift. The dye CSI shows resonance induced excited state intramolecular proton transfer (RI-ESIPT). DFT and TD-DFT calculations clearly support and define the finding.

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.

•Carbazole based donor–acceptor dyes: synthesis, photophysical properties evaluation.•Solvatochromism data were used for experimental dipole moment determination and well supported by DFT computations.•Solvatochromism data were used for experimental determination of nonlinear optical (NLO) properties.•DFT computation were performed for determination of nonlinear optical (NLO) properties.Photophysical properties of novel carbazole containing “push–pull” dyes obtained by the condensation of 2-methoxy-9-methyl-9H-carbazole-3-carbaldehyde 3 with different active methylene moieties are studied. These dyes were well characterized by 1H NMR, 13C NMR and HRMS spectra. The UV–vis absorption and fluorescence emission spectra of the dyes were studied in solvents of varying polarities. DFT and TD-DFT computation were performed to study structural, molecular, electronic and photophysical parameters of the dyes. The four dyes are showing red shifted solid sate emission in the range of 487–593 nm. The ratio of ground to excited state dipole moment of the synthesized dyes were calculated using solvent polarity correlations and DFT method. The absorption wavelength and emission wavelength values are found to be in good agreement with the experimental results. Non-linear optical properties were investigated by using solvatochromic shift method and theoretical methods.Download high-res image (122KB)Download full-size image

Two novel BODIPY (pyrromethene, PM) dyes containing N-ethyl carbazole at the meso position are synthesized and their photophysical properties in different solvents and the photochemical stabilities and laser performances in n-heptane are investigated. The n-heptane solution of the dyes was used as a gain medium in a constructed narrow band dye laser, pumped by a Q-switched (10 Hz) frequency-doubled (532 nm) Nd:YAG laser and the results gave enhanced photo stabilities and similar peak efficiencies of the synthesized dyes as compared to parent dye PM567. When substituted at the meso position with N-alkyl carbazole, photostability is found to be increased in comparison to PM567, and also when substituted at 2- and 6-positions with a benzyl group instead of an ethyl group along with N-ethyl carbazole at the meso position, the photo stability is further increased in n-heptane. A comprehensive study on structural, photophysical and electronic properties of dyes by means of DFT and TD-DFT in the solvents of various polarities has revealed remarkable characteristics of the BODIPY chromophore.

Two novel acridine based chemosensors 7a and 7b were synthesized and configured as “fluorophore–spacer–receptor” systems based on photoinduced electron transfer. The probes 7a and 7b exhibited high selectivity and sensitivity for the detection of Cu2+ and Al3+ respectively over commonly coexistent metal ions in CH3CN. The binding association constants (Ka) of 7a–Cu2+ and 7b–Al3+ were found to be 4.0 × 104 M−1 and 1.7 × 104 M−1 in CH3CN, and the corresponding detection limits were calculated to be 2.8 × 10−7 M and 5.8 × 10−7 M, respectively. The fluorescence response of 7a–Cu2+ and 7b–Al3+ with respect to pH change was studied and the resulting demonstrated fluorescence enhancement was observed in the pH range of 7.0–9.0. The chromophores were characterized by FT-IR, 1H-NMR, 13C-NMR and HR Mass spectral analysis.

•First unique study of blue-emitting ESIPT triazoles.•Improved photophysical properties compared to similar analogues.•Experimental and TDDFT data on photophysical properties.•Dipole moments from solvatochromic data.Three novel 2-{2-[4-(N,N-diethylamino)–2–hydroxyphenyl]–1H–benzo[d]imidazol–6–yl}–2H–naphtho [1,2-d] [1,2,3] fluorescent triazole derivatives were synthesized from 2-(5-amino-1H-benzimidazol-2-yl)-5-(N,N-diethylamino)phenol and amino substituted naphthylsulphonic acids. The absorption, emission, quantum yields and dipole moments of these compounds were evaluated in methanol, acetonitrile, N,N-dimethylformamide and dimethylsulfoxide. The compounds 8a and 8c absorb in the near visible region, while compound 8b shows two absorption peaks, short wavelength peak is in the near visible region and long wavelength absorption in the visible region. Compounds are fluorescent in solution and emit in blue and green region. The photophysical properties of the 8a–8c were compared with structural analogs reported till date. The experimental absorption and emission properties were compared with the theoretical data obtained by DFT and TD-DFT computations with TD–B3LYP and CAM–B3LYP functional with 6–31G (d) and 6–311G (d) basis sets. Theoretical results obtained by TD-B3LYP functional are well in line with the experimental results. The compounds are thermally stable up to 300 °C. New compounds were characterized by spectral techniques.

The non-fluorescent meso diaminophenyl 1,3,5,7-tetramethyl BODIPY dye has been investigated and employed for picric acid sensing in a constructive way by regenerating its fluorescence through PET hindrance. A strong enhanced emission signal was obtained as a consequence of the electrostatic association between the BODIPY probe and picric acid with specific recognition among other explosive nitroaromatics. The probe shows a 1:1 binding stoichiometry with picric acid and a detection limit of up to 0.65 ppb.

In an attempt to develop photostable and efficient BODIPY (PM) dyes for use in liquid dye lasers, three new congeners of widely used laser dye, PM567, were synthesized and their photophysical properties in various organic solvents, laser performances, and photostabilities in a selected solvent, 1,4-dioxane, have been investigated using a frequency doubled Q-switched (10 Hz) Nd:YAG laser at 532 nm. The results of photostability study in nonpolar 1,4-dioxane revealed the remarkable enhancement in stability of the novel dyes compared to that of PM567 as well as improved laser performances. Cyclic voltammetry study strongly supports the observed enhancement in photostability of the novel dyes compared to that of PM567. The observed properties of the novel dyes in relation to those of PM567 have been rationalized by extensive use of DFT and TD-DFT using the B3LYP/6-31G(d) method of theory.

•Synthesis and characterization of 3-(1,3-benzothiazol-2-yl)-2-hydroxynaphthalene-1-carbaldehyde 4.•Incorporation of benzothiazole ring at the 3-position in naphthalene ring leads to solid state fluorescence.•Existence of ESIPT has been theoretically predicted by computational method.•Photophysical properties have been studied experimentally and correlated with computational results.Excited state intramolecular proton transfer inspired 3-(1,3-benzothiazol-2-yl)-2-hydroxynaphthalene-1-carbaldehyde, showing solid state fluorescence has been synthesized. Existence of excited state intramolecular proton transfer process between carbonyl group and phenolic OH group has been theoretically predicted using computational method. Density functional theory and time dependent density functional theory computations have been used to investigate structural parameters and understand the photophysical properties of the synthesized carbaldehyde. The photophysical properties of carbaldehyde were evaluated using UV–Visible and fluorescence spectroscopy and are found to be very sensitive to the microenvironment such as solvent polarity and pH. The experimental absorption–emission a results are correlated with the computed values. The increase in the dipole moment of A2-Keto* than A2-Enol* suggested the presence of keto form in the excited state and which is responsible for the single fluorescence emission with a large Stokes shift in all solvents.Graphical abstractIntroduction of benzothiazole ring at the 3-position in the ESIPT molecule, 2-hydroxy-1-naphthaldehyde leads to solid state fluorescence. Existence of ESIPT process in oxygen of carbonyl group and phenolic OH group has been theoretically confirmed by computational method.

•Synthesis of Schiff’s bases from 3-(1,3-Benzothiazol-2-yl)-2-hydroxynaphthalene-1-carbaldehyde.•Photophysical properties of all Schiff’s bases have been studied experimentally in different solvents.•Photophysical properties of Schiff’s base 6a have been investigated theoretically and correlated to the experimental results.•DFT and TD-DFT computation have been used to investigate the structural parameters and geometry of 6a.A series of novel Schiff’s bases have been synthesized from 3-(1,3-benzothiazol-2-yl)-2-hydroxynaphthalene-1-carbaldehyde. The presence of hydroxyl group ortho to the benzothiazolyl group as well as the imine linkage lead to the occurrence of excited state intramolecular proton transfer process. The computational strategy was used to study the ESIPT process of the synthesized Schiff’s bases, which revealed surprisingly that the keto form predominantly exists in the ground state contradicting the ESIPT process. Density functional theory and time dependent density functional theory have been used to investigate the structural parameters and photophysical properties in different solvents of one of the Schiff’s bases. The experimental results correlate well with the computed results. All Schiff’s bases show good thermal stability.Presence of hydroxyl group at ortho position to benzothiazole ring as well as imine linkage may lead to the existence of ESIPT process. But computational study of one of the Schiff’s bases reveals that keto form is more stable than enol form at ground state in gas as well as in solvent phase. Thus ESIPT process does not exist in synthesized Schiff’s bases.

•Synthesized novel ESIPT Inspired compounds which are unknown to this date, synthesis route is very easy and reproducible.•Existing fluorescein compounds shows single absorption in UV region having restricted applications are overcome by introducing ESIPT unit in fluorescein core.•First and unique study of fluorescein compounds having pH sensitive dual absorption-emission characteristics.•Relative fluorescence quantum yield of fluorescein derivatives were investigated.•Experimental photophysical properties were compared with TD-DFT computational data.A series of novel substituted ESIPT benzothiazole fluorescein derivatives were synthesized from the intermediate, (1H-benzo[d]thiazole-2-yl) benzene-1,3-diol and different anhydrides. The photophysical properties of these fluorescein derivatives were studied as a function of pH and viscosity. Enhancement in fluorescence emission was observed with increasing percentage of glycerin in water. The relative fluorescence quantum yields of these derivatives were determined by using anthracene and fluorescein as a reference standards. Density Functional Theory computations were performed to optimize the geometry at the ground state. The excited state geometry was optimized using the time dependent-DFT. The synthesized fluorescein derivatives were characterized by using elemental analysis, FT-IR and 1H NMR spectroscopy.ESIPT inspired benzothiazole based fluorescein derivatives were synthesized by reacting the intermediate, (1H-benzo[d]thiazole-2-yl) benzene-1,3-diol with different substituted anhydrides. Effects of pH and viscosity on photophysical characteristics of ESIPT fluorescein derivatives were studied. Experimental photophysical properties were compared with density functional theory calculations.

A greener approach for the synthesis of quinazoline intermediates using an ionic liquid was developed where the ionic liquid is used as an intrinsic reaction catalyst and a solvent. Merits of this reaction are self-catalysis, easy workup process, less reaction time, and environmental friendliness.

In an endeavor to find a new class of antimicrobial agents, a series of 2-(1H-benzimidazol-2-yl)-5-(diethylamino)phenol, 2-(1,3-benzoxazol-2-yl)-5-(diethylamino)phenol, 2-(1,3-benzothiazol-2-yl)-5-(diethylamino)phenol and their derivatives were synthesized starting from p-N,N-diethyl amino salicylaldehyde with different substituted o-phenylenediamine or o-aminophenol or o-aminothiophenol. The newly synthesized compounds were characterized by FT-IR, 1H NMR and LC–MS analysis. All compounds were evaluated for in vitro antibacterial activities against Escherichia coli and Staphylococcus aureus strains and in vitro antifungal activity against Candida albicans and Aspergillus niger strains by using serial dilution method. The antibacterial activities were expressed as the minimum inhibitory concentration (MIC) in μg/mL.Novel benzimidazole, benzoxazole and benzothiazole derivatives were designed and synthesized from p-N,N-diethyl amino salicylaldehyde with different substituted o-phenylenediamine or o-aminophenol or o-aminothiophenol. Antimicrobial activities were tested against bacterial strain (Escherichia coli, Staphylococcus aureus) and fungal strain (Candida albicans and Aspergillus niger), results reveals that compounds have potent antimicrobial activity.Figure optionsDownload full-size imageDownload high-quality image (84 K)Download as PowerPoint slide

•2-Imidazole substituted BODIPY dye has been selected for the nonlinear optical studies.•Solvatochromic method and Z scan technique have been employed for determining the NLO properties.•DFT calculations have been performed to estimate the NLO response of the dye.BODIPY chromophore flanked with the benzimidazole moiety at 2-position has been investigated for its nonlinear optical (NLO) properties. Charge transfer character developed by the unsymmetrical substitution on the molecular framework and the solvatochromic behaviour of this dye inspired us to study its NLO characteristics. NLO response has been measured using solvatochromic method as well as the Z scan technique. The values obtained for nonlinear absorption coefficient (β) and third order susceptibility χ(3) are −7.45 × 10−12 and 3.85 × 10−13 respectively. Quantum chemical calculations have also been performed to estimate the NLO properties theoretically by using DFT method with three functionals viz B3LYP, BHHLYP and CAMB3LYP with 6-311 G (d,p) basis set. The results obtained from the DFT method are in well accordance with those produced from solvatochromic method.

Two novel BODIPY (pyrromethene, PM) dyes containing N-ethyl carbazole at the meso position are synthesized and their photophysical properties in different solvents and the photochemical stabilities and laser performances in n-heptane are investigated. The n-heptane solution of the dyes was used as a gain medium in a constructed narrow band dye laser, pumped by a Q-switched (10 Hz) frequency-doubled (532 nm) Nd:YAG laser and the results gave enhanced photo stabilities and similar peak efficiencies of the synthesized dyes as compared to parent dye PM567. When substituted at the meso position with N-alkyl carbazole, photostability is found to be increased in comparison to PM567, and also when substituted at 2- and 6-positions with a benzyl group instead of an ethyl group along with N-ethyl carbazole at the meso position, the photo stability is further increased in n-heptane. A comprehensive study on structural, photophysical and electronic properties of dyes by means of DFT and TD-DFT in the solvents of various polarities has revealed remarkable characteristics of the BODIPY chromophore.

A greener approach for the synthesis of quinazoline intermediates using an ionic liquid was developed where the ionic liquid is used as an intrinsic reaction catalyst and a solvent. Merits of this reaction are self-catalysis, easy workup process, less reaction time, and environmental friendliness.