Shantaram Kothavale

A new type of triphenylamine based coumarin–rhodamine hybrid compound: synthesis, photophysical properties, viscosity sensitivity and energy transfer

A series of novel core modified triphenylamine coumarin–rhodamine systems (compounds MCMR, MCDR and DCMR) was designed and synthesized by incorporating a coumarin moiety on one and a rhodamine moiety on the other phenyl ring of the triphenylamine molecular skeleton. The resulting dyes possessed the individual advantages of coumarin and rhodamine derivatives to show high fluorescence in their spirocyclic and open form respectively. Positive solvatochromism observed in the spirocyclic form is well supported by a linear (Lippert–Mataga and Mac-Rae) and a multi-linear regression analysis (Kamlet–Taft and Catalan parameters) suggesting that for all three compounds solvent polarizability and solvent dipolarity are the main factors responsible for their slightly red shifted absorption spectra, and highly red shifted emission spectra. The viscosity studies are indicative of the induced fluorescence enhancement of open form rhodamine derivatives over the viscosity insensitive rigid lactone ring of spirocyclic form of rhodamine derivatives. In the present studies compound MCMR in its open form when excited at 440 nm shows through space energy transfer from coumarin donor to rhodamine acceptor. This design strategy is straightforward and adaptable to various deep red dyes by simply modifying the core of different fluorophores, thereby generating a through space energy transfer systems.

Novel triphenylamine based rhodamine derivatives: synthesis, characterization, photophysical properties and viscosity sensitivity

Five novel triphenylamine based deep red to NIR emitting rhodamine derivatives were synthesized and characterized by 1H and 13C NMR spectroscopy and elemental analysis. The photophysical properties of all these derivatives were studied in their spirocyclic as well as open form. Hydroxyl substituted derivatives were found to show red shifted emissions as compared to the plain rhodamine derivatives, while triphenylamine substituted derivatives showed larger Stokes shift and emission in the NIR region. All these newly synthesized rhodamine derivatives show comparatively larger Stokes shift (44–135 nm) than the commercially available Rhodamine B and Rhodamine 101. In their open form they are found to exhibit different emission color from pink (619 nm) to dark blue (719 nm) in day as well as UV-light. We also studied the interconversion of dye RH-2 from its spirocyclic to open form with the addition of acid (TFA in toluene). They are studied for their viscosity sensitivity and found to show very high fluorescence enhancement in polar viscous media such as ethanol–glycerol in their open form.

Triphenylamine Derived 3-Acetyl and 3-Benzothiazolyl Bis and Tris Coumarins: Synthesis, Photophysical and DFT Assisted Hyperpolarizability Study

Triphenylamine derived bis- and tris-branched donor-pi-acceptor coumarins with acetyl and benzothiazolyl acceptors are studied for their linear and nonlinear optical properties that originate from their photophysical and molecular structure. Plots of solvent polarities versus the Stokes shift, frontier molecular orbital analysis and Generalised Mulliken Hush analysis have established their strong charge transfer character supported by the strong emission solvatochromism of these chromophores. On the basis of excited state intramolecular charge transfer, the first-, second- and third-order polarizability of these dyes are determined by a solvatochromic method and supported by density functional theory calculations using CAM-B3LYP/6-31g(d). Compared to the acetyl group, the benzothiazolyl group is a strong acceptor, and its corresponding derivatives show enhanced absorption, emission maxima and non-linear optical response. Bond length alternation and bond order alternation analysis reveals that these chromophores approach the cyanine-like framework which is responsible for maximum perturbation to produce high nonlinear optical response. Third order nonlinear susceptibility for dyes 1 and 2 is determined by Z-scan measurement. All of these methods are used to determine the nonlinear optical properties, and thermogravimetric analysis suggests that these chromophores are thermally robust and efficient nonlinear optical materials.

Proton Induced Modulation of ICT and PET Processes in an Imidazo-phenanthroline Based BODIPY Fluorophores

BODIPY fluorophores linked with an imidazo-phenanthroline donor at α and β positions have been synthesized. Intriguing intramolecular charge transfer phenomenon is observed in both the dyes which has been extensively investigated using UV–vis absorption, steady-state and time-resolved fluorescence measurements. H-bonding and intrinsic polarity of the solvents has modulated the absorption and emission bands of these fluorophores strongly causing significant increase in the Stokes shifts. In spite of having difference only in terms of the position of donor subunit, the photophysics of these dyes are not only significantly different from each other, but contradictory too. Interestingly, acidochromic studies revealed the shuttling mechanism between ICT and PET processes for BDP 2. Quantum chemical calculations have been employed further to support experimental findings. DFT and TD-DFT method of analysis have been used to optimize ground and excited state geometries of the synthesized dyes.

Synthesis of novel carbazole based styryl: rational approach for photophysical properties and TD-DFT.

The synthesis and solvatochromic behavior of four novel carbazole based fluorescent styryl dyes were explained. In chlorinated solvents such as DCM and chloroform, these dyes show bathochromic shift in their absorption as well as emission. The styryl dyes 6b and 6c show solid state yellow fluorescence. DFT and TD-DFT computations were performed to study structural, molecular, electronic and photophysical properties of these dyes. The computed absorption and emission wavelength values are found to be in good agreement with the experimental results. The photophysical properties of these 1-styryl carbazole dyes are also compared with the recently reported 3-styrl carbazole dyes. The unique behavior of dye 6d is well explained by its optimized geometry found in the excited state. Ratio of ground to excited state dipole moment of the synthesized novel styryl compounds were calculated by Bakhshiev and Bilot-Kawski correlations.