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Dronpa is a photochromic green fluorescent protein (GFP) homologue used as a probe in super-resolution microscopy. It is known that the photochromic reaction involves cis/trans isomerization of the chromophore and protonation/deprotonation of its phenol group, but the sequence in time of the two steps and their characteristic time scales are still the subject of much debate. We report here a comprehensive UV-visible transient absorption spectroscopy study of the photoactivation mechanism of Dronpa, covering all relevant time scales from ∼100 fs to milliseconds. The Dronpa-2 variant was also studied and showed the same behavior. By carefully controlling the excitation energy to avoid multiphoton processes, we could measure both the spectrum and the anisotropy of the first photoactivation intermediate. We show that the observed few nanometer blue-shift of this intermediate is characteristic for a neutral cis chromophore, and that its anisotropy of ∼0.2 is in good agreement with the reorientation of the transition dipole moment expected upon isomerization. These data constitute the first clear evidence that trans → cis isomerization of the chromophore precedes its deprotonation and occurs on the picosecond time scale, concomitantly to the excited-state decay. We found the deprotonation step to follow in ∼10 μs and lead directly from the neutral cis intermediate to the final state.

Conjugated polymers (CPs) are promising materials for fluorescence imaging application. However, a significant problem in this field is the unexplained abnormally low fluorescence brightness (or number of fluorescence photons detected per one excitation photon) exhibited by most of CP single chains in solid polymer hosts. Here it is shown that this detrimental effect can be fully avoided for short chains of polyfluorene-bis-vinylphenylene (PFBV) embedded in a host polymer matrix of PMMA, if the conjugated backbone is insulated by cyclodextrin rings to form a polyrotaxane (PFBV-Rtx). Fluorescence kinetics and quantum yields are measured for the polymers in liquid solutions, pristine films, and solid PMMA blends. The fluorescence brightness of PFBV-Rtx single chains dispersed in a solid PMMA is very close to that expected for a chain with 100% fluorescence quantum yield, while the unprotected PFBV chains of the same length possess 4 times lower brightness. Despite this, the fluorescence decay kinetics are the same for both polymers, suggesting the presence of static or ultrafast fluorescence quenching in the unprotected polymer. About 80% of an unprotected PFBV chain is estimated to be completely quenched. The hypothesis is that the cyclodextrin rings prevent the quenching by working as 'bumpers' reducing the mechanical forces applied by the host polymer to the conjugated backbone and help retaining its conformational freedom. While providing a recipe for making CP fluorescence bright at the single-molecule level, these results identify a lack of fundamental understanding in the community of the influence of the environment on excited states in conjugated materials.

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Fifty seven rhizobacteria were isolated from rhizospheric soil of wilted tomato plants and among them two strains of rhizobacteria, having better antagonistic and plant growth promoting ability were characterized them as Bacillus amyloliquefaciens DSBA-11 and DSBA-12 based on morphological, biochemical, partial gene sequence analysis of 16S rRNA and fatty acid methyl ester analysis. Antagonistic activity of these strains DSBA-11, DSBA-12 was compared with other Bacillus species such as B. subtilis DTBS-5, B. cereus JHTBS-7, B. pumilus MTCC-7092 strains, against Ralstonia solanacearum race 1, bv 3, phylotype I, inciting bacterial wilt of tomato underin vitro conditions. B. amyloliquefaciens DSBA-11 showed maximum growth inhibition of R. solanacearum (4.91cm 2 ) followed by strains DSBA-12 (3.31cm 2 ) and B. subtilis (3.07 cm 2 ). Moreover, strains DSBA-11 was also have better phosphorus solubilizing ability (42.6 µg/ml) and indole acetic acid (95.4 µg/ml) production than other strains of Bacillus spp. in vitro conditions. Biocontrol efficacy and plant growth ability of these bacterial antagonists was tested against bacterial wilt of tomato cv. Pusa Ruby under glasshouse conditions. Minimum bacterial wilt disease incidenceincultivar Pusa Ruby (17.95%) was recorded in B. amyloliquefaciens DSBA-11followed by B. amyloliquefaciens DSBA-12 after 30 days of inoculation.The bio-control efficacy was higher in B. amyloliquefaciens DSBA -12 treated plants, followed by B. pumilus MTCC-7092.

Synthesis of titanium nanoparticles using pulsed laser ablation of titanium in de-ionized water and isopropanol is reported. In situ growth of nanoparticles was confirmed using Rayleigh scattering in liquid and air ambient. Nucleation and growth of nanoparticles in liquid ambient occurs much faster than in air. Synthesized nanoparticles were characterized using the x-ray diffraction, transmission electron microscopy and photoluminescence measurements. Nanoparticles thus produced are spherical in shape, have crystalline phase with size distribution 5–35 nm and the average size increases with the increase in laser fluence. The colloidal solutions of nanoparticles show broad photoluminescence emission in the range 300–500 nm on optical pumping with 266 nm. A comparative study of titanium plasma in liquid and air is reported to understand the formation of titanium nanoparticles from laser plasma confined in different ambient.

Two-dimensional polarization fluorescence imaging of single light harvesting complexes 2 (LH2) of Rps. acidophila was carried out to investigate the polarization properties of excitation and fluorescence emission simultaneously, at room temperature. In two separate experiments we excited LH2 with a spectrally narrow laser line matched to the absorption bands of the two chromophore rings, B800 and B850, thereby indirectly and directly triggering fluorescence of the B850 exciton state. A correlation analysis of the polarization modulation depths in excitation and emission for a large number of single complexes was performed. Our results show, in comparison to B800, that the B850 ring is a more isotropic absorber due to the excitonic nature of its excited states. At the same time, we observed a strong tendency for LH2 to emit with dipolar character, from which preferential localization of the emissive exciton, stable for minutes, is inferred. We argue that the observed effects can consistently be explained by static energetic disorder and/or deformation of the complex, with possible involvement of exciton self-trapping.

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