Palladium phthalocyanine (PdPc) covalently bonded to the internal framework of MCM-41 mesoporous structured silicates has been synthesized and studied by UV-vis steady-state absorption and fluorescence spectroscopy, and by pico-and femtosecond time-resolved emission spectroscopy in dichloromethane suspensions. We compare the results obtained for covalently bonded (MO-PdPc) and diffusion-formed (PdPc_MCM41) samples. A significant broadening of the diffuse transmittance spectra of both materials is observed. The effect is due to electrostatic and specific (through H-bonds) interactions of the guest with the host, but to some extent, formation of dimers also contributes to this broadening. However, only the MO-PdPc shows an additional absorption band around 708 nm. The static emission spectrum of MO-PdPc is different from that of PdPc, but it is similar to that of the metal-free phthalocyanine one. The results are explained in terms of confinement effect of the mesoporous material inducing deformation of the phthalocyanine molecule, and probably to the involvement of a photoinduced and reversible metal ejection process. The rise of new 1.4-ns component in the time-correlated single-photon counting emission decays of MO-PdPc reflects the nature of the confinement effect on the lifetimes of the guest. The ultrafast (fs regime) emission measurements show moderate dependence of the observed times on the type of inclusion (covalently bonded versus nonbonded). The origin of these times, ∼170 -500 fs and 1.5 -4.4 ps, is discussed according to the previous findings and nature of the nanosystem.

A new method for extending the utilizable range of Förster resonance energy transfer (FRET) is proposed and tested by the Monte Carlo technique. The obtained results indicate that the efficiency of FRET can be significantly enhanced at a given distance if the energy transfer takes place toward multiple acceptors that are closely located on a macromolecule instead of a single acceptor molecule as it is currently used in FRET analysis. On the other hand, reasonable FRET efficiency can be obtained at significantly longer distances than in the case of a single acceptor. Randomly distributed and parallel orientated acceptor transition moments with respect to the transition moment of the donor molecule have been analyzed as two extreme cases. As expected, a parallel orientation of donor and acceptor transition moments results in a more efficient excitation energy transfer. This finding could be used to directly reveal the assembly/deassembly of large protein complexes in a cell by fluorescence microscopy.

No abstract

The relaxation dynamics of 5,10,15,20-tetrakis(4-hydroxyphenyl)-porphyrin (p-THPP) in tetrahydrofuran (THF) and encapsulated within the human serum albumin (HSA) protein in water solution was investigated. The protein environment affects the B→Q(y) and Q(x)→Q(y) transition dynamics (from 80 and 140-200 fs in THF to 50 and 100 fs in HSA, respectively) as well as the lifetime of the relaxed Q(x) state (9.1 vs 9.9 ns). The most prominent differences are observed in the relaxation dynamics in the hot Q(x) state in HSA, which includes the energy transfer to the protein in ∼1 ps and much slower solvent-assisted thermal equilibration component of about 20-30 ps.

No abstract

The present work describes synthesis, characterization, and use of a new dansyl-labelled Ag@SiO2 nanocomposite as an element of a new plasmonic platform to enhance the fluorescence intensity. Keeping in mind that typical surface plasmon resonance (SPR) characteristics of silver nanoparticles coincide well enough with the absorption of dansyl molecules, we used them to build the core of the nanocomposite. Moreover, we utilized 10 nm amino-functionalized silica shell as a separator between silver nanoparticles and the dansyl dye to prevent the dye-to-metal energy transfer. The dansyl group was incorporated into Ag@SiO2 core-shell nanostructures by the reaction of aminopropyltrimethoxysilane with dansyl chloride and we characterized the new dansyl-labelled Ag@SiO2 nanocomposite using transmission electron microscopy (TEM) and Fourier-transform infrared spectroscopy (FTIR). Additionally, water wettability measurements (WWM) were carried out to assess the hydrophobicity and hydrophilicity of the studied surface. We found that the nanocomposite deposited on a semitransparent silver mirror strongly increased the fluorescence intensity of dansyl dye (about 87-fold) compared with the control sample on the glass, proving that the system is a perfect candidate for a sensitive plasmonic platform.

No abstract

Thin films of rhodamine 6G in titanium dioxide (Rh6G/TiO 2 ) and silicon dioxide (Rh6G/SiO 2 ) were synthesized using the sol−gel method. We explored two kinds of matrices as hosts for rhodamine 6G (Rh6G) at different concentrations of the dye. The pronounced effect of the dye concentration on the absorption and fluorescence spectra as well as on time-resolved fluorescence spectra was found. In particular, it was found that the aggregation of the guest dye is significantly weaker in the Rh6G/TiO 2 nanolayer. The absence of an isosbestic point in absorption spectra in a silica matrix suggests the formation of higher order aggregates, whereas the changes of absorption profile in Rh6G/TiO 2 matrix indicate the formation of dimers. Rh6G aggregates are strongly fluorescent in Rh6G/TiO 2 nanolayer, which can be seen from time-resolved and steady-state emission spectra. For Rh6G/SiO 2 nanolayers these changes are much less pronounced and concern mostly the red shift of the fluorescence maximum.