The photodynamics of six types of indole-based squaraines (SQs) molecules deposited onto quartz substrates by using the spin-coating method have been studied by means of steady-state and time-resolved techniques. Enhanced scattering signal at the resonance wavelengths together with the broadening and shift of the absorption bands to the red side with respect to those in solution prove the formation of H-and J-aggregates in the thin film samples. Excited state deactivation dynamics were studied by the femtosecond (fs) transient absorption spectroscopy and nanosecond (ns) flash photolysis. Faster kinetics were obtained for the solid state samples as compared to those in solution. Singular value decomposition (SVD) analysis of the fs transient signal proves the presence of monomers and aggregates, enabling the separation of the kinetics for each one. For the SQ monomers, the dynamics of the singlet excited state does not depend on the pump fluence, and we thus propose that the quenching of the excited monomers is due to an energy transfer process to the aggregates. For the SQ aggregates, nonexponential fit of the experimental time profiles along with the power dependence of the transient absorption signal indicates a singlet− singlet annihilation process (γ′ ≈ 3 × 10 −15 cm 3 s −1/2 ). The combination of the long-range Forster-type mechanism and quantum delocalization is found to be the physical process that accounts for the singlet−singlet annihilation. In the flash photolysis experiments, we observed transient signals with a maximum intensity at 710 nm and lifetimes of 30 and 35 ns for SQ 41 and SQ 26, respectively. We have attributed these signals to the cis photoisomers of the aggregates deactivating to the trans photoisomers through the back photoisomerization reaction. These results provide information for a better understanding of the photodynamics of squaraines.

We present femto-to-millisecond studies of the photodynamics of seven types of indole-based squaraine molecules (SQs) in solvents of different H-bonding ability and viscosity. These SQs can be classified into two families: SQs with two carboxylic groups in the side indole groups (symmetrical SQs) and with only one carboxylic group (asymmetrical SQs). Steady-state absorption and fluorescence techniques show narrow absorption and emission bands, with a small Stokes shift (about 300 cm(-1)). The femtosecond transient absorption spectra give a very short (∼100 fs) dynamics (assigned to IVR) and the associated spectra show two excited species assigned to two stereoisomers. A trans-cis photoisomerization occurs in a very fast time through a conical intersection. Pico-to-nanosecond emission experiments also reveal the presence of two fluorescing trans stereoisomers whose lifetimes show similar sensitivities to the nature of solvent. For example, lifetimes of 1.72, 0.46 and 0.29 ns were determined for the trans photoisomer of the SQ 41 in triacetin, dichloromethane and acetonitrile, respectively, reflecting the short decay of the S(1) state in highly polar and low viscous solvents. Flash photolysis experiments gave the transient absorption signals of the cis photoisomer that is formed after the twisting process at S(1). The cis-to-trans photoisomerization at the ground state happens in the μs time scale (1-4 μs), and it depends on the H-bonding ability and viscosity of the solvent. Thus, combining fs-ns and ns-μs experiments suggests that in the conical intersection region, only a small fraction of the twisted trans isomers are converted to the cis ones in the excited states. These results bring detailed and global insight into the large time window photodynamics of this family of SQs in solution.

Eisenia lucens is an earthworm living in the organic soil layer of decomposing wood. When irritated, the worm expels coelomic fluid through pores in its body wall, exhibiting blue-green bioluminescence. The mechanism of the bioluminescence, which seems to be different from other bioluminescence systems of terrestrial animals, has been studied in this work. Many lines of evidence indicate that riboflavin stored in coelomycetes plays an important role in this glowing reaction.

A xanthene derivative, Granada Green dinitrobenzene sulfonate (GGDNBS), has been synthesized to assay cellular oxidative stress based on changes in the concentration of biothiols. The dye is able to react with biological thiols by a thiolysis reaction that promotes a change in fluorescence intensity. To demonstrate the usefulness of GGDNBS for in vivo oxidative stress measurements, 661 W photoreceptor-derived cells were exposed to light to induce ROS generation, and changes in GGDNBS fluorescence were measured. In these cells, GGDNBS fluorescence was correlated with the biothiol levels measured by an enzymatic method. Therefore, GGDNBS allows us to monitor changes in the levels of biothiols associated with ROS generation via single-cell bioimaging.

Solvation is an important phenomenon, especially in association with heterogeneous phase interactions. Coumarin C522, C(14)H(12)NO(2)F(3), is used as a fluorophore probe to study the interaction between coumarin and a reduced-charge montmorillonite (RCM) surface. Such hydrophilic and hydrophobic interactions are of interest for sorption processes in confined environments. The prepared RCM series with 0.00, 0.12, 0.26, 0.43, 0.66, and 0.97 Li(+) molar fractions provide different surface charges. The aqueous dispersion of the C522/water/RCM system is studied by using steady-state and time-resolved fluorescence spectroscopies. Both the Stokes shift and the dynamics of the solvation process varied as a function of surface charge. Steady-state fluorescence spectroscopy reveals that the C522 Stokes shift varies from 5,115 cm(-1) for the 0.00 Li(+) molar fraction to 3,988 cm(-1) for the 0.97 Li(+) molar fraction. Time-resolved fluorescence spectroscopy determines that the decay time T((1)) varies from 1.0 ps for the 0.00 Li(+) molar fraction to 3.6 ps for the 0.97 Li(+) molar fraction. Within the range of a few picoseconds, the dynamics of the water solvation shell may be described with H-bond rearrangement, modified with the different RCM surface charges. Two models illustrating the interactions between C522 and RCM in water are proposed which qualitatively describe the dynamics. To the best of our knowledge, this experiment is the first measurement of solvation dynamics on a montmorillonite structure surface using ultrafast laser fluorescence spectroscopy.