We report on photophysical studies of lumichrome (Lc) in water at different pHs, and interacting with the human serum albumin (HSA) protein and β-cyclodextrin (β-CD) in neutral aqueous solutions. We used steady-state and picosecond time-resolved emission spectroscopy to investigate the structural changes of Lc at the ground and excited states, as well as the rotational dynamics of the complexes with HSA and β-CD. In neutral water, the predominant neutral alloxazine-type structure of Lc coexists with a small population of the anionic form. In the presence of HSA, we observed an increase in the absorption band intensity at 450 nm. This increase is due to a preferential complexation (1:1 stoichiometry, K=8600 M(-1)) of the Lc anion structures within the protein. This change is not observed when β-CD is added, in which the Lc neutral form is exclusively complexed, giving a 1:1 stoichiometry. The fluorescence lifetimes of Lc in neutral water solutions are 4.2 and 2.3 ns, assigned to anionic and neutral alloxazinic forms, respectively. Using β-CD, the lifetime of the 1:1 complexes is 0.74 ns, while in the case of HSA complexes we observed two lifetimes (0.83 and 0.14 ns), which we explained in terms of different interactions of the anions with the protein. The rotational relaxation time of free Lc in neutral water is 75 ps. For Lc:β-CD complexes this time is 0.44 ns, in full agreement with the expected value from the hydrodynamic theory. For HSA solutions, we obtained a distribution of values between ∼1 and 4.5 ns, suggesting a site heterogeneity of complexation and a different strength of binding for the involved Lc anionic forms. Our results give information about the different photorelaxation behavior of Lc within chemical and biological cavities, and might help in a better design of nanosystems for drug carriers and delivery.

We report on femto-to nanosecond emission studies of the interaction of an organic dye (TPC1) for solar cells, of (electron-donor)À(π-spacer)À(electron-acceptor) structure, with different semiconductor particles and aluminum-doped MCM-41 silicate mesoporous material, in a dichloromethane (DCM) suspension. We used ZnO, ZrO 2 , and Al 2 O 3 nanoparticles employed in dye-sensitized solar cells as active electron collection materials or insulating layers. Steady-state absorption and emission spectra reflect strong complex formation between TPC1 and the used materials. The femto-to nanosecond emission transients of the interfacial systems show a nonexponential behavior with an averaged half lifetime of 4, 11, and 150 ps for ZnO, ZrO 2 , and Al 2 O 3 , respectively. For the latter, we observed the effect of the dye's concentration indicating the action of a fluorescence self-quenching mechanism. For ZnO and ZrO 2 samples, the lifetime of the complexes is determined by an electron injection rate to the conduction band and trap states of these semiconductor samples. The electron injection does not occur efficiently from the high vibrational levels of TPC1 at the S 1 state, and the subpicosecond dynamics is dominated by solvation with a time similar to that of TPC1/DCM (1.4 ps). It is in contrast with the previously observed strong emission quenching of the hot S 1 state when interacting with titania. We observed a remarkable very efficient deactivation of excited TPC1 (with half-lifetime of 1.5 ps) when interacting with Al-doped MCM-41, probably due to an electron transfer from the dye to the aluminum-doped silica framework having an acid character, and a different Al orbital configuration than that of Al 2 O 3 . We believe that the results presented here will enable a better understanding of the interaction of organic dyes with the surface of nanomaterials used in photovoltaics and help in exploring alternative charge-collective materials for the solar cell improvements.

In this paper, we address femto-to millisecond transient absorption studies of TiO 2 nanoparticle (NP) thin films sensitized with four squaraine (SQ) molecules, with and without a deaggregating agent, chenodeoxycholic acid (CDCA). On the femto-to picosecond time scale, we determined the presence of three transient species by using singular value decomposition (SVD) analysis, i.e., S 1 of the SQ monomers, S 1 of the SQ Haggregates, and the SQ radical cation formed after the electron injection. Both monomers and H-aggregates are proven to inject electrons to the TiO 2 conduction band, being 5 times faster in the monomers (e.g., k ei mon = 5.1 × 10 11 s −1 and k ei H-agg = 1.1 × 10 11 s −1 for SQ 41). Besides, the undesired singlet−singlet annihilation is an active process in these samples, constituting the drain of a high percentage of the absorbed photons. The coadsorption of CDCA on the TiO 2 NP avoids the formation of H-aggregates, and therefore, only two transient species are present in these samples: S 1 of the monomer and the SQ radical cation with k ei mon = 6.7 × 10 11 s −1 for SQ 41. On the microsecond scale, we only observed the transient feature of the radical cation of the SQ that permits one to study its recombination dynamics. Similar lifetimes (94− 150 μs) of the four SQ radial cations are obtained when only monomers are present in the sample. In the absence of CDCA, the presence of H-aggregates contributes to shorten the lifetime of the radical cation (e.g., from 110 to 45 μs in the case of SQ 41). This fact can be explained by considering a stronger electronic coupling of H-aggregates/TiO 2 surface with respect to the monomers. These results explore the photodynamics of this family of SQs adsorbed on TiO 2 NP in a very large time window and will enable a better understanding of the influence of aggregates in the kinetics of these SQs used as sensitizers in DSSCs.

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.

A series of dye-sensitized solar cells (DSSCs) has been prepared by using indole-based or quinoline-based squaraines (SQs) as the sensitizer and containing the commonly used I3 –/I– redox pair or the lately employed cobalt complexes, [Co(dimethylbipyridine)3]3+/2+, [Co(bipyridine)3]3+/2+, and [Co(phenanthroline)3]3+/2+ redox electrolytes. The photodynamics of the different electron transfer reactions have been investigated by means of the femto- to millisecond pump–probe techniques. In the femtosecond transient absorption experiments, the electron injection rate constants and efficiencies, k ei and φei, were determined for each cell. Larger values of k ei and φei for the indole-based (SQ 8) compared to the quinoline-based (SQ 12) squaraines were obtained (13.2 × 1010 s–1 and 0.95 × 1010 vs 6.9 × 1010 s–1 and 0.81 for SQ 8 or SQ 12 with the I3 –/I– pair, respectively), despite the similar values of the electron injection driving forces (−ΔG 0 ei = 0.75 vs 0.76 eV). This is due to the lower electron density in the lowest unoccupied molecular orbital at the anchoring group (−COOH) in SQ 12 compared to SQ 8. However, the type of electrolyte did not affect the kinetics of the electron injection processes. In the flash photolysis experiments, the kinetic parameters of the electron recombination via dye or electrolyte and the cation regeneration were calculated from the decays of the transient absorption signals of the electrons (1550 nm) or the SQ cation (570 nm). It was found that the electron recombination with the oxidized redox species is faster with the Co-based compared to the I3 –/I– electrolytes for both SQs, τrec = 3 versus ∼0.5–1 ms. This proves that the steric hindrance in these SQs is not sufficient to avoid the approach of the Co3+ species to the surface of the TiO2 nanoparticle. Moreover, the regeneration rate constants and efficiencies, k reg and φreg, are considerably smaller for the cells with the different Co-based electrolytes compared to those with the I3 –/I– pair (i.e., k reg = 30 × 104 vs 8 × 104 M–1s–1 and φreg = 0.96 vs 0.75 with the [Co(dmb)3]3+/2+ for SQ 8). This is explained by the lower regeneration driving force, −ΔG reg, in the Co-based electrolytes (0.3–0.1 eV). Thus, the use of Co-based electrolytes in these two SQs is detrimental to the overall efficiency of the cell, since −ΔG reg values below 0.4 eV do not give complete regeneration efficiency. Finally, we have compared the measured photocurrent with the calculated electron injection and regeneration efficiencies, and we found a good correlation between both parameters.

Kinetics of ground state reactions under restricted geometry conditions have been rationalized generally taking as a basis the Pseudophase Model, whose basic hypothesis is: The distribution of the reactants between the pseudophases is at equilibrium, that is, the rate of the reaction is slow in relation to the rates of entry and exit of the reactant to and from the receptor. However, photochemical reactions are generally very rapid, so the following question emerges: is the Pseudophase Model still applicable to photochemical reactions? To answer this question has been the primary objective of this work in which photochemical reactions in micelles, polymers and cyclodextrins have been reviewed. The lifetime of the fluorophore and the distributions of the quencher and the probe are crucial properties; they must be taken into account to obtain a proper description of the behaviour of a given system. The models of Infelta, Almgren and Quina visualise different scenarios with varied combinations of these properties. It is shown that, in some cases, the Pseudophase Model holds at least formally.

Dye-sensitized solar cells (DSSCs) fabricated with TiO 2 nanoparticle thin films and sensitized with four types of indole-based squaraines, SQs (symmetric or asymmetric and varying the length and nature of the alkyl side chain substituents), have been prepared. We have studied the influence of the presence of different additives in the electrolyte solutions (tert-butyl pyridine and/or Li + cations) on the electron transfer dynamics by means of femtosecond transient absorption spectroscopy and flash photolysis. We obtained the rate constants for the electron injection, k ei = 2, 3, 8, and 14 × 10 10 s −1 , for complete solar cells with an iodide-based electrolyte. The asymmetric SQ showed the largest k ei value, 14 × 10 10 s −1 , in line with a unidirectional flow of electrons from the lowest unoccupied molecular orbital (LUMO) orbital of the SQ to the sub-bandgap states of the TiO 2 , which leads to a more efficient electron injection than that in the symmetric SQs. Addition of tert-butyl pyridine to the electrolyte solution (I − /I 3 − in acetonitrile) causes a 5−10-fold deceleration of the electron injection (for example, τ obs = 2−11 ps in SQ 41). When including the Li + cation together with the tert-butyl pyridine, the injection is still slower than in cells without any additive (τ obs = 2 vs 7 ps in SQ 41), which reflects a stronger influence of the tertbutyl pyridine in the electron injection process. The effective lifetimes for the charge regeneration reaction, τ obs , range from 2 to 25 μs for the complete cells with an iodide-based electrolyte. The fastest regeneration occurs in the SQs with the CF 3 − groups anchored to the side chains and, especially in SQ 26, with two CF 3 − groups. This result suggests that the inductive effect of the CF 3 − groups in the structure of SQ 26 and SQ 41 leads to a higher positive charge density in the π-conjugated system, which promotes a higher local concentration of iodide near the oxidized dye and therefore faster regeneration kinetics. Moreover, addition of Li + cations to the electrolyte accelerates the regeneration reaction, which is ascribed to its interaction with the backbone of the SQ, favoring the approach of the I − species. Using the transient absorption results, we calculated the electron injection efficiency, φ ei , and compared it with the short-circuit current density, J sc , of the complete cells. Thus, in the complete cells sensitized with SQ 41 and SQ 4, φ ei are the highest ones and present comparable values, 0.93 and 0.90, respectively. On the contrary, cells sensitized with SQ 26 and SQ 2 present lower values, 0.47 and 0.75, respectively. A similar tendency is observed for the values of J sc . On the basis of this good correlation (φ ei vs J sc ), we can suggest that the electron injection reaction is partially responsible for the photon losses and derive the reasons why this occurs.

Since 1999, a founding member of Bronx Health REACH, has been actively involved in developing the faith-based initiative-focusing primarily on diabetes prevention and maintenance, nutrition, health disparities education, and fitness, (cand.) Robert Foley Sr., DMin, DD, community activist, one of the founding members of Bronx Health REACH, and the Senior Pastor of Cosmopolitan Church of the Lords Jesus, Bronx, NY, for the past 31 years. A native of Colombia (South America) Carlos Devia, MA, project coordinator for the Faith Based Outreach Initiative of Bronx Health REACH, and serves as the research coordinator for the Institute's National Center on Minority Health and Health Disparity (NCMHD) study in collaboration with the Community Research Committee Rosa Rosen, JD, immigrant from the Dominican Republic and was diagnosed with type-2 diabetes in 1997. Ever since, she has worked as an educator and advocate for communities of color in New York City AbstractThis case study provides a mid-course assessment of the Bronx Health REACH faith-based initiative four years into its implementation. The study uses qualitative methods to identify lessons learned and to reflect on the benefits and challenges of using a community-based participatory approach for the development and evaluation of a faith-based program designed to address health disparities. Key findings concern the role of pastoral leadership, the importance of providing a religious context for health promotion and health equality messages, the challenges of creating a bilingual/bi-cultural program, and the need to provide management support to the lay program coordinators. The study also identifies lessons learned about community-based evaluation and the importance of addressing community concern about the balance between evaluation and program. Finally, the study identifies the challenges that lie ahead, including issues of program institutionalization and sustainability. KeywordsHealth disparities; race/ethnicity; community-based participatory research; faith-based initiatives As part of a multifaceted approach to addressing this problem, the Coalition, which formed in 1999, created a strong faith-based initiative. By early 2007, this initiative was being implemented in 17 churches of various denominations, including Baptist, Episcopalian, Evangelical, Seventh Day Adventist, and Catholic. The congregations range in size from 20 to 1,000 members, totaling roughly 5,000 individuals. The faith-based outreach initiative has two goals: (1) to use the capacity and resources of local faith-based institutions to change the knowledge, attitudes, and behavior of community members concerning health promotion, disease self-management, and navigation of the health care system; and (2) to mobilize clergy and church members to seek changes in law, regulation, and policy to promote equal access to care.In each church, the senior pastor commits to sharing information from the pulpit about health promotion and racial disparities in health. The pastors also agree to select a he...