Effect of protonation on the singlet-singlet excited-state absorption of meso-tetrakis(p-sulphonatophenyl) porphyrin

This work reports on the excited singlet-state absorption cross-section spectra of both biprotonated and\ud nonprotonated states of meso-tetrakis(p-sulphonatophenyl) porphyrin obtained by means of the Z-scan\ud technique with white-light continuum pulses. Although our main purpose was to determine these\ud photo-physical parameters in a wide spectral range, we also analyzed the role of accumulative effects\ud arising as consequence of the pulse chirp caused by the group velocity dispersion. This effect leads to\ud apparent changes in the measured excited-state absorption spectra, which can be corrected during the\ud fitting procedure to yield meaningful absorption cross-section values.FAPES

Excited state dynamics of meso-tetra(sulphonatophenyl) metalloporphyrins

The excited state dynamics of Zn2+, Fe3+, and Mn3+ meso-tetra(sulfonatophenyl) porphyrin complexes were investigated with a Z-scan technique at 532 nm using 70 ps and 120 fs single pulses and 200 ns pulse trains of a Q-switched and mode locked laser. We determined the characteristic interconversion and intersystem crossing times, quantum yields of the excited S1 state, and S1 → Sn and T1 → Tn transition cross-sections. The ground state cross-sections were obtained using UV−vis absorption spectroscopy, and a five-energy-level diagram was used to yield the photophysical parameters mentioned previously.FAPES

Characterization of Triplet State of Cyanine Dyes with Two Chromophores Effect of Molecule Structure

Quantum yields (φT) and energies (ET) of the first triplet state T1 for four molecules of cyanine dyes with two chromophores (BCDs), promising photoactive compounds for various applications, for example, as photosensitizers in photodynamic therapy (PDT) and fluorescence diagnostics (FD), were studied in 1-propanol solutions by steady-state and time-resolved optical absorption techniques. BCDs differ by the structure of the central heterocycle, connecting the chromophores. The heterocycle structure is responsible for electron tunneling between chromophores, for which efficiency can be characterized by splitting of the BCD triplet energy levels. It was shown that the increase in the tunneling efficiency reduces ET values and increases φT values. This aspect is very promising for the synthesis of new effective photosensitizers based on cyanine dyes with two interacting chromophores for various applications, including photodynamic therapy

Pulse train fluorescence technique for measuring triplet state dynamics

We report on a method to study the dynamics of triplet formation based on the fluorescence signal produced by a pulse train. Basically, the pulse train acts as sequential pump-probe pulses that precisely map the excited-state dynamics in the long time scale. This allows characterizing those processes that affect the population evolution of the first excited singlet state, whose decay gives rise to the fluorescence. The technique was proven to be valuable to measure parameters of triplet formation in organic molecules. Additionally, this single beam technique has the advantages of simplicity, low noise and background-free signal detection. (C) 2011 Optical Society of AmericaFundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq

Stimulation of Cysteine-Coated CdSe/ZnS Quantum Dot Luminescence by meso-Tetrakis (p-sulfonato-phenyl) Porphyrin

Abstract Interaction between porphyrins and quantum dots (QD) via energy and/or charge transfer is usually accompanied by reduction of the QD luminescence intensity and lifetime. However, for CdSe/ZnS-Cys QD water solutions, kept at 276 K during 3 months (aged QD), the significant increase in the luminescence intensity at the addition of meso-tetrakis (p-sulfonato-phenyl) porphyrin (TPPS4) has been observed in this study. Aggregation of QD during the storage provokes reduction in the quantum yield and lifetime of their luminescence. Using steady-state and time-resolved fluorescence techniques, we demonstrated that TPPS4 stimulated disaggregation of aged CdSe/ZnS-Cys QD in aqueous solutions, increasing the quantum yield of their luminescence, which finally reached that of the fresh-prepared QD. Disaggregation takes place due to increase in electrostatic repulsion between QD at their binding with negatively charged porphyrin molecules. Binding of just four porphyrin molecules per single QD was sufficient for total QD disaggregation. The analysis of QD luminescence decay curves demonstrated that disaggregation stronger affected the luminescence related with the electron-hole annihilation in the QD shell. The obtained results demonstrate the way to repair aged QD by adding of some molecules or ions to the solutions, stimulating QD disaggregation and restoring their luminescence characteristics, which could be important for QD biomedical applications, such as bioimaging and fluorescence diagnostics. On the other hand, the disaggregation is important for QD applications in biology and medicine since it reduces the size of the particles facilitating their internalization into living cells across the cell membrane

Additional file 1: of Stimulation of Cysteine-Coated CdSe/ZnS Quantum Dot Luminescence by meso-Tetrakis (p-sulfonato-phenyl) Porphyrin

The experimental solutions were prepared in phosphate buffer (pH7.3;7.5mM), using Milli-Q quality water. Figure S1. Dynamic light scattering diagram of fresh prepared (CdSe/ZnS)-Cys 558 quantum dots (QD). Figure S2. Luminescence decay curve of freshly prepared (CdSe/ZnS)-Cys 558 QD solution; λex =480nm and λem =558nm. Figure S3. a Normalized optical absorption spectrum of non-protonated TPPS4 . Inset: Normalized optical absorption spectra of the TPPS4 Q-bands (black line) and “aged” QD (red line), and the fluorescence emission spectrum of non-protonated TPPS4 with maximum at 644nm (blue line), λex =515nm. b TPPS4 fluorescence decay kinetics at 650nm, λex =515nm. Figure S4. a Optical absorption spectra of the aged (CdSe/ZnS)-Cys 558 QD and TPPS4 mixture at different TPPS4 concentrations. Inset: Details of the absorption spectra in the region of the porphyrin Q-bands. b Optical absorption spectra just for TPPS4 in the mixture TPPS4 +QD. The final spectrum of each sample was obtained subtracting the initial QD absorption spectrum (no TPPS4 adding). c Details of the absorption spectra in the region of the porphyrin Qbands, showing that TPPS4 absorption spectrum does not change in the presence of aged (CdSe/ZnS)-Cys 558 QD. The curves for 0.1 and 0.3μM of TPPS4 are not shown due to the lower signal-to-noise ratio of Qbands. No significant spectral shift was observed either Soret or Q-bands. Figure S5. a Normalized fluorescence excitation spectra of TPPS4 in Milli-Q quality water as a function of TPPS4 concentrations, λem =646nm. b Luminescence excitation spectra of TPPS4 and aged (CdSe/ZnS)-Cys 558 QD mixtures as a function of TPPS4 concentrations; λem =646nm; [QD]=570nM. Figure S6. a Zeta-potential measured on Malvern ZETASIZER 3000HSA (λex =633nm, 10mW HeNe laser) a aged QD (ξaged-QD) and b TPPS4 porphyrin (ξTPPS4). Table S1. Variation of aged (CdSe/ZnS)-Cys 558 QD hydrodynamic diameter (Dhd) as a function of its concentration measured on NanoBrook 90Plus Zeta Particle Size Analyzer (λex =640nm, 40mW HeNe laser). (PDF 524 kb

Experimental and theoretical study of two-photon absorption in nitrofuran derivatives: Promising compounds for photochemotherapy

We report experimental and theoretical studies of the two-photon absorption spectrum of two nitrofuran derivatives: nitrofurantoine, (1-(5-nitro-2-furfurilideneamine)-hidantoine) and quinifuryl, 2-(5`-nitro-2`-furanyl) ethenyl-4-{N-[4`-(N,N-diethylamino)-1`-methylbutyl]carbamoyl} quinoline. Both molecules are representative of a family of 5-nitrofuran-ethenyl-quinoline drugs that have been demonstrated to display high toxicity to various species of transformed cells in the dark. We determine the two-photon absorption cross-section for both compounds, from 560 to 880 nm, which present peak values of 64 GM for quinifuryl and 20 GM for nitrofurantoine (1 GM = 1 x 10(-50) cm(4).s.photon(-1)). Besides, theoretical calculations employing the linear and quadratic response functions were carried out at the density functional theory level to aid the interpretations of the experimental results. The theoretical results yielded oscillator strengths, two-photon transition probabilities, and transition energies, which are in good agreement with the experimental data. A higher number of allowed electronic transitions was identified for quinifuryl in comparison to nitrofurantoine by the theoretical calculations. Due to the planar structure of both compounds, the differences in the two-photon absorption cross-section values are a consequence of their distinct conjugation lengths. (c) 2011 American Institute of Physics. [doi:10.1063/1.3514911