Nanocomposites of poly(3-hexylthiophene)-cadmium selenide (P3HT-CdSe) were synthesized by directly grafting vinyl-terminated P3HT onto [(4-bromophenyl)methyl]dioctylphosphine oxide (DOPO-Br)-functionalized CdSe quantum dot (QD) surfaces via a mild palladium-catalyzed Heck coupling, thereby dispensing with the need for ligand exchange chemistry. The resulting P3HT-CdSe nanocomposites possess a well-defined interface, thus significantly promoting the dispersion of CdSe within the P3HT matrix and facilitating the electronic interaction between these two components. The photophysical properties of nanocomposites were found to differ from the conventional composites in which P3HT and CdSe QDs were physically mixed. Solid-state emission spectra of nanocomposites suggested the charge transfer from P3HT to CdSe QDs, while the energy transfer from 3.5 nm CdSe QD to P3HT was implicated in the P3HT/CdSe composites. A faster decay in lifetime further confirmed the occurrence of charge transfer in P3HT-CdSe nanocomposites.

This work explores the sensitization of luminescent lanthanide Tb 3+ and Eu 3+ cations by the electronic structure of zinc sulfide (ZnS) semiconductor nanoparticles. Excitation spectra collected, while monitoring the lanthanide emission bands, reveals that the ZnS nanoparticles act as an antenna for the sensitization of Tb 3+ and Eu 3+ . The mechanism of lanthanide ion luminescence sensitization is rationalized in terms of an energy and charge transfer between trap sites and is based on a semi-empirical model, proposed by Dorenbos and coworkers, 1 -6 to describe the energy level scheme. This model implies that the mechanisms of luminescence sensitization of Tb 3+ and Eu 3+ in ZnS nanoparticles are different; namely Tb 3+ acts as a hole trap, while Eu 3+ acts as an electron trap. Further testing of this model is made by extending the studies from ZnS nanoparticles to other II-VI semiconductor materials; namely, CdSe, CdS, and ZnSe.

The potential use of the naturally occurring yellow-orange pigment curcumin as a photodynamic therapy agent is one of the most exciting applications of this medicinal compound. Although subnanosecond spectroscopy has been used to investigate the photophysical processes of curcumin, the time resolution is insufficient to detect important and faster photoinduced processes, including solvation and excited-state intramolecular hydrogen atom transfer (ESIHT). In this study, the excited-state photophysics of curcumin is studied by means of ultrafast fluorescence upconversion spectroscopy. The results show two decay components in the excited-state kinetics with time scales of 12−20 ps and ∼100 ps in methanol and ethylene glycol. The resulting prominent isotope effect in the long component upon deuteration indicates that curcumin undergoes ESIHT in these solvents. The short component (12−20 ps) is insensitive to deuteration, and multiwavelength fluorescence upconversion results show that this decay component is due to solvation of excited-state curcumin. KeywordsAtomic spectroscopy, deuterium, ethylene, ethylene glycol, fluorescence, free radical reactions, hydrogen, methanol, photodynamic therapy, solvation, curcumin, decay components, deuteration, excited-state, fluorescence upconversion, intramolecular hydrogens, isotope effects, photophysics The potential use of the naturally occurring yellow-orange pigment curcumin as a photodynamic therapy agent is one of the most exciting applications of this medicinal compound. Although subnanosecond spectroscopy has been used to investigate the photophysical processes of curcumin, the time resolution is insufficient to detect important and faster photoinduced processes, including solvation and excited-state intramolecular hydrogen atom transfer (ESIHT). In this study, the excited-state photophysics of curcumin is studied by means of ultrafast fluorescence upconversion spectroscopy. The results show two decay components in the excited-state kinetics with time scales of 12-20 ps and ∼100 ps in methanol and ethylene glycol. The resulting prominent isotope effect in the long component upon deuteration indicates that curcumin undergoes ESIHT in these solvents. The short component (12-20 ps) is insensitive to deuteration, and multiwavelength fluorescence upconversion results show that this decay component is due to solvation of excited-state curcumin.

An analysis is provided of the subnanosecond dynamic solvation of ionic liquids in particular and ionic solutions in general. It is our hypothesis that solvation relaxation in ionic fluids, in the nonglassy and nonsupercooled regimes, can be understood rather simply in terms of the dielectric spectra of the solvent. This idea is suggested by the comparison of imidazolium ionic liquids with their pure organic counterpart, butylimidazole (J. Phys. Chem. B 2004, 108, 10245-10255). It is borne out by a calculation of the solvation correlation time from frequency dependent dielectric data for the ionic liquid, ethylammonium nitrate, and for the electrolyte solution of methanol and sodium perchlorate. Very good agreement is obtained between these theoretically calculated solvation relaxation functions and those obtained from fluorescence upconversion spectroscopy. Our comparisons suggest that translational motion of ions may not be the predominant factor in short-time solvation of ionic fluids and that many tools and ideas about solvation dynamics in polar solvents can be adapted to ionic fluids.

Steady-state and time-resolved Stokes shift data for the probe coumarin 153 in two imidazoles, six imidazolium-based ionic liquids, and several other solvents are presented. These results are consistent with our original suggestion (J. Phys. Chem. B 2004, 108, 10245−10255) that initial solvation is dominated by the organic moiety of the ionic liquid, and they show that for the imidazole-based liquids initial solvation is in all cases very rapid. Solvation by methylimidazole and butylimidazole is complete in 100 ps, and all of the imidazolium ionic liquids demonstrate similarly rapid initial solvation. Owing to the importance of determining the amount of initial solvation that is missed in a given experiment with finite time resolution, we discuss a method of estimating the intramolecular contribution to the reorganization energy. This method yields 2068 cm-1 and is compared with an alternative method. ReceiVed: February 1, 2006; In Final Form: May 18, 2006 Steady-state and time-resolved Stokes shift data for the probe coumarin 153 in two imidazoles, six imidazoliumbased ionic liquids, and several other solvents are presented. These results are consistent with our original suggestion (J. Phys. Chem. B 2004, 108, 10245-10255) that initial solvation is dominated by the organic moiety of the ionic liquid, and they show that for the imidazole-based liquids initial solvation is in all cases very rapid. Solvation by methylimidazole and butylimidazole is complete in 100 ps, and all of the imidazolium ionic liquids demonstrate similarly rapid initial solvation. Owing to the importance of determining the amount of initial solvation that is missed in a given experiment with finite time resolution, we discuss a method of estimating the intramolecular contribution to the reorganization energy. This method yields 2068 cm -1 and is compared with an alternative method.

We describe a novel method for creating luminescent lanthanide-containing nanoparticles in which the lanthanide cations are sensitized by the semiconductor nanoparticle’s electronic excitation. In contrast to previous strategies, this new approach creates such materials by addition of external salt to a solution of fully formed nanoparticles. We demonstrate this post-synthetic modification for the lanthanide luminescence sensitization of two visible emitting lanthanides (Ln), Tb3+ and Eu3+ ions, through ZnS nanoparticles in which the cations were added post-synthetically as external Ln(NO3)3·xH2O salt to solutions of ZnS nanoparticles. The post-synthetically treated ZnS nanoparticle systems display Tb3+ and Eu3+ luminescence intensities that are comparable to those of doped Zn(Ln)S nanoparticles, which we reported previously (J. Phys. Chem. A, 2011, 115, 4031–4041). A comparison with the synthetically doped systems is used to contrast the spatial distribution of the lanthanide ions, bulk versus surface localized. The post-synthetic strategy described in this work is fundamentally different from the synthetic incorporation (doping) approach and offers a rapid and less synthetically demanding protocol for Tb3+:ZnS and Eu3+:ZnS luminophores, thereby facilitating their use in a broad range of applications.

Electron transfer (ET) in aggregates of cadmium selenide (CdSe) and cadmium telluride (CdTe) nanoparticles (NPs) was studied in aqueous solution by fluorescence quenching. Both steady-state and time-resolved fluorescence measurements were used to quantify how the ET depends on the nature of the NP assemblies. The aggregation of CdSe and CdTe NPs was controlled by the electrostatic attraction of the charged functionalities placed on the NP surface coating. Electron transfer quenching was found to depend on three factors: the interparticle distance, the energetic alignment of the NP bands (hence the size of the NPs), and the direction of the electric field between the NPs, created by their surface charges. Experimental DetailsMaterials and Methods. Selenium powder (99.999%), tellurium powder (99.999%), cadmium chloride (CdCl 2 ; 99%),

This work develops a rationale for effective sensitization of trivalent lanthanide cation (Ln3+) luminescence in a semiconductor nanoparticle by examining the luminescence characteristics of Ln3+ dopants in titanium dioxide nanoparticles [Ti­(Ln)­O2] [Ln = praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), or ytterbium (Yb)], as a representative model system. For excitation of the TiO2 host at 350 nm the intraconfigurational 4f–4f sharp luminescence bands are observed for the Nd, Sm, Eu, Ho, Er, Tm, and Yb incorporated (doped) nanoparticles, and no such luminescence is observed for the Pr, Gd, Tb, and Dy containing nanoparticles. While host sensitized luminescence of lanthanide ions dominate the emission in the Nd and Sm incorporated nanoparticles, the host sensitization effect is less pronounced for the Eu and Yb containing systems, and for the Ho, Er, and Tm doped nanocrystals only a subset of the dopant ions’ luminescence bands is sensitized. The experimental observations of the host sensitized Ln3+ luminescence properties in the [Ti­(Ln)­O2] nanoparticles can be rationalized by considering that the dopant ions act as charge traps in the host lattice and associated environment induced luminescence quenching effects. Using these results, an energy offset between the trap site and the nanoparticle’s band edge that will generate an optimal host sensitized dopant emission is proposed. The approach presented necessarily improves over a combinatorial approach to select the host and dopant moieties, with the benefit of providing physicochemical insight regarding the nature of photophysical processes in a given host (semiconductor nanoparticle)–guest (Ln3+) composite system.