Ultrafast time-resolved photoluminescence from novel metal–dendrimer nanocomposites

We report the first results of ultra-fast enhanced light emission from gold– and silver–dendrimer nanocomposites. There is a fast (70 fs) fluorescence decay component associated with the metal nanocomposites. Anisotropy measurements show that this fast component is depolarized. The enhanced emission is suggestively due to local field enhancement in the elongated metal–dendrimer nanoparticles. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71043/2/JCPSA6-114-5-1962-1.pd

Two-Photon Fluorescence Spectroscopy and Imaging of 4-Dimethylaminonaphthalimide Peptide and Protein Conjugates

We report detailed photophysical studies on the two-photon fluorescence processes of the solvatochromic fluorophore 4-DMN as a conjugate of the calmodulin (CaM) and the associated CaM-binding peptide M13. Strong two-photon fluorescence enhancement has been observed which is associated with calcium binding. It is found that the two-photon absorption cross-section is strongly dependent on the local environment surrounding the 4-DMN fluorophore in the CaM conjugates, providing sensitivity between sites of fluorophore attachment. Utilizing time-resolved measurements, the emission dynamics of 4-DMN under various environmental (solvent) conditions are analyzed. In addition, anisotropy measurements reveal that the 4-DMN–S38C–CaM system has restricted rotation in the calcium-bound calmodulin. To establish the utility for cellular imaging, two-photon fluorescence microscopy studies were also carried out with the 4-DMN-modified M13 peptide in cells. Together, these studies provide strong evidence that 4-DMN is a useful probe in two-photon imaging, with advantageous properties for cellular experiments.German Science Foundation (SO 1100/1-1

Detection of TNT using a sensitive two-photon organic dendrimer for remote sensing

"There is currently a need for superior stand-off detection schemes for protection against explosive weapons of mass destruction. Fluorescence detection at small distances from the target has proven to be attractive. A novel unexplored route in fluorescence chemical sensing that utilizes the exceptional spectroscopic capabilities of nonlinear optical methods is two-photon excited fluorescence. This approach utilizes infra-red light for excitation of remote sensors. Infra-red light suffers less scattering in porous materials which is beneficial for vapor sensing and has greater depth of penetration through the atmosphere, and there are fewer concerns regarding eye safety in remote detection schemes. We demonstrate this method using a novel dendritic system which possesses both excellent fluorescence sensitivity to the presence of TNT with infra-red pulses of light and high two-photon absorption (TPA) response. This illustrates the use of TPA for potential stand-off detection of energetic materials in the infra-red spectral regions in a highly two-photon responsive dendrimer."http://deepblue.lib.umich.edu/bitstream/2027.42/64171/1/nano8_11_115502.pd

Evolution of the Dynamics of As-Deposited and Annealed Lead Halide Perovskites

The rapid rise of organolead trihalide perovskites as solar photovoltaic materials has been followed by promising developments in light-emitting devices and lasers due to their unique and promising optical properties. Evolution of the photophysical properties in as-deposited or annealed CH₃NH₃PbBr₃ and CH₃NH₃PbI₃ perovskite films processed through the interdiffusion method has been investigated. Absorption spectra showed broad band edge saturation in the as-deposited films in contrast to sharp excitonic absorption in the annealed films. Fluorescence emission of the perovskite films showed strong dependence on the halogen type with a very high quantum yield of ∼90% for the annealed CH₃NH₃PbBr₃ film. An explanation for this was provided based on its crystallinity and quantum confinement of the excitons. The emission showed weakly Stokes shifted bands. Time-resolved spectroscopic measurements were carried out to probe the ultrafast dynamics for the perovskites for the as-deposited or annealed films. We classified the evolution in the absorption features in the excited state of CH₃NH₃PbBr₃ perovskite films for the first time and compared them to CH₃NH₃PbI₃. We suggest a bleach feature below 400 nm as the charge transfer band, which results in the photoinduced absorption in the CH₃NH₃PbBr₃ perovskite film, a charge-separated band gap state, and the existence of intermediate excited-state species that regenerate the ground state

Two-Photon Fluorescence Spectroscopy and Imaging of 4‑Dimethylaminonaphthalimide Peptide and Protein Conjugates

We report detailed photophysical studies on the two-photon fluorescence processes of the solvatochromic fluorophore 4-DMN as a conjugate of the calmodulin (CaM) and the associated CaM-binding peptide M13. Strong two-photon fluorescence enhancement has been observed which is associated with calcium binding. It is found that the two-photon absorption cross-section is strongly dependent on the local environment surrounding the 4-DMN fluorophore in the CaM conjugates, providing sensitivity between sites of fluorophore attachment. Utilizing time-resolved measurements, the emission dynamics of 4-DMN under various environmental (solvent) conditions are analyzed. In addition, anisotropy measurements reveal that the 4-DMN–S38C–CaM system has restricted rotation in the calcium-bound calmodulin. To establish the utility for cellular imaging, two-photon fluorescence microscopy studies were also carried out with the 4-DMN-modified M13 peptide in cells. Together, these studies provide strong evidence that 4-DMN is a useful probe in two-photon imaging, with advantageous properties for cellular experiments

Structure and Dynamics of the ¹(TT) State in a Quinoidal Bithiophene: Characterizing a Promising Intramolecular Singlet Fission Candidate

Tetracyanoquinodimethane bithiophene (QOT2) has a long-lived (57 μs) photoinduced excited state that may correspond to triplets resulting from intramolecular singlet fission (SF). Since SF usually occurs through intermolecular processes, a detailed description of the excited states involved and their evolution is needed to verify this hypothesis. The photoresponse of QOT2 is investigated using high-level electronic structure methods and quantum dynamics simulations, which show ultrafast passage through a conical intersection from the bright 1¹B_u state to the dark 2¹A_g surface. Characterization of QOT2’s 2¹A_g wave function found it to be composed of two strongly coupled triplets, leading to the first detailed electronic structure description of an intramolecular ¹(TT) state. The population of such a state upon excitation of QOT2 raises the possibility of SF through conformational changes that decouple the triplets. However, reaching an appropriate geometry for decoupled triplets appears unlikely given the energy cost of 1.76 eV. Consequently, the hypothesis that the long-lived excited state corresponds to 2¹A_g, a spin singlet, strongly interacting double triplet, was explored. Transition moment calculations to assign excited-state absorption signals and investigations into internal conversion and intersystem crossing decay pathways indicate that a long-lived 2¹A_g state with ¹(TT) character is consistent with the available experimental data