Unsymmetrical Relaxation Paths of the Excited States in Cyanine Dyes Detected by Time-Resolved Fluorescence:Polymethinic and Polyenic Forms

Novel applications of organic dyes and vast opportunities for their molecular tailoring keep focus of scientific community on the issues of symmetry breaking in the systems having different location of uncompensated charge, which has tremendous impact on photoluminescent properties of the dyes. In this paper, we provide distinctive experimental evidences of three relaxation paths (one symmetrical and two unsymmetrical) of excited states by analysis of lifetime and spectra of time-resolved fluorescence at low temperature with strong support of quantum-chemical modeling. Importantly, the studied cyanine dye (astraphloxin) in aqueous solution has two different unsymmetrical relaxation paths of excites states in the polymethinic and donor-acceptor polyenic forms, where the last form strongly diminishes in less polar media. The experimental and computational results provide essential fundamental knowledge of molecular electronic relaxations substantially affected by matrix rigidity and polarity for design and photonic applications of elongated π-electronic systems

Emergence of additional visible range photoluminescence due to aggregation of cyanine dye:astraphloxin on carbon nanotubes dispersed with anionic surfactant

Self-organization of organic molecules with carbon nanomaterials leads to formation of functionalized molecular nano-complexes with advanced features. We present a study of physical and chemical properties of carbon nanotube-surfactant-indocarbocyanine dye (astraphloxin) in water focusing on aggregation of the dye and resonant energy transfer from the dye to the nanotubes. Self-assembly of astraphloxin is evidenced in absorbance and photoluminescence depending dramatically on the concentrations of both the dye and surfactant in the mixtures. We observed an appearance of new photoluminescence peaks in visible range from the dye aggregates. The aggregates characterized with red shifted photoluminescence peaks at 595, 635 and 675 nm are formed mainly due to the presence of surfactant at the premicellar concentration. The energy transfer from the dye to the nanotubes amplifying near-infrared photoluminescence from the nanotubes is not affected by the aggregation of astraphloxin molecules providing important knowledge for further development of advanced molecular nano-complexes. The aggregation with the turned-on peaks and the energy transfer with amplified photoluminescence create powerful tools of visualization and/or detection of the nanotubes in visible and near-infrared spectral range, respectively, boosting its possible applications in sensors, energy generation/storage, and healthcare

Fluorene-Based Metal-Ion Sensing Probe With High Sensitivity To Zn \u3csup\u3e2+\u3c/sup\u3e And Efficient Two-Photon Absorption

The photophysical, photochemical, two-photon absorption (2PA) and metal ion sensing properties of a new fluorene derivative (E)-1-(7-(4-(benzo[d]thiazol-2- yl)styryl)-9,9-bis(2-(2-ethoxyethoxy)ethyl)-9H-fluoren-2-yl)-3-(2-(9,10,16,17, 18,19,21,22,23,24-decahydro-6H dibenzo[h,s][1,4,7,11,14,17] trioxatriazacycloicosin-20(7H)-yl)ethyl)thiourea (1) were investigated in organic and aqueous media. High sensitivity and selectivity of 1 to Zn 2+ in tetrahydrofuran and a water/acetonitrile mixture were shown by both absorption and fluorescence titration. The observed complexation processes corresponded to 1:1 stoichiometry with the range of binding constants ∼(2-3) - 105 M-1. The degenerate 2PA spectra of 1 and 1/Zn 2+ complex were obtained in the 640-900 nm spectral range with the maximum values of two-photon action cross section for ligand/metal complex ∼(90-130) GM, using a standard two-photon induced fluorescence methodology under femtosecond excitation. The nature of the 2PA bands was analyzed by quantum chemical methods and a specific dependence on metal ion binding processes was shown. Ratiometric fluorescence detection (420/650 nm) provided a good dynamic range (10-4 to 10-6 M) for detecting Zn 2+, which along with the good photostability and 2PA properties of probe 1 makes it a good candidate in two-photon fluorescence microscopy imaging and sensing of Zn ions. © 2010 American Chemical Society

Solvent Effect On The Steady-State Fluorescence Anisotropy Of Two-Photon Absorbing Fluorene Derivatives

The effect of solvent polarity on the fluorescence properties of several two-photon absorbing fluorene derivatives was investigated. A strong solvatochromic effect was observed for symmetrical fluorene compound, which can be explained by large changes in the quadrupolar moment under excitation. Limiting values of excitation anisotropy of the investigated fluorenes exhibited a dependence on solvent polarity, and the angles between the absorption and emission transition dipole moments decrease in polar solvents by more than a factor of two. © 2006 Elsevier B.V. All rights reserved

Aggregate Formation of Boron-Containing Molecules in Thermal Vacuum Deposited Films

The spectral properties of new boron-containing dyes were studied. One-component (pure dyes) and composite “Alq3+dye” thin films were fabricated using the thermal vacuum deposition method. The positions of the transmission spectra maxima in a one-component film are different for different film thicknesses. The best correlation of the maxima positions of the dye transmission spectra in solid and liquid solutions was observed for thicknesses of films close to a few (up to 10) monolayers. On the other hand, the absorption spectra maxima positions of one-component dye films (upper 10 nm) and composite films with high concentration, did not match the corresponding positions of absorption spectra maxima recorded in solutions. Comparison of the absorption spectra in one-component dye films and in solutions indicates the presence of both monomers and their aggregates in one-component films (contrary to solutions where such processes of aggregation do not take place, even at very high concentrations). Simultaneously with aggregation manifestation in the absorption spectra, the intensity of fluorescence of one-component dye films dramatically decreases. A quantum chemical simulation of the possible relative arrangement of two dye molecules indicates that the most possible of the simplest types of aggregates are physical dimers. Films of practical importance (due to efficient energy transfer from host to guest molecules when all singlet excitons are captured) possess a high quantum yield of fluorescence when reaching an impurity concentration of a few percent (aggregation does not take place yet)

Self-Assembly for Two Types of J-Aggregates: Cis-Isomers of Dye on the Carbon Nanotube Surface and Free Aggregates of Dye Trans-Isomers

Development of novel nanoscale devices requires unique functional nanomaterials. Furthermore, chemical design of different nanoparticles in one unit is a complex task, particularly the application of self-assembly J-aggregates, which can substantially advance the nanomaterial's properties due to resonant delocalization of excitons. Here, we have demonstrated for the first time formation of resonantly coherent J-aggregates on carbon nanotubes with highly efficient energy transfer from the aggregates to the nanotubes. All the energy of photons absorbed by the aggregates is conveyed to the nanotubes, completely quenching the J-band emission and photosensitizing the nanotubes. Overall, we discovered formation of two types of J-aggregates, where one type is related to self-assembly of cis-isomers on the nanotube surface and the second type is associated to self-organizing trans-isomers into free J-aggregates without the nanotubes. Importantly, the J-aggregates on carbon nanotubes with strong energy transfer peaks of photoluminescence in the near infrared range are of high interest for practical applications on biomedical imaging and nanoscale optoelectronic and nanophotonic devices