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

A dioxaborine cyanine dye as a photoluminescence probe for sensing carbon nanotubes

The unique properties of carbon nanotubes have made them the material of choice for many current and future industrial applications. As a consequence of the increasing development of nanotechnology, carbon nanotubes show potential threat to health and environment. Therefore, development of efficient method for detection of carbon nanotubes is required. In this work, we have studied the interaction of indopentamethinedioxaborine dye (DOB-719) and single-walled carbon nanotubes (SWNTs) using absorption and photoluminescence (PL) spectroscopy. In the mixture of the dye and the SWNTs we have revealed new optical features in the spectral range of the intrinsic excitation of the dye due to resonance energy transfer from DOB-719 to SWNTs. Specifically, we have observed an emergence of new PL peaks at the excitation wavelength of 735 nm and a redshift of the intrinsic PL peaks of SWNT emission (up to 40 nm) in the near-infrared range. The possible mechanism of the interaction between DOB-719 and SWNTs has been proposed. Thus, it can be concluded that DOB-719 dye has promising applications for designing efficient and tailorable optical probes for the detection of SWNTs

Mixing of Excitons in Nanostructures Based on a Perylene Dye with CdTe Quantum Dots

Semiconductor quantum dots of the A2B6 group and organic semiconductors have been widely studied and applied in optoelectronics. This study aims to combine CdTe quantum dots and perylene-based dye molecules into advanced nanostructure system targeting to improve their functional properties. In such systems, new electronic states, a mixture of Wannier–Mott excitons with charge-transfer excitons, have appeared at the interface of CdTe quantum dots and the perylene dye. The nature of such new states has been analyzed by absorption and photoluminescence spectroscopy with picosecond time resolution. Furthermore, aggregation of perylene dye on the CdTe has been elucidated, and contribution of Förster resonant energy transfer has been observed between aggregated forms of the dye and CdTe quantum dots in the hybrid CdTe-perylene nanostructures. The studied nanostructures have strongly quenched emission of quantum dots enabling potential application of such systems in dissociative sensing

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

Effect of the charge state on the photoluminescence spectra of melanin

Steady-state and time-resolved photoluminescence (PL) spectra of natural and synthetic melanin, as well as melanin composites with surfactant, sodium dodecylbenzenesulfonate, and polymethine dye, astraphloxin, have been studied. The melanin molecules having differently charged peripheral groups with terminal O atoms and OH groups mixed with the negatively charged surfactant or positively charged astraphloxin dye feature new PL spectral bands. The kinetics of PL and time-resolved emission spectra for the melanin and the composites were also investigated and discussed in terms of intermolecular complexation, nano-aggregation and formation of chargetransfer states. The studies are aiming to understand the electronic properties of various melanins, particularly natural ones

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