Absorption-spectral features of single-walled carbon nanotubes

Quantum mechanism of light energy propagation through an avian retina

Taking into account the ultrastructure of the Pied Flycatcher foveal retina reported earlier and the earlier reported properties of Müller cell (MC) intermediate filaments (IFs) isolated from vertebrate retina, we proposed a quantum mechanism (QM) of light energy transfer from the inner limiting membrane level to visual pigments in the photoreceptor cells. This mechanism involves electronic excitation energy transfer in a donor-acceptor system, with the IFs excited by photons acting as energy donors, and visual pigments in the photoreceptor cells acting as energy acceptors. It was shown earlier that IFs with diameter 10 nm and length 117 μm isolated from vertebrate eye retina demonstrate properties of light energy guide, where exciton propagates along such IFs from MC endfeet area to photoreceptor cell area. The energy is mostly transferred via the contact exchange quantum mechanism. Our estimates demonstrate that energy transfer efficiencies in such systems may exceed 80-90%. Thus, the presently developed quantum mechanism of light energy transfer in the inverted retina complements the generally accepted classic optical mechanism and the mechanism whereby Müller cells transmit light like optical fibers. The proposed QM of light energy transfer in the inverted retina explains the high image contrast achieved in photopic conditions by an avian eye, being probably also active in other vertebrates.

Estimation of the (n,m) Concentration Distribution of Single-Walled Carbon Nanotubes from Photoabsorption Spectra

Deconvolution of the absorption spectrum of single-walled carbon nanotubes (SWNTs) into distinct (n,m) contributions is complicated because transition energies are closely spaced. The algorithm presented in this work attempts to simplify the problem by grouping nanotubes with similar transition energies and assigning weights to their spectral contributions. Voigt line shapes were used to fit absorption spectra of sodium dodecyl sulfate suspended HiPco SWNT and CoMoCat SWNT. Line widths for the metallic (93.42 meV) and two semiconducting regions (57.96 and 29.86 meV) were obtained from the absorption spectra of DNA-wrapped SWNT fractionated by ion-exchange chromatography. The method is used to describe the reaction kinetics of certain HiPco SWNTs upon reaction with 4-chlorobenzene diazonium and 4-hydroxybenzene diazonium salts. The code for deconvolution has been provided as open source in the Supporting Information for future modifications.

Strain-induced interference effects on the resonance Raman cross section of carbon nanotubes

In this Letter, we report the effects of strain on the electronic properties of single-wall carbon nanotubes. When we normalize the electronic transition energies to the corresponding values obtained for unstrained tubes, we obtain that, regardless of the tube diameter, all the data collapse onto universal curves following an n - m = constant family pattern. In the case of metallic tubes, quantum interference effects on the Raman cross section are predicted for strained tubes when the energies of the lower and the upper components have nearly the same values. Experimental evidence for the strain-induced Raman cross section changes is observed in single nanotube spectroscopy.