In quest of a systematic framework for unifying and defining nanoscience

This article proposes a systematic framework for unifying and defining nanoscience based on historic first principles and step logic that led to a “central paradigm” (i.e., unifying framework) for traditional elemental/small-molecule chemistry. As such, a Nanomaterials classification roadmap is proposed, which divides all nanomatter into Category I: discrete, well-defined and Category II: statistical, undefined nanoparticles. We consider only Category I, well-defined nanoparticles which are >90% monodisperse as a function of Critical Nanoscale Design Parameters (CNDPs) defined according to: (a) size, (b) shape, (c) surface chemistry, (d) flexibility, and (e) elemental composition. Classified as either hard (H) (i.e., inorganic-based) or soft (S) (i.e., organic-based) categories, these nanoparticles were found to manifest pervasive atom mimicry features that included: (1) a dominance of zero-dimensional (0D) core–shell nanoarchitectures, (2) the ability to self-assemble or chemically bond as discrete, quantized nanounits, and (3) exhibited well-defined nanoscale valencies and stoichiometries reminiscent of atom-based elements. These discrete nanoparticle categories are referred to as hard or soft particle nanoelements. Many examples describing chemical bonding/assembly of these nanoelements have been reported in the literature. We refer to these hard:hard (H-n:H-n), soft:soft (S-n:S-n), or hard:soft (H-n:S-n) nanoelement combinations as nanocompounds. Due to their quantized features, many nanoelement and nanocompound categories are reported to exhibit well-defined nanoperiodic property patterns. These periodic property patterns are dependent on their quantized nanofeatures (CNDPs) and dramatically influence intrinsic physicochemical properties (i.e., melting points, reactivity/self-assembly, sterics, and nanoencapsulation), as well as important functional/performance properties (i.e., magnetic, photonic, electronic, and toxicologic properties). We propose this perspective as a modest first step toward more clearly defining synthetic nanochemistry as well as providing a systematic framework for unifying nanoscience. With further progress, one should anticipate the evolution of future nanoperiodic table(s) suitable for predicting important risk/benefit boundaries in the field of nanoscience

The violent youth of bright and massive cluster galaxies and their maturation over 7 billion years

In this study, we investigate the formation and evolution mechanisms of the brightest cluster galaxies (BCGs) over cosmic time. At high redshift (z ∼ 0.9), we selected BCGs and most massive cluster galaxies (MMCGs) from the Cl1604 supercluster and compared them to low-redshift (z ∼ 0.1) counterparts drawn from the MCXC meta-catalogue, supplemented by Sloan Digital Sky Survey imaging and spectroscopy. We observed striking differences in the morphological, colour, spectral, and stellar mass properties of the BCGs/MMCGs in the two samples. High-redshift BCGs/MMCGs were, in many cases, star-forming, late-type galaxies, with blue broad-band colours, properties largely absent amongst the low-redshift BCGs/MMCGs. The stellar mass of BCGs was found to increase by an average factor of 2.51 ± 0.71 from z ∼ 0.9 to z ∼ 0.1. Through this and other comparisons, we conclude that a combination of major merging (mainly wet or mixed) and in situ star formation are the main mechanisms which build stellar mass in BCGs/MMCGs. The stellar mass growth of the BCGs/MMCGs also appears to grow in lockstep with both the stellar baryonic and total mass of the cluster. Additionally, BCGs/MMCGs were found to grow in size, on average, a factor of ∼3, while their average Sérsic index increased by ∼0.45 from z ∼ 0.9 to z ∼ 0.1, also supporting a scenario involving major merging, though some adiabatic expansion is required. These observational results are compared to both models and simulations to further explore the implications on processes which shape and evolve BCGs/MMCGs over the past ∼7 Gyr

Reaction of aromatic amines with Cu(ClO<SUB>4</SUB>)<SUB>2</SUB> in acetonitrile as a facile route to amine radical cation generation

This Letter describes a very simple and effective method for the generation and study of radical cations of aromatic amines. It is shown that simple mixing of micro molar solutions of aromatic amines with micro molar amounts of Cu(ClO<SUB>4</SUB>)<SUB>2</SUB> in acetonitrile solution leads to formation of amine radical cations in good yields. The radical cations thus generated are unequivocally characterized by their absorption and electron spin resonance spectra. It is proposed that the radical cations are formed through the donation of an electron from the amines to Cu<SUP>2+</SUP>

Photoinduced electron transfer in hydrogen bonded donor-acceptor systems. Study of the dependence of rate on free energy and simultaneous observation of the Marcus and Rehm-Weller behaviors

Hydrogen bonding networks play a very important role in biological electron-transfer processes. The free energy dependence of electron transfer in a few small-molecule donor-acceptor systems, having hydrogen bonding appendages, were studied by fluorescence lifetime quenching measurements. Two types of electron transfers take place in these systems. A fraction of the molecules associates and exists as hydrogen bonded species and electron transfer in this segment is unimolecular. A major fraction of the donors and acceptors freely diffuse in the medium and electron transfer is bimolecular in this segment. Free energy dependence studies showed that the former obeys the Marcus equation and the latter follows the Rehm-Weller behavior. The absence of the inverted region in bimolecular charge separation reactions is thus attributed to diffusion in the moderately large driving force regime

Photophysical and electron-transfer properties of a few 2,6-dimethyl-4-arylpyrylium derivatives

Photophysical and electron transfer properties of pyrylium salts 1-4 were investigated. The photophysical properties include absorption and fluorescence spectra, quantum yields, fluorescence lifetimes and phosphorescence spectra. Laser flash photolysis of 1-4 in degassed dichloromethane led to the formation of transients assigned to the triplets of these molecules. The quantum yields of triplet formation and the extinction coefficients of the triplet-triplet absorption were determined. Electron transfers to the excited states of 1-4 from biphenyl were studied by fluorescence quenching and laser flash photolysis. The intermediate radical ions formed in the electron transfer reactions were characterized. In the case of 1-3, only the singlet excited states were involved in electron transfer reactions, whereas, in the case of 4, the singlet as well as the triplet excited states act as electron acceptors. Involvement of the triplet in the electron transfer reactions, led to higher Φion and lower kbet values in the case of 4. Thus, suitable modification of the structure of pyrylium salts can lead to molecules with very good photoelectron transfer properties

Structure-photophysics correlation in a series of 2,6-dimethyl-4-arylpyrylium derivatives

Photophysical properties of a group of closely related pyrylium cations, 1-5, are reported. Our results indicate that these cations have two excited states with similar energies and that the substituent determines which of these has the lowest energy. For cations 1 and 2, the lowest excited state has Tict character. In the case of 3-5, the photophysical properties are better explained by invoking a planar excited state

Photoinduced charge transfer processes in ultrasmall semiconductor clusters. Photophysical properties of CdS clusters in nafion membrane

The photophysical properties of quantized CdS clusters in a perfluorosulfonate polymer (Nafion) film have been investigated by time-resolved emission spectroscopy. The ultrasmall CdS clusters were prepared by exposing Cd2+-exchanged polymer film to H2S. size-dependent absorption and emission properties were observed during the growth of these clusters. The emission decay is multiexponential with lifetimes ranging from 0·85 to 480 ns

Synthesis and photophysical studies of donor-acceptor substituted tetrahydropyrenes

The tetrahydropyrene derivatives 2-N,N-dimethylamino-7-nitro-4,5,9,10-tetrahydropyrene (1) and 2-N,N-dimethylamino-7-acetyl-4,5,9,10-tetrahydropyrene (2) were synthesized and characterized. Photophysical properties of these molecules were investigated in several solvents. The absorption spectrum of 1 shows a slight red shift with solvent polarity, whereas that of 2 remains more or less unchanged. Fluorescence spectra of these compounds exhibit large, solvent-polarity-dependent Stokes shifts. The Stokes shifts are correlated to E<SUB>T</SUB>(30) and E<SUP>N</SUP><SUB>T</SUB> parameters and were quantitatively analyzed by the Mataga-Liptay equation. Both compounds show low fluorescence quantum yields in cyclohexane. Nanosecond flash photolysis studies suggested that the low quantum yield in cyclohexane is due to intersystem crossing to a triplet state. In the case of 2, the fluorescence quantum yields are high in all other solvents. In the case of 1 fluorescence quantum yields are very low in polar solvents and this is explained by invoking a twisted intramolecular charge transfer state