No abstract

Core/shell quantum dots (QDs) are of high scientific and technological importance as these nanomaterials have found a number of valuable applications. In this paper, we have investigated the dependence of optical activity and photoluminescence upon CdS shell thickness in a range of core-shell structured CdSe/CdS QDs capped with chiral ligands. For our study, five samples of CdSe/CdS were synthesized utilizing successive ion layer adsorption and reaction to vary the thickness of the CdS shell from 0.5 to 2 nm, upon a 2.8 nm diameter CdSe core. Following this, a ligand exchange of the original aliphatic ligands with l- and d-cysteine was carried out, inducing a chiroptical response in these nanostructures. The samples were then characterized using circular dichroism, photoluminescent spectroscopy, and fluorescence lifetime spectroscopy. It has been found that the induced chiroptical response was inversely proportional to the CdS shell thickness and showed a distinct evolution in signal, whereas the photoluminescence of our samples showed a direct relationship to shell thickness. In addition, a detailed study of the influence of annealing time on the optical activity and photoluminescence quantum yield was performed. From our work, we have been able to clearly illustrate the approach and strategies that must be used when designing optimal photoluminescent optically active CdSe/CdS core-shell QDs.

Considerable progress has been made in recent years in the search for synthetic methods leading to functionalized porphyrins, especially for modification of either the β‐ or meso positions. For the latter, total synthesis based on condensation methods or partial synthesis through functionalization of preformed porphyrin have emerged as possible methods. The increasing number of possible technical and medicinal applications for unsymmetrically meso‐substituted porphyrins requires straightforward methods for the preparation of the so‐called ABCD‐porphyrins, i.e., porphyrins with up to four different meso substituents. Here, we describe new strategies for the synthesis of ABCD‐type porphyrins based on porphyrin reactions with organolithium reagents and the use of Pd‐catalyzed coupling reactions. With the whole repertoire of contemporary functionalization methods, a comprehensive analysis and comparison of the various strategies for A‐, AB‐, A2B‐, ABC‐, A2BC‐ and ABCD‐type porphyrins is given. In addition, we report on the synthesis of new functionalized derivatives for some of these porphyrin classes. In practical terms and taking an applied‐science‐oriented approach, the synthesis of unsymmetrically meso‐substituted porphyrins is best accomplished by a combination of well‐developed condensation methods with subsequent functionalization by organolithium compounds or transition‐metal‐catalyzed coupling protocols. The methods described are suitable for the preparation of porphyrins for many divergent applications ranging over amphiphilic porphyrins for photodynamic therapy, push‐pull systems for optical applications and chiral systems useful in catalysis to donor–acceptor systems suitable for electron‐transfer studies.

nickel(II) porphyrins in dichloromethane is reported to comprehensively access their sterically induced distortions from planarity. Thus, the tutorial review focuses on both resonance Raman spectroscopic investigations and structural investigations based on DFT. We relate different theoretical and experimental methodologies to predict out-of-plane distortions of the porphyrin macrocycles which are quantified by normal-coordinate structural decomposition. This comprehensive compilation reveals shortcomings in the molecular mechanic calculations and illustrates the impact of crystal packing forces on crystal structures. Non-planar distortions shift the experimentally observed resonance Raman marker bands v 2 , v 3 and v 4 to lower frequency. A revised correlation between this shift and the calculated structural parameter (ruffling angle) is presented and reveals deviations from reported correlations based on molecular mechanics.

Current applications of porphyrins in medicine and optics, such as photodynamic therapy or nonlinear absorbers, increasingly require the use of far-red absorbing dyes. Modifications of the porphyrin structure to accommodate these conditions can be achieved by extending the conjugation of the porphyrin π-system, which causes a bathochromic shift in the absorption spectrum. Thus, conjugated porphyrin oligomers have found widespread use. However, past synthetic strategies have mainly targeted symmetric porphyrin dimers, trimers, and oligomers, which limit the practical use of such chromophores. Here, a series of symmetric and unsymmetric dimeric and trimeric porphyrin systems, which are connected by conjugated linkers, namely alkyne and phenylacetylene, were synthesized by palladium-catalyzed C-C coupling re-

As the world strives to create a more sustainable environment, green chemistry has come to the fore in attempts to minimize the use of hazardous materials and shift the focus towards renewable sources. Chlorophylls, being the definitive "green" chemical are rarely used for such purposes and this article focuses on the exploitation of this natural resource, the current applications of chlorophylls and their derivatives whilst also providing a perspective on the commercial potential of large-scale isolation of these pigments from biomass for energy and medicinal applications.

We report the synthesis and characterization of a meso-meso directly linked bisporphyrin 6 bearing both alkyl and aryl residues. Oxidative fusing results in a mesomeso,β−β,β−β-linked bisporphyrin. The first crystal structure analysis of a meso-meso directly linked porphyrin dimer 6 shows the inequivalency of the two porphyrin units with regard to the macrocycle conformation. Quite distinct mixings of distortion modes were observed for the two aromatic macrocycles.

Current applications of porphyrins in medicine and optics, such as photodynamic therapy or nonlinear absorption, increasingly require the use of far-red absorbing dyes. Modifications to the porphyrin structure to accommodate these conditions can be achieved by extending the conjugation of the porphyrin π-system, which will cause a bathochromic shift in the absorption spectrum. Thus, conjugated porphyrin oligomers have found widespread use. However, past synthetic strategies have mainly targeted symmetric porphyrin dimers, trimers, and oligomers which limit the practical use of such chromophores. To further extend the absorption profile, a series of symmetric and unsymmetric dimeric and oligomeric porphyrin β-β, meso-meso, β'-β' triply-fused systems were synthesised via oxidative coupling methods. This required an analysis and optimization of the various synthetic strategies. These arrays exhibit a dramatic bathochromic shift into the nearinfrared region, many displaying absorption of greater than 1050 nm. Additionally, post-fusing chemical transformations, namely organolithium, cycloaddition and transition-metal catalysed reactions, at the meso-and β-positions enables the fine-tuning of such arrays with the aim of enhancing the bathochromic shift and their potential optical applications. IntroductionLong wavelength absorption of porphyrins is desired for a wide range of applications [1] and there are many means to achieve such a characteristic. These include: the synthesis of porphyrin arrays connected via conjugated linkers, [2] the construction of perturbed porphyrinoid macrocycles via various cycloaddition reactions [3] and the construction of fused or directly linked porphyrin arrays. [4] The latter is favorable as triply linked porphyrin arrays result in the extension of the absorption profile into the near-IR region. Pioneering methods developed by Sugiura et al. [5] and Osuka and co-workers [6] can be adopted for the generation of so-called triply fused porphyrin dimers and higher arrays. [4a,7] By doing so, a λ max of 1050 nm and beyond may be achieved and these covalently linked multiporphyrin arrays can act as multichromophoric model systems for the study of electron transfer in light-harvesting systems. Although the Osuka group, amongst others, [4b,8] have extensively researched this area, their work primarily deals with symmetric arrays and photophysical studies of such porphyrins. [9] Only limited research has been carried out on so-called unsymmetrical fused dimers [10] and postmodifications of fused arrays. [11] We envisaged developing both novel symmetric fused dimers and unsymmetric arrays, for the purpose of applying them to fields of research such as NLO, [12] OLEDs [13] and two-photon absorption PDT (2PA-PDT). [14] By the introduction of various substituents to the porphyrin periphery [15] and subsequent post-fusing modifications, the arrays can be finetuned for PDT, via the introduction of water solubilizing groups, [14a, 16] and NLO via the introduction of donor/acceptor groups to...