Bis-porphyrin Racks with space-separated co-planar porphyrin rings

Abstrac

Photoinduced electron transfer in a non-covalently linked donor-acceptor system: a bis-porphyrinic host and a naphthalene diimide guest

Abstrac

Porphyrin-containing molecular capsules : metal mediated dimerization of a bis-porphyrin cavity

Molecular systems that can enclose space in a controlled fashion are receiving active attention in the current literature.2 Noncovalent interactions and self-assembly protocols are emerging as alternatives superior to assemblies largely prepared by covalent synthesis. In particular, capsule systems that reversibly form have been predominantly based on hydrogen bonds. These include Rebeks' "sportsballs" which stem from the glycoluril building block; urea-functionalizedcalixarene dimers reported independently by Rebek, Bohmer, Reinhouldt and de Mendoza;2 and giant sperical arrays constructed from calizarene units.3 Metal ion coordination has also been explored as a means of host assembly and has been reviewed.

Bisporphyrin cavities : from guest complexation to molecular capsule formation

Bisporphyrin cavities : from guest complexation to molecular capsule formatio

A building BLOCK approach to bis-porphyrin cavity systems with convergent and divergent wall orientations

Porphyrin containing molecular building blocks have been linked together using s-tetazine or 1,3-dipolar coupling protocols to yield bis-porphyrin cavities of defined shape and size which were evaluated by molecular modelling

Position-addressable nano-scaffolds. II. The introduction of one, two, or three addressable succinimide linkage points onto the under-surface of 'southern' cavity bis-porphyins

Cavity bis-porphyins containing up to three addressable succinimide rings on the underface are reported for the first time. This is achieved by site-selective addition of o-chloranil to the 7-oxanorbornene TT-bond of O-bridged sesquinorbornadienosuccinimide (1a) to form a scaffold a-dione, followed by condensation with porphyrindiamine (12) to produce a porphyrin-containing norbornene BLACK (13) incorporated a succinimide ring fused to the underside. Dual 1,3-dipolar coupling of (13) with alicyclic bis-epoxides (15) formed the cavity bis-porphyrins (16) containing two succinimide rings while similar 1,3-dipolar coupling with succinimide-containing bis-epoxide (17) gave the extended cavity bis-porphyrin (18) having three succinimide rings within the cavity section a similar cycloaddition/condensation strategy provides the shortest route to cavity bis-porphyrins containina a single succinimide ring yet reported

Bis-porphyrin clamp for photo- and electroactive guests for light energy conversion: a spectroscopic and photophysical study

 The spectroscopic and photophysical characterization of a V-shaped Zn(II) bis-porphyrinic structure, ZnH, its free-base analogue FBH and the model porphyrin components ZnB and FBB is presented. With respect to the unsubstituted zinc porphyrin Zn, asymmetric substitution with tetraazaanthracene is responsible for the increase of dipole moment in the excited state of Zn(II) derivatives. The charge transfer character of the transition causes a remarkable solvent effect on the luminescence properties. Axial complexation of the zinc ion in ZnB and ZnH by pyridine induces a strong perturbation of the photophysical properties. In the free base derivatives FBB and FBH the substituent displaces the equilibrium population with respect to unsubstituted FB, on both the ground and excited states of the two tautomers, allowing for the presence of two independent populations (ca. 90% and 10%) of distinct species detected by UV-Vis spectroscopy. The data are supported by semiempirical calculations. </p

Photoinduced electron transfer in bisporphyin-diimide complexes

The bisporphyrin host ZnH was synthesized, and its complexation with two aromatic diimide guest molecules, bis(pyridyl)naphthalenediimide NIN and bis(pyridyl)phenyldiimide PIN, was investigated by 1H NMRand UV/Vis spectroscopy. The diimide guests were complexed simultaneously with both metalloporphyrins of the host, with association constants on the order of 10 8 M-1. The processes occurring in the complex after excitation of the porphyrinic host were studied by steady-state and time-resolved emission and transient absorption spectroscopy. Complexation alters the photophysical properties of the host ZnH; the luminescence bands shift to the red by 30 nm in the complexed forms, while the emission quantum yield and the lifetime decrease. Comparison of a complex between ZnH and a model guest unable to undergo photoinduced processes allowed us to establish that, in the diimide complexes, quenching of the porphyrinic luminescence occurs with a rate of 1.1x10 10 s-1. The process is identified as an electron transfer from the excited singlet of the porphyrinic host to the imide guest, which yields charge-separated states with a lifetime of 710 ps for ZnH+-NIN- and 260 ps for ZnH+-PIN-

Binary image classification: A genetic programming approach to the problem of limited training instances

© 2016 by the Massachusetts Institute of Technology. In the computer vision and pattern recognition fields, image classification represents an important yet difficult task. It is a challenge to build effective computer models to replicate the remarkable ability of the human visual system, which relies on only one or a few instances to learn a completely new class or an object of a class. Recently we proposed two genetic programming (GP) methods, one-shot GP and compound-GP, that aim to evolve a program for the task of binary classification in images. The two methods are designed to use only one or a few instances per class to evolve the model. In this study, we investigate these two methods in terms of performance, robustness, and complexity of the evolved programs. We use ten data sets that vary in difficulty to evaluate these two methods. We also compare them with two other GP and six non-GP methods. The results show that one-shot GP and compound-GP outperform or achieve results comparable to competitor methods. Moreover, the features extracted by these two methods improve the performance of other classifiers with handcrafted features and those extracted by a recently developed GP-based method in most cases

A One-shot Learning Approach to Image Classification using Genetic Programming

In machine learning, it is common to require a large number of instances to train a model for classification. In many cases, it is hard or expensive to acquire a large number of instances. In this paper, we propose a novel genetic programming (GP) based method to the problem of automatic image classification via adopting a one-shot learning approach. The proposed method relies on the combination of GP and Local Binary Patterns (LBP) techniques to detect a predefined number of informative regions that aim at maximising the between-class scatter and minimising the within-class scatter. Moreover, the proposed method uses only two instances of each class to evolve a classifier. To test the effectiveness of the proposed method, four different texture data sets are used and the performance is compared against two other GP-based methods namely Conventional GP and Two-tier GP. The experiments revealed that the proposed method outperforms these two methods on all the data sets. Moreover, a better performance has been achieved by Naïve Bayes, Support Vector Machine, and Decision Trees (J48) methods when extracted features by the proposed method have been used compared to the use of domain-specific and Two-tier GP extracted features. © Springer International Publishing 2013