Dendritic Architectures for Design of Photo– and Spin–Functional Nanomaterials

Abstract

ABSTRACT:Unlike ordinary linear polymers, dendritic architecture is unique in the terms of its elaborative capability for total control over molecular design parameters at the single molecular level, i.e., molecular size, branching pattern, structure, and morphology, thereby provides a new platform for the creation of functional materials with nanometer-scale precision. This review mainly concerns recent works on the development of dendritic nanomaterials with a focus on photo-and spin-related functionalities. Strategy for the incorporation of chromophores to build up light-harvesting antennae is presented with an emphasis on morphology and size effects. Dendritic macromolecules for photoinduced electron transfer are categorized based on chromophores that serve as the active center to absorb light and trigger photochemical process. In this context, dendrimers bearing porphyrin, conjugated polymer, and fullerene for realization of long-lived charge-separation state and light energy conversion are highlighted. On the other hand, design of dendritic macromolecules for spin-functional materials is focused on dendronized organic radicals and dendritic coordination polymers. Especially, spin-functional soft materials with an aim for spin manipulation and novel magneticoptical switches are emphasized. [doi:10.1295/polymj.PJ2007006] KEY WORDS Dendrimer / Light Harvesting / Photoinduced Energy Transfer / Photoinduced Electron Transfer / Magnetic Soft Materials / Spin Transition / Radicals / Dendritic architecture, characterized by its iteratively branched structure, is one of the most pervasive topology, which can be easily found at a variety of dimensional scales such as in abiotic phenomena including snow crystals and lightning patterns, and in biological systems, for example, tree branches and neuron networks. From a synthetic point of view, such architecture will enable chemists to construct molecules with their components linked in a radial fashion, which is hardly achieved via ordinary synthetic methodology. With the development of two main strategies, i.e. divergent and convergent approaches, 1-3 innumerable dendritic structures have been reported up to date. 'Dendrimer' termed by Tomalia in 1985 has been recognized as the fourth major class of macromolecular architectures. Benefiting from the well-established synthetic strategies, chemists are now able to precisely control the size and shape of the dendrimer frameworks as well as the numbers and positions of the functional groups. This molecular design flexibility is one of the most unique characters, which distinguished dendrimers from all other linear, hyperbranched, and star-shaped macromolecules.On the other hand, the myriad of sophisticated natural processes such as light harvesting, energy transduction and conversion stimulated chemists in the design of various functional molecules and their assemblies, which lead to many significant scientific and technological advances over the past decades. In relation to this, dendritic architecture, due to its well-def...

Environment-Assisted Quantum Transport

“…Binary trees appear in a wide variety of situations, ranging from computer science [43] to quantum physics and quantum information science [13]. Specifically, they arise in classical and quantum random walks [13] and certain molecular structures such as dendrimers [44]. The effect of static disorder of the site energies in quantum walks on binary trees has been studied in Refs.…”

Mixed spin-1/2 and spin-1 Ising model with uniaxial and biaxial single-ion anisotropy on the Bethe lattice

“…In particular, the mixed-spin Ising models defined on the Bethe lattice can be useful in providing a deeper insight into the magnetism of dendrimeric organic molecules containing radicals as their magnetic sites [54][55][56][57][58][59]. In this respect, the lattice-statistical models with spin-1/2 and spin-1 sites are the most useful ones because the most common dendrimeric organic magnets are based on radicals, such as carbenes, polyethers, trityl and trityl-anionic radicals, perchlorotriphenylmethyl radical, etc., whose basic building blocks are either spin-1/2 or spin-1 sites.…”

Mixed spin-1/2 and spin-1 Ising model with uniaxial and biaxial single-ion anisotropy on Bethe lattice

“…Furthermore, it should be stressed that the present results are interesting both from the academic point of view (because of their exactness) as well as from the experimental viewpoint. Namely, the mixed-spin Ising models defined on the Bethe lattices can be useful in providing a deeper insight into a magnetism of dendrimeric organic molecules containing radicals as their magnetic sites [34][35][36][37][38][39]. In this respect, the lattice-statistical models with spin-1/2 and spin-1 sites are the most useful ones as the most common dendrimeric organic magnets are based on radicals such as carbenes, polyethers, trityl and trityl-anionic radicals, perchlorotriphenylmethyl radical and so on, which are basic building blocks of either the spin-1/2 or spin-1 sites.…”