Chemistry in the 21st century: Looking into the future

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  • 122

    ISSN 1019-3316, Herald of the Russian Academy of Sciences, 2009, Vol. 79, No. 2, pp. 122129. Pleiades Publishing, Ltd., 2009.Original Russian Text V.A. Tartakovskii, S.M. Aldoshin, 2009, published in Vestnik Rossiiskoi Akademii Nauk, 2009, Vol. 79, No. 3, pp. 229237.

    Our paper is based on predictive analysis of chemis-try development in the 21st century and was preparedjointly with Academicians A.L. Buchachenko,V.I. Minkin, A.I. Konovalov, I.I. Moiseev, andYu.D. Tretyakov and with the participation of Acade-micians A.R. Khokhlov, A.G. Merzhanov, R.Z. Sag-deev, and G.A. Abakumov and RAS CorrespondingMembers G.B. Manelis, S.D. Varfolomeev, andV.I. Ovcharenko. In fact, our paper is a collective workof the RAS Branch of Chemistry and Materials Sci-ences. We will discuss prospects for the development ofchemistry in this century.

    All substances obtained by chemists are the result ofunorganized chemical reactions, in which atoms andmolecules meet at random in time and space. At thesame time, chemistry in nature builds all its objectsrelying on the high organization of the molecular andsupramolecular structure. The awareness of this factand the orientation of chemistry toward molecular andsupramolecular organization is a strategic trend in thedevelopment of chemistry in the 21st century. There-fore, let us begin with

    supramolecular chemistry.

    Thisscience appeared in Russia about 30 years ago andstarted to develop in Moscow, Novosibirsk, Kazan, andother cities. At present, it has achieved brilliant suc-cesses mainly thanks to the findings of the scientificschools of Academicians Konovalov, M.V. Alfimov,and A.Yu. Tsivadze and some other research centers.

    It is obvious today that supramolecular systemshave a special niche or level in the hierarchy of matter.The atomic level is followed by the molecular one withthe covalent form of binding between atoms. Thencomes the supramolecular level with noncovalent(intermolecular) binding. Supramolecular systemsemploy organizational and functioning principles ofmatter, such as molecular recognition, selective bind-ing, receptorsubstrate interaction, transmembranetransport, and supramolecular catalysis. Molecular rec-ognition (which is chemical informatics) serves as thebasis for the self-organization and programmable self-assembly of supramolecular systems, which were uti-lized to the maximum during the formation of biologi-cal objects. The key structures of biological systems,

    for example, the double helices of nucleic acids, cellmembranes, and enzymes, are supramolecular systems.

    Proceeding from the above principles of organiza-tion and function of supramolecular systems and theirvery close structural and functional relation to biologi-cal objects, we predict two crucial and basic ways ofdevelopment of supramolecular chemistry in the21st century. First is the development of methods ofsupramolecular chemistry as an instrument of con-structing nanoparticles and nanomaterials with presetproperties and the use of the programmable self-assem-bly of supramolecular systems. Second is the creationof artificial systems (including natural analogs) capableof interaction with biological objects at the supramo-lecular level (Fig. 1).

    Chemistry has reached the topmost horizon: theability to detect, spatially fix, transfer, and recognize asingle molecule and measure almost all its materialproperties. This topmost horizon creates the elementbase and develops technologies to manipulate singlemolecules for nanooptics, nanomechanics, and nano-electronics. This is a prologue to a new technologicalcivilization,

    molecular electronics

    , which operates onmillivolts and nanoamperes.

    Developed countries already have dozens of labora-tories duly equipped, and billions of dollars are allo-cated to finance them. The scientific world is in a race,being clearly aware that the position of any country inthe hierarchy of developed countries depends on break-throughs in this sphere.

    Molecular electronics and spintronics are the mostrapidly developing spheres of nanotechnology, whoseorigin and development sociologists view as the fifthindustrial revolution. Let us briefly overview the devel-opment of this field of chemistry. Assumptions thatmolecules can conduct electric current were made backin the early 1950s by R.S. Mulliken and A. Szent-Gyr-gyi, but usually the origin of molecular electronics isassociated with the 1974 publication of A. Aviram andM. Ratner. They proposed the idea of a molecular rec-tifier (diode): a molecule containing powerful

    -donorand

    -acceptor groups, divided by a

    -spacer, andplaced between the electrodes. Such molecules modelthe

    pn

    junction in semiconductors (Fig. 2).

    DOI:

    10.1134/S1019331609020075

    Chemistry in the 21st Century: Looking into the Future

    Paper by Academicians V. A. Tartakovskii and S. M. Aldoshin

    Scientific Session of the General Meetingof the Russian Academy of Sciences

  • HERALD OF THE RUSSIAN ACADEMY OF SCIENCES

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    CHEMISTRY IN THE 21st CENTURY: LOOKING INTO THE FUTURE 123

    The next stage is the synthesis and study of various

    molecular switchers

    and

    molecular wires.

    The lattercan have quite unusual structures. An example is poly-diacetylene encapsulated in polysaccharide shizofillanwith a resulting spiral structure.

    The creation of a diversified spectrum of switchersand nanowires gave us the opportunity to form logicaldevices on their basis. We assume that a new moleculartechnology will appear by 20202025. In addition,

    quantum computers will appear in another 1020 years.The architecture of such a molecular computer isassumed to be similar to a silicon computer. However,logical gates and smart molecules carry out logical con-nections between individual elements of this computer.

    The elemental base of molecular computers is

    bistable molecular

    and

    supramolecular structures

    These are structures that exist in two (or several) ther-modynamically stable states, met by local minima on

    Nanoreactors

    Photonic crystals

    Phonon glass

    Devices for quantumcomputers Nano- and microcontainers(target delivery)

    Nanobots

    Molecular machines

    Hydrogen and methane accumulators

    Phononic scatteringon quest oscillations

    Conductingframe

    ~ 1415

    Supramolecularsystems

    Fig. 1.

    Expected practical results of supramolecular chemistry.

    Fig. 2.

    Main stages of the development of molecular electronics.

    1970 1980 1990 2000 2010 2020

    1974A. Aviram,M. RatherMolecularpn Junction

    D

    (

    n

    )

    A(p)

    Molecularswitches2-D and 3-D molecular memorynanowires

    Molecularlogicalgates

    Creatinga molecularcomputer

    on nanowires

    off

    D

    -

    -

    Molecular junction

    Polyacetylene in the polysaccharideshizofillan shell

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    TARTAKOVSKII, ALDOSHIN

    polyethylene foam. Switching between these states isdone by various external impacts. In terms of informat-ics, such structures may be associated with the notionof logical zero (0) and one (1), and their regroupings,with information transfers.

    Supramolecular formations capable of light-trig-gered reversible regroupings are qualified as photo-chromic systems. An example is chromenic, fulgidic,spiropyranic, and spirooxazine systems, which werestudied in our country by Academicians Minkin,Aldoshin, and Alfimov, Doctor of Chemical SciencesM.M. Krayushkin, and other chemists. They operate atroom temperature and have response times to externalimpacts, that is, reactions of femtoseconds, and equilib-rium times of picoseconds. 3-D optical memorydevices based on these systems ensure a colossal writ-ing density. Even a 532-nm laser writes informationwith a density of 10

    13

    bit/cm

    3

    , and a UV laser increasesthis value by an order of magnitude.

    The first

    3-D optical memory

    devices, multilayerfluorescent disks, were based on indolylfulgides, pho-tochromic compounds first obtained at Rostov StateUniversitys Research Institute of Physical and OrganicChemistry and at the Mendeleev Technological Univer-sity and studied at the Photochemistry Center and theRAS Institute of Problems of Chemical Physics. Thesecompounds, especially 2-indolylfilgides, are character-ized by an exceptionally high thermal stability. Thecyclic form has a fluorescence by which information isread. The bit area on such disks is about hundredths ofa square micron, or 10 000 nm

    2

    . This is the area of thou-sands of molecules. Professor A. Irie from Japan hasshown with a similar system that the bit area can bereduced to the size of one molecule.

    An especially promising trend in the creation of

    materials with ultrahigh magnetic memory

    (one mole-cule, one bit) is the development of monomolecularmagnets. Although magnetism is a collective property,metalloorganic clusters, characterized by (i) the mainhigh-spin state, (ii) a large magnetic anisotropy relativeto the most energy-favorable direction of spontaneousmagnetization, and (iii) the absence of, or weak, mag-netic interactions between molecules, display the prop-erties of a permanent magnet.

    An important indicator is blocking temperature(below which relaxation becomes very slow). At 1.5 K,cluster Mn

    12

    retains magnetization for 40 years, and, at2 K, for two months and only 40% of magnetization.

    The smallest monomolecular magnet produced thusfar contains only five metallic centers. The largest oneis a nanoparticle of 42 nm in diameter.

    Blocking temperatures for all currently knownmolecular magnets do not exceed 3 K, which is prede-termined by very small values of energy barriers.

    The problem of obtaining high-spin clusters hasbeen solved successfully. For example, a cluster hasbeen obtained to have 83 parallel electronic spins in the

    main electronic state. However, the main problem andthe main search direction are compounds with a highanisotropy relative to the axis of easy magnetization.

    The above data indicate considerable progress in thesphere of fast optical molecular switches and high-capacity memory devices. In fact, the maximum possi-ble indicators have been reached at the molecular level:the speed of an elementary response and a writing den-sity of one bitone molecule.

    A way to control these molecular systems to date isthe transmission of electric signals. Therefore, 21st-century chemistry is facing the task of creating

    molec-ular rectifiers

    and

    molecular wires.

    The search for molecules that can conduct electriccurrent is very active indeed. According to theoreticalestimates, such systems can be obtained by designingflat and linear aromatic structures in which the energygap between the lowest free and the highest filled orbit-als is the smallest. Nevertheless, the estimates showthat it will still be higher than 1.5 eV.

    Another search area is oligomeric metallocomplexstructures. The most promising here is porphyrinicpolymers (Academician Tsivadze and RAS Corre-sponding Member O.N. Koifman).

    It is assumed that the best candidates for molecularconductors are linear conjugated oligomeric structureswith a section of about 0.3 nm and a length from 1 to100 nm. Such oligomers were obtained by J.M. Tour(United States), who developed the so-called conver-gentdivergent method to this end. Lengths of 510 nmand the conductivity of self-assembling monolayers(SAMs) adsorbed on the surface of gold electrodes withthiol groups were obtained for molecules of 5 nm inlength. A current density of 50 A/cm

    2

    was reached.An interesting new area is molecular wires with

    insulation. Such conductors are necessary to avoidcross connections in contours. The main approach isencapsulating a conductor in a polymer shell.

    To date, chemistry has achieved wonderful suc-cesses in creating

    nanomaterials

    by the bottomup andtopdown principle. The results obtained in the sphereof nanomaterials are impressive already today.

    Figure 3 shows some materials that are to be intro-duced in less than ten years from now. These are vari-ous ultradisperse catalysts, membrane catalysts, andcarbon nanotube and nanofiber catalysts for variouschemical industries.

    Nanomaterials that are to be introduced later (1020 years from now) are designed for nanoelectronics,nanophotonics, and IT. They are magnetic memorybased on self-organizing magnetic particles, transistorsbased on filled one-wall carbon tubes, and photonicnanocrystals.

    Nanomaterials for biology are mainly at the stage ofbasic research, and their broad introduction is expectedin more than 15 years. Analysis of nanomaterial usesimplies that practically all elements of our life may be

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    related to nanomaterials and nanotechnologies in thefuture.

    A few words about

    coherent chemistry.

    This is anew face of chemistry. Coherence is the property ofchemical systems to form oscillating response modes.Coherence, or response synchrony in time, is a period-ical change in response speed, and it is detected asoscillations in product output, luminescence emission,electrochemical current or potential, etc.

    Chemical coherence exists at two levels: quantumand microscopic. Oscillating and spin coherence is of aquantum origin. The most popular example of macro-scopic coherence is the BelousovZhabotinsky reac-tion.

    Figure 4 shows a quantum oscillating coherence. Ashort laser impulse of 10

    14

    10

    13

    s (its length is smallerthan the oscillation period of atoms) induces a mole-cule and places it in a new potential. A moleculeensemble prepared by a laser impulse behaves coher-ently in this new potential; that is, the atom oscillationsof ensemble members are synchronized, and theensemble itself is a wave packet. As it moves along thepotential surface, the wave packet may fall in severalother packets (with a different oscillation amplitudeand phase); some packets may diphase (lose coherence)and disappear; some may interfere and restore the ini-tial packet; etc.

    Of course, the above picture is simplified, but itclearly illustrates the main ideas of quantum oscillatingcoherence and its chemical effects. The main idea isthat coherent chemistry introduces a new phase factor

    into control over chemical reactions. Changing thephase, we can manipulate the chemical behavior ofensembles of reacting particles without changingmotion energy or momentum.

    Another new sphere of contemporary chemistry is

    spin chemistry,

    which studies the behavior of the angu-lar momenta (spins) of electrons and nuclei in chemicalreactions (Fig. 5). Spin chemistry is based on a funda-mental law: the spin of electrons and nuclei in adiabaticchemical reactions is strictly preserved; only thosereactions are allowed that do not require spin change.

    Ultrafine catalysts

    Carbon nanotubeand nanofiber catalysts

    200 nm

    Al

    2

    O

    3

    Al

    Fig. 3.

    Nanoindustry and the chemical industry.

    6.9

    Na

    I

    Na

    Na

    Na

    +

    Na

    +

    I

    I

    I I

    Ionic state:

    Na

    +

    + I

    Fig. 4.

    Quantum oscillating coherence of wave packet Nal.

    Membrane catalysts

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    In other words, all chemical reactions...