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Laurea specialistica in Scienza e Ingegneria dei Materiali

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Presentation on theme: "Laurea specialistica in Scienza e Ingegneria dei Materiali"— Presentation transcript:

1 Laurea specialistica in Scienza e Ingegneria dei Materiali
Curriculum Scienza dei Materiali Chimica Fisica dei Materiali Avanzati Part 8 – Molecular switches and molecular machines Corso CFMA. LS-SIMat Corso CFMA. LS-SIMat

2 Molecular-level devices
Molecular-level electronic components Molecular-level systems that play the same functions played by macroscopic components in electronic devices Molecular-level mechanical machines Molecular-level systems that perform mechanical movements analogous to those observed in macroscopic machines Molecular-level electronic components Molecular-level mechanical machines Molecular wires Molecular switches Molecular antennas Charge-separation devices Molecular memories Molecular sensors Molecular logic gates Molecular tweezers, doors and boxes Rotary motors Piston/cylinder systems Molecular shuttles and muscles Sliding molecular rings Corso CFMA. LS-SIMat

3 Switching of electron or energy transfer processes
e- or E A C Switching requires an external stimulus which, at the molecular level, causes electronic and nuclear rearrangements. Usually one of the two types of rearrangements prevails or is more relevant to the performed function. The three main types of stimuli that can be used to switch a chemical compound are: Light energy (photons) Electrical energy (electrons or holes) Chemical energy (in the form of reactants) Corso CFMA. LS-SIMat

4 Molecular switches A molecular switch is a system on the molecular scale which can be reversibly brought from one state into another by means of an external stimulus. Important properties for practical applications: thermal irreversibility quick response high efficiency fatigue resistance nondestructive readout Corso CFMA. LS-SIMat

5 Example: diarylethene switches
First described by Irie in 1988. M. Irie, M. Mohri, J. Org. Chem. 53 (1988), Reaction is thermally irreversible, response is quick, efficiency and fatigue resistance are high. Many studies have been performed on diarylethenes, with as main goals improving the switching properties and achieving non-destructive read-out. For an extensive review, see: M. Irie, Chem. Rev. 100 (2000), Corso CFMA. LS-SIMat

6 Photochromic response of diarylethene
A very broad absorption extending over most of the visible range appears upon UV irradiation and ring closure The process can be reversed by irradiation with l > 500 nm Corso CFMA. LS-SIMat

7 Mechanism: increase of the conjugation
Open ring, parallel conformation Open ring, antiparallel conformation Closed ring Corso CFMA. LS-SIMat

8 Other photochromic switches
Cis-trans isomerization of azobenzenes Switching of a spiropyran derivative (c = closed, o = open) Photochemical transformations of fulgides Corso CFMA. LS-SIMat

9 Optical memories by holographic recording
Holographic optical storage is a unique method for achieving high-density data storage in three dimensions. Photopolymer systems are quite attractive because of their high sensitivity, ease of preparation, and self-development capability. Rewritable holographic recording materials based on photochromic conversion have attracted strong interest for three-dimensional optical recording Holographic writing set-up A phase hologram with Dn = 1.15x10-3 and period dependent on the angle 2 is written. Photochromic cyclability Corso CFMA. LS-SIMat

10 n * N R O C H Methacrylic backbone
3 2 Methacrylic backbone Optically active cyclic group Conjugated trans-azoaromatic chromophore R = CN, NO2 poly[(S)-MAP-C] R = CN Mn=43,900Mw /Mn=1.4 Tg=192°C Td= 311°C poly[(S)-MAP-N] R = NO2 Mn=18,300Mw /Mn=1.4 Tg=208°C Td= 315°C

11 488 nm 633 nm Absorption in the visible: azo-dyes n *, * and CT el. trans.

12 h  Photoinduced trans  cis  trans isomerization cycles Ē trans cis
rotational diffusion h STOP trans cis

13 Reversible photoinduced orientation of azobenzene groups


15 irradiation with CP-L light
Reversible inversion of the CD signal by irradiation with CP-L light poly[(S)-MAP-N] Tg = 208 C thin films 100  300 nm I  160 mW/cm2 x 60 s L. Angiolini et al., Chem. Eur. J., 8 (2002) 4241


17 Switching of electron transfer by a photon input
Light switching of electron transfer in multicomponent molecular systems based on the 1,2-bis-(3-thienyl)-ethene photochromic bridge In the closed form energy is transferred to the conjugated diarylethene unit instead of electron transferred to the pyridinium ion Corso CFMA. LS-SIMat

18 Multistate-multifunctional supramolecular systems
Multistate systems : compounds that can be reversibly interconverted between more than two stable states Multifunctional systems : compounds that can be reversibly interconverted between stable states by means of different stimuli Two photochromic units can be coupled in the same supramolecular species, giving biphotochromic multistate systems The photochemical inputs used to stimulate photochromic compounds can be couped with several other types of stimuli, leading to a variety of interesting multistate-multifunctional systems On application of n independent stimuli, each related to 2 states, 2n different states of the system become available in principle Corso CFMA. LS-SIMat

19 Towards molecular logic gates
Corso CFMA. LS-SIMat

20 Electronic vs. ‘chemical’ computers
Corso CFMA. LS-SIMat

21 Molecular-level machines
A molecular machine is a particular type of a molecular device whose outcome is a mechanical motion, i.e., in which the component parts can be set in motion as a result of some external stimulus What are the possibilities of small but movable machines? [...] Lubrication might not be necessary. Bearings could run dry; they wouldn’t run hot because heat escapes from such a small device very, very rapidly. [...] An internal combustion engine of that size is impossible. Other chemical reactions, liberating energy when cold, can be used instead. [...] What would be the utility of such machines? Who knows? [...] I cannot see exactly what would happen, but I can hardly doubt that when we have some control of things on a molecular scale we will get an enormously greater range of possible properties that substances can have, and of the different things we can do. R. P. Feynman, Address to the American Physical Society, December 1959 Corso CFMA. LS-SIMat

22 Natural Molecular Machines and Motors
Cells have hundreds of different types of molecular motors, each specialized for a particular function. Many biological motor-like proteins have been discovered and characterized in recent years. (Natural) molecular motors come in a wide variety of designs. Some motors operate in a cyclic fashion, undergoing a number of steps that correspond to changes in conformation and/or in chemical state, and eventually resetting themselves to their initial configuration. C. Bustamante, D. Keller, G. Oster, Acc. Chem. Res., 2001, 34, Copernicus, Springer - Verlag, New York, 1996 Corso CFMA. LS-SIMat

23 Natural Molecular Machines and Motors - 2
Rotary motor proteins ATP Synthase Bacterial flagellar motor Linear motor proteins Myosin Kinesin Dynein Corso CFMA. LS-SIMat

24 Artificial molecular machines: molecular tweezers
Macroscopic tweezers Molecular tweezers (photochemically controlled) S. Shinkai et al., J. Am. Chem. Soc., 1981, 103, 111 Corso CFMA. LS-SIMat

25 Photocontrolled Opening-Closing of Molecular Cavities
Azobenzene containing macrotricyclic receptors Azobenzene capped β-cyclodextrin Corso CFMA. LS-SIMat

26 A Photochemically Driven Molecular Rotary Motor
B.L. Feringa et al., Nature, 1999, 401, 152 Corso CFMA. LS-SIMat

27 Photochemically Driven Threading-Dethreading Motions in Pseudorotaxanes
Corso CFMA. LS-SIMat

28 Undirectional Circumrotation of Macrocycles in Catenanes
Corso CFMA. LS-SIMat

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