Optical memory effects

Soon after the initial discovery of ferro-electricity in chiral smectic LCs it was predicted that, if the helix of an SmC phase were suppressed by surface forces in very thin layers between two glass electrodes, then this would pin the molecules in their positions and allow switching between two energetically equivalent polarization directions, thereby giving rise to an electro-optic memory effect [22]. This is the basis of the electro-optic display device called the surface stabilized ferroelectric liquid crystal... 

Magnetooptic Materials. The appHcation of magnetooptic effects to optical memory systems, such as for laser beam writing and magnetooptic read, has been the subject of much research. Magnetooptic storage media offer the potential of storing over 120 Mbit/cm of information without contact of the read/write head which would thus be very competitive to floppy disks and tape. 

Rychnovsky et al. considered the formation of achiral conformers from chiral molecules and trapping the prochiral radical with a hydrogen atom donor based on memory of chirality (Scheme 12) [41], The photo-decarboxylation of optically active tetrahydropyran 40 leads to an intermediate 43, which now does not contain a stereocenter. If the intermediate 43 can be trapped by some hydrogen atom source before ring inversion takes place, then an optically active product 41 will be formed. This is an example of conformational memory effect in a radical reaction. It was reported that the radical inversion barrier is low (< 0.5 kcal/mol) while the energy for chair flip 43 44 is higher (5 to... 

One of the properties of a class of materials known as chalcogenide glasses is that they exhibit a wide spectrum of photoinduced effects. Photoinduced phenomena have recently been extensively studied (see corresponding references in previous sections), partly as an interesting subject for fundamental research in the field of disordered sohds and partly due to the potential apphcation of these phenomena in opto(photo)electronics (xerography and xeroradiography, optical memories, optical circuits, photoresists, etc.). 

These effects open up the possibility of novel magneto-optical memory devices. 

Magaemaptic Materials. The application oT magncMoplte effects to optical memory systems, such as lor laser beam writing and mngnclonplic read, has been the subject of much research... 

In 2008, Sakamoto and coworkers have reported the synthesis of optically active (3-lactams via photochemical intramolecular y-hydrogen abstraction reaction of thioimides [177]. This reaction provides the first example of a chiral-memory effect for the photochemical y-hydrogen abstraction reaction of thiocarbonyl or carbonyl compounds, and a useful synthetic methodology for preparing optically active (5-lactams (Scheme 78). 

Series of studies by Huang et al. as well as Puchkovska and co-workers concentrated on electro-optic effects induced by the addition of organoclays to 5CB. Puchkovska et al. reported on electro-optic contrast and memory effects as a... 

The PR effect was first observed in 1966 as an undesirable effect in an EO crystal, LiNb03 [1], It was soon realized that this effect is reversible and its PR mechanism was then identified [2,3], These PR materials can be applied to high-capacity optical memories, dynamic hologram formations, massive interconnections, high-speed tunable filters, and true-time relay lines for phase array... 

In a similar way, the video disk reconverts the signal produced by the Kerr effect on a thin film of an amorphous substance such as Tb-Fe sputtered on a substrate disk made of plastic or glass. The Tb-Fe film functions like a perpendicular magneto-optical memory... 

Matsumura and co-workers reported a memory effect of chirality in the electrochemical oxidation of 95 to give 96, although the enantioselectivity was modest (Scheme 3.25). The reaction is assumed to proceed via carbenium ion intermediate Q.46 The mechanism for asymmetric induction is not clear. A possible mechanism involves chiral acid (95)-mediated deracemization of racemic 96 produced by the electrochemical oxidation of 95. However, this suggestion may be eliminated based on the finding that treatment of racemic 96 with 95 in methanol containing 5% formic acid did not produce optically active 96. 

In principle, this mode of operation creates the possibility of producing high-information-content displays due to the short frame times associated with bistable displays, since they are basically a memory effect and only new information must be changed. Unfortunately, metastable twist states of intermediate twist, which degrade the optical performance of the device, form around dust particles in cells with a cell gap below a certain value (d < 20 m). Therefore, since the response time is proportional to d, very long response times are observed ( 1 s) for LCDs with a cell gap above this critical value. These optically disruptive metastable twist states also form at the interface with spacers used to generate a uniform cell gap. 

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