Reversible Formation and Eradication of Colors by Irradiation at Low Temperatures. A Photochemical Memory Model

Hirshberg, Yehuda

doi:10.1021/ja01591a075

Cited by 281 publications

(148 citation statements)

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“…InDMD and TMD the situationisdifferent. As lang ago as 1956 Hirshberg 20 described a coloured isomer of DMD resuJting from u.v. irradiation of solutions in a toluene-alcohol mixture, and partly erasable by irradiation with 'visible' light.…”

Section: Resultsmentioning

confidence: 99%

Dianthrone photochromism 1950-1970

Bercovici¹,

Korenstein²,

Muszkat³

et al. 1970

Pure and Applied Chemistry

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Photachromie phenomena are very briefly surveyed, with special emphasis on reversible photocyclizations on which many photochromic phenomena are based.The chromic behaviour of dianthrone. DA. and its derivatives is reviewed. It is suggested that the coloured modification B is common to all cases observed, and that it is identical with the thermochromic coloured form.A detailed study of the reversible and irreversible photoreactions, thermal reactions, and emission properties of DA and its derivatives is reported, based on the use ofboth stationary and flash methods, in a wide range oftemperatures and solvents. All compounds are fluorescent and phosphorescent, and their triplet-triplet absorption spectra and triplet decay were observed at sufficiently low temperatures. With increasing temperature the triplet decays mainly via its conversion into B, in some cases via a precursor D. Both triplet -D and D-B are strictly viscosity-controlled reactions. At still higher temperatures those derivatives not substituted in the 1 and 1' positionsundergo irreversible photoreactions in competition with the formation of B. B itself is not affected by irradiation, apart from the low yield thermally-reversible formation of a free radical. Electron spin resonance measurements confirm the absence of any correlation between photochromism and e.s.r. signals.In the derivatives substituted in the 1 and 1' positions, only Bis produced. However, at still higher temperatures, and only in compounds methylated in the 1 and 1' positions, a second coloured modification Cis formed in competition with B. The ratio [C]/[B] is strongly dependent on the nature of the solvent, the temperature, and the wavelength of the photoactive light. The latter effect is due to the reverse photoreaction C ~ A, which is characteristic for the C form. This property of C was used in order to determine its absolute absorption spectrum in various solvents. The quantum yields of photocoloration are around 0.6 and decline to practically zero at very high viscosities, while the quantum yield of photoerasure of C is about 0.05 but goes down with the temperature only to a limited extent.Low-temperature n.m.r. and i.r. measurements of B and C were carried out. The tempting proposal that B has the cyclic structure analogaus to 4a,4b-dihydrophenanthrene cannot be upheld in view of the thermal and photochemical stability of B towards oxygen. It may hold for the C isomer, and could explain the n.m.r. results obtained for C. The cyclic structure should be an intermediate in the photo-oxidation of DA to helianthrone, but has as yet tobe detected. The structure of B thus remains open for discussion.The fluorescence of substituted dianthrones is blue-shifted on cooling, again in what seems to be a pure viscosity effect, pro bably connected with steric relaxat In memoriam Yehuda Hirshberg, 1903Hirshberg, -1960 t This is Part VI in the series 'Photochromism in Dianthrone and Related Compounds '. Part of the material described here has been published in two preliminary not...

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Section: Resultsmentioning

confidence: 99%

Dianthrone photochromism 1950-1970

Bercovici¹,

Korenstein²,

Muszkat³

et al. 1970

Pure and Applied Chemistry

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“…Already in his early work Hirshberg envisaged the suitability of such compounds as photochemical erasable memory. 62 Well-known photochromic compounds, spiropyrans or spirochromenes, are characterized by the presence of two heterocyclic parts linked to each other through a tetrahedral carbon atom. The two halves of the molecule are located on two perpendicular planes.…”

Section: Photoswitchable Receptors Based On Spiropyransmentioning

confidence: 99%

Molecular switches as photocontrollable “smart” receptors

2012

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This critical review focuses on the development of photochromic compounds as sensors for cations, anions, and biologically important molecules. The review commences with a brief description of photochromism and the strategies to exploit photochromic molecular switches' properties for sensing application. This is followed by a summary of photoswitchable receptors emerged to date and classified according to the photochromic structure they are based on. These include azobenzenes, fulgides, dithienylethenes, dihydroindolizines, chromenes and spiropyrans.

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“…Among the class of molecular 4 switches, spiropyrans have been probably the most extensively studied over the past several decades owing to the profitable applications they could be used for. Already in his early work Hirshberg envisaged the suitability of such compounds as photochemical erasable memory [14]. Furthermore, optical molecular switches have attracted much attention as a result of their potential use in optical data storage and digital processing [9], sensing [15] and photoregenerable surface modifications [13].…”

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confidence: 99%