Travaux du bureau international d’étalons physico-chimiques

All-trans-octatetraene 3,10-di(tert-butyl)-2,2,11,11-tetramethyl-3,5,7,9-dodecatetraene emits fluorescence in three different regions of the visible spectrum. Thus, it produces an extremely weak emission in the gas phase that can hardly be detected in the condensed phase; such an emission exhibits a negligible Stokes shift with respect to the 1A(g)-->1B(u) absorption transition and can, in principle, be assigned to the 1B(u)-->1A(g) emission for the compound. A second, structureless fluorescence emission, centered in the region of 525 nm, is observed in the gas phase and at somewhat higher wavelengths in the condensed phase [viz., 570 nm in 2-methylbutane (2MB) and 550 nm in squalane (SQ)]. While detectable, this emission increases significantly, with no change in spectral position, as the solution temperature is lowered; also, it is abruptly replaced by a new, strongly blueshifted emission at approximately 490 nm in 2MB and 455 mm in SQ when the viscosity of the medium exceeds a given level. The fact that the two fluorescence emissions considerably depart from the expected behavior for a 1B(u)-->1A(g) emission in an all-trans-polyene, and that one disappears while the other simultaneously appears as the medium becomes more rigid, suggests that the two emissions are produced by two different molecular structures and that the rigidity of the medium switches their production from the originally excited all-trans 1B(u) form. The observed spectral behavior is consistent with a recently proposed model [J. Catalan, Chem. Phys. 335, 69 (2007)] in which the 1B(u) excited state of octatetraene can give two distinct molecular conformers as a result of twisting about different C-C single bonds.

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“…The viscosity of 2MB at 15°C, 0.234 cP, 28 is quite similar to that of its isomer n-pentane at the same temperature ͓0.241 cP Ref. 29͔.…”

Section: Emission In 2mbmentioning

confidence: 73%

New contributions to the photophysical model for all-trans-polyenesfrom ttbP4, a nonphotolabile octatetraene

Catalán

Hopf

Martus

2008

The Journal of Chemical Physics

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“…As an illustration, the following example may be reported. Benzene saturated with water at 25° C contains aroun~ 0.1 percent of water and has a refractive index lower by 0.000 14 than benzene, water-free, whereas a change in temperature of 1°C causes a change in the refractive index nif of 0.00063 [20]. From all of the measurements made, the refractive index of benzene at 25° C for the sodium line D may be taken as 1.49807 ± 0.00006.…”

Section: T Ab Le I -Properties Of the Preparations Of Benzenementioning

confidence: 99%

Measurements of certain physicochemical constants of benzene

Wojciechowski¹

1937

J. RES. NATL. BUR. STAN.

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“…THE best cyclohexane available through most of the leading chemical dealers has a freezing point between 3.5°and 4.5°C. Timmermans (13) and others have shown that the freezing point of the pure substance lies close to 6.4 °C. Since the physicochemical properties of the hydrocarbon make it a useful solvent for many purposes, a simple method of purification seemed highly desirable.…”

mentioning

confidence: 87%