Some Physico-Chemical Properties of 3:4,Benzpyrene

Abstract

IN contrast with the characteristic fluorescence spectrum (Curve 1) which 3: 4,benzpyrene always emits when it is dissolved in solvents, we have observed three different types of fluorescent spectra (Curves 2, 3, 4) when the hydrocarbon was excited in the solid state. The needles of a commercial benzpyrene (La Roche) emit a green fluorescent light and we call it therefore the ‘green’ form. Curve 2 exhibits a broad rather symmetrical band with its flat maximum between 500 and 510 m.μ. On pouring an acetone solution of the green form of benzpyrene into cold water there results the well-known colloidal suspension of benzpyrene which emits a yellowish fluorescence. The spectrogram of this ‘yellow’ form has its maximum between 530 m.μ and 540 m.μ, and a typical inflection at the short wave-length side of the band (Curve 3). On heating the green form in an evacuated tube, a white sublimate is formed on the tube walls which fluoresces brightly blue. The spectrogram of this ‘blue’ form shows a maximum between 445 m.μ and 450 mμ, and an inflection on the short-wave-length side which appears as a contrast band at about 425 m.μ (Curve 4). The sublimed crystals are small plates with typically curved edges. We believe that they are identical with the modification of benzpyrene which Iball² obtained from a solution in amyl acetate. According to his X-ray analysis, they are orthorhombic, while the needles (our green form) belong to the monoclinic system. Iball did not examine the fluorescence of either form.