Delayed Luminescence of 8-Aza-D-Homogone-1,3,5(10),13-Tetraene-12,17a-Dione in the Gas Phase and Solid Solutions

Abstract

It is shown that the delayed-luminescence spectrum of 8-aza-D-homogone-1,3,5(10),13-tetraene-12,17a-dione (8-aza-D-homogonane) in the gas phase comprises a band of thermally activated delayed fluorescence and a band of annihilation delayed fluorescence that are respectively due to the C-and D-centers representing products of photo-and thermotransformations of the initial steroid for which we failed to detect delayed luminescence. The triplet-triplet energy transfer from the C-centers to the D-centers has been detected and its efficiency has been determined. It has been established that, in a frozen hexane solution (T = 77 K) of the substance taken from a vacuum cuvette after the investigation of initial 8-aza-D-homogonane in the gas phase, only the C-and D-centers phosphoresce. For a frozen solution of the initial steroid in a vitrifying mixture of tetrahydrofuran and toluene, a phosphorescence of both the steroid itself (λ max phos = 415 nm) and the C-and D-centers (λ max phos = 498 and 532 nm, respectively) was detected. This indicates that even the initial steroid kept at room temperature contains products of its transformation whose concentration increases on irradiation and heating. The C-and D-centers are stable molecules.Introduction. According to the data of [1], 8-azasteroids are biologically active organic compounds that can stimulate or oppress the immunity of living organisms; therefore, investigations of the photophysical and photochemical processes occurring in steroid molecules are of importance.The first compound of the steroid series whose delayed luminescence was detected was 2,3-methoxy-8-azagona-1,3,5(10),13-tetraene-12,17-dione. Microcrystals of this compound excited by radiation with λ exc = 250 nm and heated to a temperature of T = 293 K show not only fluorescence but also phosphorescence with a maximum wavelength of λ max phos = 470 nm and a duration of τ = 280 µsec. On excitation of a frozen solution of the indicated

Luminescence of biologically active 24-epicastasterone and a model compound

“…A mechanical two-disk phosphoroscope was used to record the phosphorescence spectra. The phosphorescence lifetime was measured 1 on an automated laser spectrometer [11].…”