No abstract

New Pd(II) and Pt(II) complexes with a highly electron-deficient ligand (H2 PcF64 ) were conveniently prepared in a three-step synthesis. This is the first time that the phosphorescence of phthalocyanines with a H2 PcF64 framework has been measured. Based on these measurements, the triplet-state energies (ET ) were directly determined. Transient absorption experiments revealed broad T1 →Tn absorption spanning from ca. 350 to ca. 1000 nm and allowed determination of the triplet-state lifetimes. Removal of the Pd or Pt from the perfluoro-phthalocyanine resulted in a significant increase of the triplet lifetime for H2 PcF64 . The very efficient intersystem crossing observed for both PdPcF64 and PtPcF64 leads to residual fluorescence and suppresses the fluorescence lifetimes to less than 50 ps. The absence of Pd and Pt in the perfluoro-phthalocyanine ligand, viz. H2 PcF64 , led to a recovery of fluorescence. Cyclic voltamperometry studies pointed to complete resistance of PdPcF64 and PtPcF64 to oxidation and very strong electron affinity, which rendered these materials very good electron acceptors (n-type materials). The presence of d-orbital metals such as Pd(II) and Pt(II) in the phthalocyanine ring stabilizes their reduced forms, as indicated by the spectroelectrochemical experiments. PdPcF64 and PtPcF64 easily sensitize singlet oxygen production with very high quantum yields. Both phthalocyanines presented resistance to photodegradation in the solid state under aerobic conditions and under intense irradiation.

The delayed fluorescence spectrum for 8-aza-D-homogonane in the gas phase consists of a band of E-type delayed fluorescence of M-centers and a band of P-type delayed fluorescence of L-centers being the products of photo- and thermotransformations of a basic steroid. Triplet-triplet energy transfer from the M-centers to the L-centers is established and its efficiency is determined. For 8-aza-D-homogonane in frozen hexane solutions at T=77 K only the phosphorescence of the M- and L-centers is revealed. The phosphorescence of the basic steroid itself (lambda(max)(phos) = 415 nm) as well as that of the M- and L-centers (lambda(max)(phos) = 498 and 532 nm, respectively) is seen in a mixture of frozen tetrahydrofuran and toluene solutions. This is evident of the fact that the basic steroid has the products of its transformations, whose amount grows due to irradiation and heating. The M- and L-centers are stable molecules.

No abstract

Extensive studies of the spectral-luminescent characteristics of four 8-azasteroids and a model compound 2- (3,3-dimethyl-1,2,3,4-tetrahydro-1-isoquinolidene)-5,5-dimethyl-1,3-cyclohexanedion in the gas phase have been made. From the analysis of the dependences of the absorption spectra on the vapor pressure (T low ) and the fluorescence spectra on T low and the exciting radiation wavelength (λ exc ) a conclusion on the presence in the vapors of the investigated 8-azasteroids of three absorption and fluorescence centers (S-, M-, and L-centers) has been drawn. The absorption spectra of these centers strongly overlap. Their long-wave absorption boundaries have been determined. The dependence of the fluorescence spectra of all three centers on λ exc , which is inherent in rarefied gases of individual organic molecules, is observed. The S-centers are the molecules of the initial steroids, and the M-and L-centers are the molecules of thermo-and phototransformations of the initial steroids. The model compound in the gas phase is characterized by the same dependences of the fluorescence spectra on T low and λ exc as those inherent in 8-azasteroids. Taking into account the additional data obtained as a result of investigation of the absorption and fluorescence spectra of solutions of the substances extracted from vacuum cells after the investigation of 8-azasteroids and the model compound in the gas phase, conclusions on the nature of the M-and L-centers have been drawn.Introduction. The organic complexes of the series of 8-azasteroids feature biological activity and can stimulate or suppress the immunity of living organisms depending on their structure [1]. Therefore, investigations of the spectral characteristics reflecting their structure are important.Earlier it was shown that luminescence of 8-azasteroids is observed in different aggregate states: in the gas phase [2], in solutions [2, 3], and in microcrystals [4]. The analysis of the absorption, fluorescence, fluorescence excitation spectra, and duration of the excited states of a water solution (pH 7.4) of 2,3-dimethoxy-8-azagona-1,3,5(10),13-tetraene-12,17-dion (hereinafter referred to as 8-azasteroid III) has revealed the existence of two centers emitting a long-wave and a short-wave fluorescence [5]. The fluorescence of 8-azasteroid III and 8-aza-D-homogona-1,3,5(10),13-tetraene-12,17a-dion (hereinafter referred to as 8-azasteroid I) in the neutral solvent hexane has been assigned to three centers of luminescence [6]. Assumptions on the nature of the centers have been made.Investigations of 8-azasteroids in the gas phase, where the influence of the medium is excluded, are of particular importance. In the present paper, for the first time the spectral-luminescent characteristics of vapors of this important class of compounds have been studied. We focused on and studied in most detail 8-aza-D-homogonane-1,3,5(10),13-tetraene-12,17a-dion (8-azasteroid I) obtained by annealing 3,4-dihydroisoquinoline by 2-acetyl-1,3-cyclopentadion by the method described in [17]...