Influence of a Solvent on the Quantum Yield and Duration of the Fluorescence of Tetraazoporphin

Abstract

ev UDC 535.37In view of the discrepancies between the values available in the literature for the photophysical parameters of tetraazaporphin in solutions, we measured its quantum yield and duration of fluorescence in a number of solvents. It has been found that alcohols (isobutanol and isopropanol) quench the fluorescence appreciably. For a solution in toluene -a stable chemically inactive and low-polar solvent -the measured quantum yield of the fluorescence of tetraazaporphin is equal to 0.180 ± 0.015 and its duration is 3.4 ± 0.1 nsec.Keywords: tetraazaporphin, quantum yield of fluorescence, fluorescence duration.Introduction. The tetraazaporphin (H 2 TAP) molecule, or porphyrazine, is one of the fundamental structures in the porphin series, which is an intermediate between the biologically important class of porphyrins and classical dyes of the type of phthalocyanine, which are finding wide application in various fields of science and technology.In investigating the effect of hydrogenation of pyrrolic rings in porphyrazine macrocycles on the photophysical properties, in [1, 2] the quantum yield of fluorescence (ϕ F ) of H 2 TAP was measured as a basis for comparison with the data on dihydroderivatives. By comparing our results with the data of earlier investigations [3-6], we found that there were noticeable discrepancies between the values of ϕ F measured by various authors and also between the data on durations of fluorescence τ F . In [3,4], it was found that ϕ F = 0.12 and τ F = 3.7 nsec (see also the review [7]), in [5], ϕ F = 0.16 and τ F = 6.4 nsec; in [6], ϕ F = 0.12. Recently,in [8], the value ϕ F = 0.29 was obtained for H 2 TAP, whereas in [1, 2] ϕ F = 0.19 and τ F = 3.3 nsec.Since different solvents were used in the works cited, the idea arose that the quantity ϕ F of H 2 TAP can substantially depend on the nature of the solvent. The aim of the present work is to elucidate this influence and to arrange in an ordered fashion the data on the values of ϕ F and τ F for H 2 TAP.Experimental. Measurements of the quantum yield of fluorescence were performed by a relative method from the ratio between the areas of the fluorescence spectra of an object and a standard determined in terms of "quantum" intensities (I λ /hν) on an SDL-2 automated spectrofluorimeter (USSR) consisting of an MDR-12 light-transmission excitation monochromator and an MDR-23 registration monochromator. The excitation and registration axes were arranged at an angle of 90 o . A DKsSh-120 xenon lamp was used as the source of excitation. The light signal separated by the monochromator was registered with the aid of an FÉU-100 cooled photomultiplier (spectral range 200-800 nm) operating in the regime of photon counting. The spectral sensitivity of the recording monochromator-FÉU system was corrected with the aid of a TRSh 2850 standard ribbon tungsten lamp. The spectral width of the excitation monochromator slit did not exceed 4.8 nm in the entire spectral range studied, and that of the registration monochromator -2.6 nm in the 400-800-nm ...

Origin of the Red-Shifted Optical Spectra Recorded for Aza-BODIPY Dyes

“…The same effect is found for related aza-BODIPY dyes and with other hydrogen-bond donors, including water, and counts against using aza-BODIPY dyes as sensitizers in aqueous media. It might be noted that a similar effect was reported earlier for aza-porphyrins, where it was observed that isobutanol shortened the excited singlet state lifetime to 1.5 ns compared to a value of 3.4 ns found in toluene, and was explained in a similar manner. Interestingly, ethanol has only a marginal effect on the excited singlet state lifetime of a highly constrained analogue of aza-BODIPY, where attachment to the meso -aza N atom is partially blocked by aryl substituents at the 1,7-positions.…”

The fluorescence and electronic structure of phenyl-substituted tetraazachlorin molecules

“…(Only the τ F value was reported in our earlier detailed publica tion [10].) Because of the discrepancies taking place in the literature concerning ϕ F data for H 2 TAP, we mea sured (with tetraphenylporphine in toluene as the standard) and for an H 2 TAP solution in toluene (ϕ F = 0.18, τ F = 3.4 ns) and in some other solvents [24]. These measurements are in satisfactory agree ment with earlier reported data ( Table 1).…”

Luminescence of In(III)Cl-etioporphyrin-I

“…Quantum yields of fluorescence (ϕ F ) and singlet oxygen of luminescence (ϕ ∆ ) at room temperature were determined by the relative method with toluene solutions of tetraazaporphin (ϕ F = 0.18) [28] and Pt-dibenzo-tetraaza-iso-bacteriochlorin (ϕ ∆ = 0.72) [29] as standards, respectively. The phosphorescence quantum yields ϕ P at 77 K were calculated relative to the fluorescence quantum yield ϕ F using the ratio of the areas under the fluorescence and phosphorescence spectral curves.…”