Natalya V. Abramova

Photochemical and photophysical properties ofmeso-tetraferrocenylporphyrin. Quenching ofmeso-tetraphenylporphyrin by ferrocene

It was found that the quantum yield of the fluorescence ofmeso-tetraferrocenylporphyrin (TFcP) is at most 3.0·10−5, and that of the triplet state of FTcP is at least 200 times lower than the quantum yield ofmeso-tetraphenylporphyrin (TPP). Excitation of TFcP in CCl4 by light with λ>410 nm results in the oxidation of TFcP. The singlet and triplet excited states of TPP in toluene and acetonitrile are quenched by ferrocene with rate constants of 1.2·1010 and 1.7·1010, (4.6±0.5)·108 and (1.37±0.21)·109 L mol−1 s−1, respectively. The quenching mechanisms are discussed.

Complexes ofmeso-tetrametallocenylporphyrins with ZnII ion and their stability constants with imidazole

Recently we have obtained the first representatives of a novel class of porphyrins containing metallocenyl groups (ferrocenyl, ruthenocenyt, and cymantrenyl) in mesopositions. 1-3 A direct bond of the macroheterocycle skeleton to the metallocenyl fragments with their specific geometry and reactivity opens up new possibilities tor obtaining porphyrins and their metal!ocomplexes with useful practical properties. The constants of equilibrium of the formation of the extraligand complexes are important characteristics of porphyrin metallocomplexes, determining their behavior in various processes. In this work, complexes of the Zn 1I ion with tetracymantrenylporphyrin (I) , qtetraferrocenylporphyrin (2), and tetraruthenocenylporphyrin (3) are first described, and the stability constants (Kst) of extraligand metallocomplcxes i a -3a with imidazole (lm) have been determined. Complexes la--3a were obtained by interaction of porphytins 1--3 with zinc acetate or zinc chloride in DMF in 85-90% yield and characterized by tH NMR, electronic and mass spectra (FAB). UV spectra (CHCI3) , Lmax/nm: la -464, 559. 595, and 643; 2a -436, 618. and 673: 3a -438, 599, and 647. JH NMR (200 MHz, CDCI3), 8: la -9.67 (s, 8 H. [I-H): 5.79 (m. 8 H, Cp): 530 (m, 8 H, Cp); 2a -9.84 (s, 8 H, 13-H): 5 37 (m, 8 H, Cp): 4.30 (m, 8 H, Cp): 4.07 (s, 20 H, Co); 3a -9.79 (s. 8 H. ~-H): 5.71 (m, 8 H, Cp): 5.05 (m, 8 H, Cp): 4.40 (s. 20 H, Cp). MS (FAB), re~z:., la -1181 [M+HI+; 2a -1108 [M-l; 3a -1292 [M*]. Samples l a 3 a used for determination of K a were additionally purified by column chromatography on A120 3 (Brockmann II activity, benzene), reprecipitated from saturated solutions in benzene or chloroform with cooled hexane, and dried in vacuo. The /(st values for the extraligand complexes of compounds l a -3a with Im and that for zinc tetraphenylporphyrinate (4) (taken as the standard) were obtained by the method of spectrometric titration in benzene at two wavelengths and at 25 ~ on a Specord UV-VIS instrument. The formation of extracomplexes (EC) is accompanied by a bathochromic shift of all absorption bands of the porphyrin chromophore and by a change in their relative intensities. As the metatlocomplex (MC) : l m ratio changes in the range from 1 : 0.1 to 1 : 500, several isobestic points are observed in the spectra of the mixtures. They are indicative of the formation of monoligand EC in the solution and existence of an equilibrium of the type:

Synthesis and spectral properties of mixedmeso-metallocenylporphyrins

A series of mixed porphyrins with different numbers of metallocenyl (ferrocenyl and cymantrenyl) and aryl (Ph and C6F5) groups at themeso-positions was obtained and characterized by1H NMR, electronic absorption, and mass spectra. The downfield shift of NH signals as well as the bathochromic shift ofQ-bands can be attributed to a distortion of the porphyrin macrocycle upon the introduction of bulkymeso-substituents.

Femtosecond dynamics of relaxation of photoexcited meso-tetraferrocenylporphyrin in the nonprotonated and diprotonated forms (Fc4PH2 and Fc4PH42+)

The relaxation of the Q1(π—π*) excited state of the nonprotonated Fc4PH2 and diprotonated Fc4PH42+ forms of meso-tetraferrocenylporphyrin was studied by femtosecond laser absorption spectroscopy. Transition from the Q1(π—π*) state to the charge-transfer state was shown to occur within 208±10 fs for Fc4PH2 and 9±3 ps for Fc4PH42+. A fast vibrational relaxation with a characteristic time of 120—140 fs was found for both forms. The relaxation time of Fcδ+—Pδ– charge-transfer state for Fc4PH2 was 17±4 ps.