Phosphorescence of palladium and platinum complexes of benzo-fused hydroporphyrazines

Abstract

UDC 535.37 Palladium and platinum complexes of benzo-fused hydroporphyrazines, analogs of phthalocyanine in whose molecules one or two isoindole fragments are substituted by hydrogenated pyrrole rings giving macrocycles of the chlorin, bacteriochlorin, and isobacteriochlorin types, have been synthesized. Phosphorescence in the near IR region has been detected at 291 and 77 K for complexes of tribenzotetraazachlorin and dibenzotetraazaisobacteriochlorin. The energy of the lowest triplet level T 1 has been determined from the positions of 0-0-bands in phosphorescence spectra. As compared to complexes of phthalocyanine, hydrogenation of a pyrrole ring has a stronger influence on the energy of the T 1 level (lowering) whereas hydrogenation of two adjacent pyrrole rings results in a larger S 1 -T 1 gap. The phosphorescence quantum yield and lifetime have been measured. Based on the data obtained, the rate constants of the radiative and non-radiative de-excitation of the T 1 level have been calculated. The highest phosphorescence quantum yield is obtained for Pt dibenzotetraazaisobacteriochlorin (1.7% at 77 K). The influence of the nature of the metal atom on the electronic absorption spectra of metal complexes of benzohydroporphyrazines is analyzed taking into account literature data for bacteriochlorophyll a, metal complexes of bacteriopheophytin a, and chlorophyll-like molecules having less complex structures.Keywords: palladium and platinum complexes, benzohydroporphyrazines, absorption spectrum, phosphorescence spectrum, phosphorescence quantum yield and lifetime, singlet oxygen formation.Introduction. The energy of the lowest triplet state E T 1 is an important physical property of molecules that influences the course of photophysical and photochemical processes. The value of E T 1 can be determined directly by measuring the phosphorescence spectrum. However, the phosphorescence quantum yield is in many instances small. This hinders the measurements, especially if uncontrolled impurities are present.The magnitude of the singlet-triplet gap E S 1 -E T 1 = ΔE ST , where E S 1 is the energy of the lowest singlet state, is approximately transferable in a series of related compounds so that E T 1 can be estimated for the whole series from the values of E S 1 and ΔE ST . For metal complexes of tetrapyrroles (loosely speaking, metalloporphyrins), the search for phosphorescence is best carried out for palladium and platinum complexes, which have higher phosphorescence yields than complexes of other metals.Two of us (E.A.L. and E.A.M.) prepared new compounds of the hydroporphyrazine subclass (porphyrazine is a synonym for meso-tetraazaporphine, H 2 PA H 2 TAP) with benzene and naphthalene aromatic rings fused to the nonhydrogenated pyrrole rings as the nickel and vanadium complexes and several free bases [1][2][3][4].Herein the Pd-and Pt-complexes of benzohydroporphyrazines are prepared. Phosphorescence in the near-IR spectral region is sought and is one of the goals of the synthesis. It is noteworthy that the spectra...

The fluorescence and electronic structure of phenyl-substituted tetraazachlorin molecules

“…The stan dard in ϕ F determination was cresyl violet (oxazine 9) in ethanol (ϕ F = 0.61, as was measured in our earlier study [10] versus 3,6 diamino N methylphthalimide in ethanol, for which ϕ F = 0.46 [12]). In the determi nation of ϕ Δ , the standard was the tribenzotetraaza chlorin complex of platinum in 2 methyltetrahydro furan (MTHF), for which ϕ Δ ≈ 0.66 [6]. Electronic absorption spectra were recorded on Cary 500 Scan UV Vis NIR (Varian, Australia) and Hewlett Packard 8453 (United States) spectrophotometers using rect angular quartz cells with an optical path length of 10 mm.…”

“…The ϕ Δ value measured for H 2 TAP (0.47) exceeds the ϕ ST estimate [21]; therefore, this estimate is low, since ϕ Δ ≤ ϕ ST , as was mentioned above. Check measurements of ϕ Δ using another setup [25] (which was also used in [6]) and another procedure [26] gave ϕ Δ = 0.47 and 0.52 for two different solutions. Note that ϕ Δ for H 2 TAP in benzene was measured by a photochemical method [27] and the ϕ Δ = 0.46 value was obtained, with ϕ F 1 Unfortunately, a number of misprints crept into the text of [21] due to negligence of the authors.…”

“…Our research team has carried out a number of studies on the correlation between the photophysics and struc ture of these molecules. A list of relevant publications is presented in earlier paper [4]) (see also [5,6]). In view of the foregoing, it is of interest to extend the existing approaches to phenyl substituted analogues of Н 2 ТАC.…”

Люминесценция Pd и Pt бензогидропорфиразинов в ближнем ИК диапазоне

“…Спектрально-люминесцентные свойства бензогидропорфиразинов -цинковых комплексов [6] и соответствующих свободных оснований [6,7] -исследовались нашей научной группой. В работе [8] была зарегистрирована БИК-фосфоресценция комплексов палладия и платины с тетраметилтрибензодигидропорфиразином и октаметилдибензотетрагидропорфиразином с соседним расположением гидрированных пиррольных колец. В настоящей работе, чтобы избежать использования громоздких сокращений и длинных названий химических соединений, мы применили (по всему тексту) обозначения: Pd1 и Pt1 -для комплексов замещенного трибензодигидропорфиразина; Pd2 и Pt2 -для комплексов замещенного дибензотетрагидропорфиразина с противоположным расположением гидрированных пиррольных колец (транс-); Pd3 и Pt3 -для их изомеров с соседним расположением гидрированных колец (цис-).…”

Calculation of the electronic structure and spectra for bacteriochlorophyll analogs

“…Such behavior of the Q x (0-0) band is in contrast with its observed position in this same series of metal complexes of porphyrins and chlorins, for which introduction of a metal atom into the center of the macrocycle is accompanied by a significant hypsochromic shift of the long-wavelength Q(0-0) [or Q x (0-0)] band, which increases successively on going from Cu to Ni, from Ni to Pd, and from Pd to Pt [2,3]. The hypsochromic shift of the Q x (0-0) band on going from Ni to Pd in absorption spectra of recently synthesized complexes of dibenzotetraazabacteriochlorin (MDBTABC) with Ni [5], Pd, and Pt [6] was similar in magnitude to that observed for MBPhea and in both instances can be called anomalous. However, the shift is normal on going from Pd to Pt.…”