given there)~ Quantitative spectra of triplet--triplet absorption have been determined using ... triplet--triplet absorption of the free base of phthalocyanine and its ...
ii. 12o 13.
J. G. po Vo by
Nai, Physical Properties of Crystals [Russian translation]~ Mir, Moscow (1965) o Korn and T~ Korn~ Handbook of Mathematics [Russian translation], Nauka, Moscow (1978), 450. Do Tkachev et alo, "Detection of the chemical activity of the noble gases in silicon the luminescence method~" Dok!. Akad. Nauk BSSR, 23, 315-318 (1979),
TRIPLET--TRIPLET ABSORPTION SPECTRA OF PHTHALOCYANINE AND ITS METAL COMPLEXES UDC 535.34
V. E. Pyatosin and M. P. Tsvirko
Phthalocyanine and its metal complexes have a number of unique oPtical and physicochemical properties, which explain the wide use of these compounds in modern science and technology. Thus, using phthalocyanine and its complexes with aluminum and vanadium passive Q-switching of a ruby laser has been achieved [i], and using a solution of AiCl-phthalocyanine the effect of the generation of coherent radiation by organic compounds was first observed [2]. Subsequently, using derivatives of phthalocyanine, highly effective and stable passive Qswitches for neodymium [3] and iodine [4] lasers were developed~ Recently, using solutions of anumber of metal-phthalocyanines, effective lasing was obtained in the red region of the spectrum using the emission of a nitrogen laser for pumping [5]. The particular features of metal-phthalocyanines in quantum electronics are determined by the ratio of the singlet--singlet and triplet--triplet absorption cross section, and also by the values of the radiational and radiationless transition probabilities from excited states~ Nevertheless, only very limited information is available in the literature on the absorption spectra from excited states ofphthalocyanines. In the majority of papers it is merely stated that induced absorption or luminescence of the materials occurs (see [6] and the references given there)~ Quantitative spectra of triplet--triplet absorption have been determined using pulsed lamp photolysis for compounds having a fairly long lifetime of the triplet state (~10 -4 sec) in oxygen-free solutions, phthalocyanine[7] and its complexes with Mg and Zn [8]~ Due to the intense fluorescence of the phthalocyanines measurements were not made in the most interesting region (>640 nm). In this paper we present the results of an investigation of the spectra and kinetics of~ triplet--triplet absorption of the free base of phthalocyanine and its complexes with aluminum~ gallium, and vanadium in oxygen-free solutions at room temperature using laser-photolysis equipment. To excite the Phthalocyanines we used the first harmonic (694 nm) and the second harmonic (347 nm) of a Q-switched ruby laser with energies of up to 0.6 J and 0~05 J, respectively. We used as the probing source a DKSSh-150 xenon lamp, through which a constant current of 3 A passed, and at the required moment a in synchronism with the laser pulse, a line was also discharged, generating a rectangular pulse about 75 ~sec long. The recording system consisted of a Spex-1870 diffraction monochromator (with an inverse linear dispersion of 16 ~/mm), an FEU-84 photomultiplier, and an $8-7A storage oscilloscope with a passband of 20 MHz. To record the weak induced absorption we employed a circuit for compensating the electric signal from the probing pulse by means of a constant potential equal to the pulse amplitude, applied to the differential input of the oscilloscopes~ All the measurements were made in cuvettes i0 mm longo The following were used as solvents: for the free base of phthalocyanine~-- ~-chlornaphthalene, for GaCI and VO-phthalocyanines, chlorbenzene, and for AlOH-phthalocyanine, orthodichlorbenzene~ The chlorbenzene and orthodichiorbenzene were purified using the method described in [9], and the ~-chlornaphthalene was subjected to vacuum distillation. The purity of the phthalocyanines was checked from the absorption and fluorescence spectra. The concentrations of the materials investigated was 0.3-1.10 -~ mole/liter. The triplet--triplet absorption spectra were measured both for excitation with radiation of wavelength 694 nm in the region of the long-wave absorption band, and at 347 ~ , which
1980o
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 33, No. 2, pp. 320-325, August, Original article submitted September 20, 1979o
0021-9037/80/3302-0869507.50
9 1981 Plenum Publishing Corporation
869
falls in the ultraviolet absorption band of metal-phthalocyanines, and were identical, Further, in the latter case, while measuring the triplet--triplet absorption spectrum we observed dissociation of the materials. Thus, for GaCl-phthalocyanine inchlorbenzene the action of one hundred pulses at a wavelength of 347 nm led to 10% dissociation. Nevertheless, the use of 347 nm for excitation enabled us to eliminate the effect of scattered light when measurements were made in the region of the long-wave absorption band. The tripiet~triplet absorption spectrum for 100% conversion into the T1-state is defined as DT(~) = Ds(%) + AD(~), where D T is the optical density of T~ § T n absorption, D s is the optical density of So + S n absorption, and AD is the change in the optical density of the solution due to the action of the pumping pulse. The compounds investigated differ considerably in the lifetimes of the S~-state ands'the quantum yield of intercombination conversion into the T~-state. Hence, to ensure complete conversion ofthe molecules into the triplet state for materials having comparatively long lifetimes in the S:-state (6-7 nsec), and low values of the quantum yield of interconversion (30-40%) of phthalocyanine andAlOH-phthalocya- ~ nine, the excitation pulse length was 60 nsec, whereas for materials with high values of the quantum yield of intercombination conversion of VO and GaCI phthalocyanines it was 20 nsec. The length of the exciting pulses was varied by changing the density of the passive Q-switch of the laser. Note that when using pulses of 18 nsec duration to pump phthalocyanine andAlOH phthalocyanine into the TI state not more than 70% and 50% of the molecules, respectively, could be transferred even for pumping energies of ~0.5 J due to the considerable build-up of molecules in the S~-state. Reversible changes are observed due to the action of the laser emission at a wavelength of both 694 nm and 347 nm in the absorption spectra of phthalocyanine and its complexes with aluminum, gallium, and vanadium; The initial absorption bands are cleared and a new absorption occurs in the whole visible region of the spectrum. In the near infrared region of the spectrum (>730 nm) for all the compounds investigated no induced absorption was observed. The durations of the lightening processes and the occurrence of the new absorption coincide, within the limits of experimental error, and are 800, 550, 375, and 35 nsec for the free phthalocyanine base and its complexes with aluminum, gallium, and vanadium respectively. Degassing of the solutions leads to an increase in T T for phthalocyanine and its complexes with gallium and aluminum, but has no effect on T T for VO-phthalocyanine. The amplitudes of the brightening signals and the induced absorpti6n depend in the same way on the energy of the exciting pulse. At a certain pumping energy this dependence reaches a plateau, which confirms the practically complete conversion of the molecules into the lower triplet state. The observed residual absorption in the region of the initial bands and the new induced absorption, as follows from the data obtained, is due to T: ~ T n transitions. A confirmation of the 100% conversion of the molecules into the lower triplet state is the practically complete brightening of the long-wave absorption band. The residual absorption has a value of less than 4% of the initial absorption. It should also be noted that from the structure of the triplet-triplet spectrum when 100% conversion into the triplet state in the maxima of the most intense initial absorption bands does not occur, an overshoot, which repeats the contour of the So + S n absorption bands, is observed [i0]. This structure is not observed in the calculated triplet--triplet absorption spectra. The calculated triplet--triplet absorption spectra are shown in Fig, i. The table shows the absorptions of the main maxima and the extinction coefficients of the triplet--triplet and singlet--singlet absorptions. The triplet--tripletabsorpti0n spectrum of the free phthalocyanine base obtained agrees in the 400-600-nm range with the spectrum obtained by lamp photolysis [7]. In the longer wave region we did not observe the maximum for 635 nm, which was observed in [7]. The triplet--triplet absorption spectra of AIOH, GaCI, and VO phthalocyanines are similar to the spectra of the triplet--triplet absorption of the free phthalocyanine base, and also Mg and Znphthalocyanines [8]. The extinction coefficients at the maximum of the triplet--triplet absorption are about 3.4-10 ~ mole-~-liter.cm -~, Despite the diffusion nature of the triplet--triplet absorption, we observed the effect of the nature of the metal on the position of the maximum of the triplet--triplet absorption. As in the case of porphyrines [8]~ the replacement of a metal atom at the center of the phthalocyanine ring, which leads to a short-wave displacement of the 0-0 band of the So ~ S~ transition, also leads to a shortwave displacement of the main maximum of the triplet--triplet absorption. Thus, for Mg and Zn phthalocyanines, whichhave a maximum of the So *$I absorption band in the region of 670-675 nm, the triplet--triplet absorption maximum is situated at 470 nm, whereas in AIOH, GaCI and VO phthalocyanines the corresponding bands are situated at 695 and 490 rim. It is possible that
870
1,5--
~o-
~5
500
~00
500
17
1
goa
-'
go
'
67o
'
7oo
Z,~m
Fig. i. Singlet--singlet spectrum (i) and triplet--triplet absorption spectrum (2) of phthalocyanine in G-chlornaphthalene (a),AlOH-phthalocyanine in o-dichlorbenzene (b), GaCl-phthalocyanine (c) and VO-phthalocyanine (d) in chlorbenzeneo TABLE i. Characteristics of the Singlet--Singlet and Triplet-Triplet Absorption Spectra
Material
9I
SoIvent
max gmax X '1 max s , 1~-', mo lelki~ TT' nm l: cm-i I
max
-STT X s 0~,
I~*
~r,msec
mole 9l 9 cm -i
I
- e tiChlomaphthaleneI Phth~IocYamn GaC1 phthalocyanine |Chlorbenzene VO-iphtha locyanine IChl0rbenzene A10~t-phtha loeyaninelo'Dichlorbenzene
699 690 692 694
1,6 2,4 2, i 1,8
I 480 I 490 ' 490 495
3,2 3.7 314 3,6
47 42 2s 27
800 370 35
540
i
*~ = gSS/eTT at the maximum of the long-wave absorption band, this feature has a fairly general character, and when the nature of the metal or the composition of the solvent which is responsible for the displacement of the So + S: absorption band is changed, the spectrum of the triplet--triplet absorption is similarly displaced. This is confirmed by data from investigations of phthalocyanines in systems which give a strong longwave displacement of the So § $I absorption band. Thus, for bromine phthalocyanine in eutectic, which has a long-wave absorption band maxlmum at 1022 nm, a fairly strong residual absorption was observed at the wavelength of a neodymium laser [3], In the most interesting region of the long-wave absorption band, from the point of view of quantum electronics, all the metal complexes investigated have cpproximately the same values of extinction coefficients of triplet--triplet absorption STT = 7,103 mole-:.liter,cm -I,
g7i
In a number of papers, based on measurements of the transmittance of solutions of metal phthalocyanines as a function of the power density of the incident radiation, considerably higher values were obtained for the extinction coefficients of triplet-triplet absorption at the wavelength of the ruby laser. These results are obviously too high due to the difficulty of controlling a number of additional effects in addition to absorption from the lower triplet state: thermooptical distortions of the medium, induced scattering, and So + S absorptiono n LITERATURE CITED i. 2. 3.
4. 5. 6. 7. 8.
9. I0o
872
P. P. Sorokin~ J. J. Luzzu, J. R. Lankard, and C. D.Pettit, "Ruby laser Q-switching elements using phthalocyanine molecules in solution," IBM J. Res. Dev., 8, 182-184 (1964). P. P. Sorokin and J. R. Lankard, "Stimulated emission observed from an organic dyechloroaluminum phthalocyanine, ~' IBM J. Res. Dev., i0, No. 2, 162-163 (1966). O. L. Lebedev, Yu. M. Gryaznov, and A. A. Chastov, "Brightening of phthalocyanine solutions by the action of neodymium laser emission," Opt. Spektrosk., 2_44, No. 2, 300-301 (1968). M. G.Gal'pern et al., "A brightening filter for an iodine laser at a wavelength of 1.315 nm," Kvantovaya Elektron., ~, No. ii, 2531-2532 (1975), Ro Kugel et al., "Laser properties of some phthalocyanines," Opt. Commun., 23, 189 (1977), V. A. Pilipovich and A~ A. Kovalev, Lasers with Brightening Filters [in Russian], Nauka i Tekhnika, Minsk (1975), pp. 5-98. J. C. Villar and L. Lindquist, "Spectral absorption and decay kinetics of the triplet state of phthalocyanine in solution," Compt. Rend. Sci., B264 , 1807-1810 (1973), M. P. Tsvirko, V. V. Sapunov, and K. N. Solov'ev, "Triplet--triplet absorption and phosphorence of metal porphyrines in liquid solutions," Opt. Spektrosk,, 34, 1094-1100 (1973), Ao Vaisberger~ E. Proskader, D. Ruddik, and E. Gupa, Organic Solvents [Russian translation], IL, Moscow (1958), p. 387. H. Linschitz and K. Sarkanen, "The absorption spectra and decay kinetics of the metastable states of chlorophyll A and B," J. Am. Chem~ Soc., 8~0, 4826-4832 (1958),
