Ketskeméty, István

Szalay, László

Várkonyi, Zoltán

English

Ketskeméty István

Szalay László

Várkonyi Zoltán

University of Szeged

EFFECT OF SOLVENT ON THE ABSORPTION AND FLUORESCENCE SPECTRA OF ALCOHOLIC SOLUTIONS OF TRYPAFLAVINE By I. K E T S K E M É T Y , L. S Z A L A Y and Z . V Á R K O N Y I Inst i tute of Experimental Physics, József Attila University, Szeged (Received 10, January, 1965) The validity of STEPANOv-relation concerning the connection of absorpt ion and emission' spectra has been proved fo r solutions of trypaflavine in different alcohols of the homologous-1. An equation connecting the absorption spectrum e(v) and the emission energy spectrum fe(v) has been derived by STEPANOV [1] = dv3exp(-hv/kT), (1> where v and T denote the frequency and the temperature of the solution, respecti-vely; h and k are PLANCK'S and BOLTZMANN'S constants, d is a constant independent of frequency. • KETSKEMETY and co-workers [2] have pointed out, that instead o f eq. (1) a modified form of it can be considered more reliable: • ^ l = Dri*(\)n2(v)v3exp(~hv/kT), (2> g(v) where t]*(v) and M(V) denote the relative yield of fluorescence and the refractive index of,the solution, respectively. In case of r\* (v) == const and n(v) = const (practi-cally in a smaller spectral region) eq. (2) is identical with eq. (1). Eq. (1) may be rewritten in terms of the wavelength, X: F(/.) = log/(A) + 4 log A — log s(A) = = —hcl2,30kTX + const; f(X) is the emission quantum spectrum as a function o f the wavelength / . If eq. (1) is valid F(X) is a linear function of X and the slope o f the straight is determined by the temperature T of the solution. The temperature T* obtained f rom the slope of the straight was found to be T* is most cases. STEPANOV [3], ALENTSEV [4], ALENTSEV a n d PAHOMITCHEVA [5], KRAVTSOV a n d RUBINOV [6], KETSKEMETY a n d c o - w o r k e r s [2], HEVESI a n d KOZMA [7], R H A Z A -NOVA a n d c o - w o r k e r s [8], f u r t h e r BORISSEVICH a n d GRUZINSKII [9] a n d GRUZINSKII and BORISSEVICH [10] carried out experiments in order to control the validity o f STEPANOV'S equation in luminescent solid, liquid and vapour systems. In all the investigated systems eq. (1) — in a given spectral region where >f (v) and n(y) are approximatly constant — has been found to be valid, and temperatures of 7"* ^ T were obtained. 1 6 I. KETSKEMÉTY, tl. SZALAY AND Z . VÂRKONYI There is no doubt temperatures of T* >T may be derived from the slope of the STEPANOV'S straights in many cases, however,-the nature of this higher tempera-ture is not clear enough. Though the excess of the exciting energy — the source -of the increase of temperature — could easily be degraded in condensed (solid and liquid) systems on account of the strong interaction of solute and solvent, T* was found to be higher than T even in many of these systems. In order to clear up the nature of this interaction the effect exerted by the solvent on the same solute ought to be known. The aim of the present paper is to contribute to a better under-s tanding of the phenomena in liquid systems. In order to explain some phenomena found in the polarization of fluorescence -of solutions, JABLONSKI [11] suggested a mechanism for degradation of the excess of exciting energy. According to this mechanism a part of the excess-energy is •converted into the energy of elastic waves by an "initial shock" and the other part i s converted into heat ("slow effect") in the neighbourhood of the excited particles Mmn) — — Fig. 1 t h u s causing a depolarization of fluorescence. JABLONSKI'S investigations seem to fu rn i sh further reasons to carry out experiments referring to the problem of T*. 2. Trypaflavine purified by repeated crystallization was dissolved in different monohydric alcohols (see Table 1) of spectroscopic purity1 in a concentration of •cM — 3 -10" 4 mole/1. The absorption and emission spectra have been determined 1 Au thors are indebted to dr . J. Hires for making available some purified solvents. EFFECT OF SOLVENT ON THE ABSORPTION AND FLUORESCENCE SPECTRA 17 by means of a spectrophotometer (Optica Milano CF4) at a temperature of T = 293 ± 2° K. Fig. 1 exhibits two examples of these spectra, the main characte-ristics of absorption and emission for all solutions investigated are shown in Table I ( W L = 2,3026-cM-8(;.)max). Table I 1 2 3 4 5 6 Solvent absorpt ion emission ''•max ( > m ) T* obtained f rom spectra corrected to ''-max ( " I f ) k W m a x reabsorpt ion secondary fluor. methanol 457,6 14,40 496,9 352,3 324,0 ethanol 462,0 19,35 493,8 356,8 326,6 1-propanol 462,8 15,05 495,0 375,0 336,7 2-propanol 463,0 12,99 495,4 380,1 338,1 1-butanol 463,2 14,14 495,4 390,5 345,2 2-pentanol 463,8 13,62 498,6 445,9 373,9 The excitation was carried out at a wavelength of 436 mjj. with a high pressure mercury lamp. The directions of excitation and observation were approximately parallel. The layer thickness of solutions was / = 0,1 cm. The spectral influence of reabsorption (a) of primary fluorescence and the spectral influence of secondary fluorescence (b) on emission spectra were eliminated according to a method given by BUDO and KETSKEMETY [12]. Both the emission spectra corrected taking into account of effect (a) and those corrected taking the effect (b) into consideration were used for the determination of T* in all solutions; the results are shown in Table 1. Some examples of the fulfilment of eq. (1) is to be seen in Fig. 2. (The straight lines were constructed by the method of "least squares".) As for the experimental results, the following remarks should be made. The elimination of influence (b) (of secondary fluorescence) seems to be very important, because the temperatures T* obtained from the emission spectra corrected taking into account reabsorption (/. e. influence (a)) only are much greater than those obtained f rom spectra corrected taking the effect (b) into consideration (see Table I, columns 5 and 6)2. The temperature T* increases when we go over to a higher alcohol. This phenomenon is similar to that found by HEVESI and KOZMA [7] in case of fluorescein dissolved in glycerol-water mixtures. In both systems T* increa-ses with the viscosity. 3. A rather rough model — as an alternative of that given in [13] — can be constructed for an illustration of the processes taking place after excitation — provided there exists a microregion of a temperature T* > T. The excess of the 2 Ketskemety and co-workers give a value of T* =321° K for an ethanolic solution of try-paflavine in a good accordance with the present value of 326,6° K obtained f rom an emission spectrum corrected to secondary fluorescence. According to Alentsev and Pahomitcheva [4] effect (b) should cause an increase of T*. As a matter of fact, the spectral influence of secondary fluores-cence depends on the conditions of excitation and observation and on the exciting wavelength as well and may change (either increase or decrease) the value T*. 18 I . KETSKEMETY, L. SZALAY AND Z. VARKONY1 exciting energy is converted into heat during the process of excitation and is distri-buted in a sphere of radius r' and it causes a local temperature of > T. The temperature difference may be estimated as follows: T* T 3k'h(va-ve max) I o— t — — , ( J> 4nr 3 QC where k' = 2,39-10~8 cal/erg, h(va — ve max) = 5,4-10"1 3 erg (the excess of the excit-ing energy estimated f rom the frequencies of excitation and emission maximum) , A Imp) — — Fig. 2 qc^0,5 (q and c are the density in g/cm3 and the specific heat in cal/g grad of the alcohols, respectively. On assuming a value of r' = 3 A , T^ — T ^ 250°. M a k i n g use of the data in Tab. 1 eq. (3) yields a series of values of the order of 5 A fo r r (5,8 A in methanol and 4,3 A in 2-pentanol). This seems to be a reliable value because the avarage distance of the neigbouring excited solute particles is obviously much greater. * * * Authors are indebted to I. BECK and S. CSAKI for their valuable help in carry-ing out the experiments and calculations. EFFECT OF SOLVENT ON THE ABSORPTION AND FLUORESCENCE SPECTRA 19 References [1] Stepanov, B. 1.: D A N URSS 112, 839 (1957). [2] Ketskeméty, /., J. Dombi, R. Horvai: Ann. Phys. 7, 342 (1961); Acta Phys. Hung. 14,165 (1962). [3] Stepanov, B. / . : I A N URSS 22, 1367 (1958). [4] Alentsev, M. N.: Opt. i Spektr. 4, 690 (1958). [5] Alentsev, M. N., L. A. Pahomitcheva: I A N URSS 22, 1377 (1958.); 24, 734 (1960). [6] Kravtsov, L. A., A. N. Rubinov: Opt. i Spektr. 12, 636 (1962). [7] Hevesi, J., L. Kozma: Acta Phys. et Chem. Szeged 8, 103 (1962). [8] Rhazanova, E. F., M. S. Fadeeva, T. S. Pavlina: I A N URSS 24, 769 (1961). [9] Borissevich, N. A., V. V. Gruzinskii: Opt. i Spektr. 14, 39 (1963). [10] Gruzinskii, V. V., N. A. Borissevich: Opt. i Spektr. 15, 457 (1963). [11] Jabtoúski, A.: Acta Phys. Polon. 26, 427 (1964). [12] Budó, A., I. Ketskeméty: J. Chem. Phys. 25, 596 (1956); Acta Phys. Hung. 7, 207 (1957). [13] Kozma, L., L. Szalay, J. Hevesi: Acta Phys. et Chem. Szeged 10, 67 (1964). В Л И Я Н И Е Р А С Т В О Р И Т Е Л Я Н А С П Е К Т Р А Х П О Г Л О Щ Е Н И Я И Л Ю М И Н Е С Ц Е Н -Ц И И С П И Р О В Ы Х Р А С Т В О Р О В Т Р И П А Ф Л А В И Н А И. Кечкемети, Л. Салаи, 3. Варкони В случае разных спритовых растворов трипафлавина исследовалось выполнение соотношение Степанова, описывающие связь между спектрами поглощения и люминес-ценции. 2* 

Effect of solvent on the absorption and fluorescence spectra of alcoholic solutions of trypaflavine

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Effect of solvent on the absorption and fluorescence spectra of alcoholic solutions of trypaflavine

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