452
J. Phys. Chem. 1980, 84, 452-456
Table IX. The theoretical ratios were calculated from the agement during this work. determinants of the G matrix, and the experimental values were evaluated from the Raman frequencies by employing References a n d Notes the calculated values for the CNB linear bending. The B. Swanson and D. F. Shriver, Inorg. Chem., 9, 1406 (1970). agreement seems to be reasonably good. D. F. Shriver and B. Swanson, Inorg. Chem., 10, 1354 (1971). V. Devarajan and S.J. Cyvin, Z. Naturforsch. A , 26, 1346 (1971). Comparison of stretching frequencies and valence force H. I.Schiesinger and A. B. Burg, Chem. Rev., 31, 1 (1941). constants of the C=N, C-C, and N-B bonds for acetoH. J. Emeleus and K. Wade, J . Chem. Soc., 2614 (1960). nitrile-BX3 adducts is given in Table X. Both the C=N I.Shapiro, H. G. Weiss, M. Schmich, S.Skolnik, and G. B. L. Smith, J . Am. Chem. Soc., 74, 901 (1952). stretching frequency and the force constant for the borane R. Amster and R. C. Taylor, Spectrochim. Acta, 20, 1487 (1964). adduct are larger than those for free acetonitrile. The R. N. Jones and A. Nadeau, Spectrochim. Acta, 20, 1175 (1964). increase in the C e N stretching frequency and in the force E. B. Wilson, Jr., J. C. Decius, and C. Cross, "Molecular Vibrations", constant upon adduct formation have been d i s c u s ~ e d . ' ~ ~ J ~ J ~ McGraw-Hill, New York, 1955. B. Swanson, D. F. Shriver, and J. A . Ibers, Inorg. Chem., 6, 2182 The C-C stretching frequency of the borane adduct is (1969). larger than that of free acetonitrile, nevertheless, the C-C P. Cassoux, R. L. Kuczkowski, R. S.Bryan, and R. C. Taylor, Inorg. force constant is smaller. The increase in the C-C Chem., 14, 126 (1975). C. C. Costain, J . Chem. Phys., 29,864 (1958). stretching frequency should be interpreted to be due to J. Overend and J. R. Schere, J. Chem. Phys., 32, 1289 (1960). kinematic coupling with the N-B stretching vibration J. H. Schachtschneider and R. G. Snyder, Spectrochim. Acta, 19, (Tables 111-VI, PED), as in case of the boron trihalide 117 (1963). F. Watari, Bull. Chem. SOC.Jpn., 50, 1287 (1977). adducts.',2 K. Nakamoto, "Infrared Spectra of Inorganic and Coordination Heats of formation of the solid acetonitrile-BX, adduct Compounds", 2nd ed, Wiley, New York, 1970. from their gaseous constituents have been reported to be E. B. Wilson, Jr., J . Chem. Phys., 9, 76 (1941). K. F. Purcell and R. S.Drago, J. Am. Chem. Soc., 88, 919 (1966); 164.8,20141.4,21110.8,21and 106.2 kJ/mo15 for CH,CN.BK. F. Purcell, ibid., 89, 6139 (1967). Br,, .BCl,, .BF,, and .BH3, respectively. The order of J. Yarwood, Ed., "Spectroscopy and Structure of Molecular adduct stabilities deduced from the N-B force constants Complexes", Plenum, New York, 1973. J. M. Miller and M. Onyszchuk, Can. J . Chem., 43, 1877 (1965). in Table X is consistent with the order of the heats of A. W. Laubengayer and D. B. Sears, J . Am. Chem. Soc., 67, 164 formation, though it has been reported that the N-B bond (1945). strength is approximately the same for the boron triThough J. L. Duncan has reported the CN and CC force constants as18.11 X 102and5.16X 102Nm-'(Spectrochim.Acta,20,1197 chloride and tribromide adductse2
Acknowledgment. The author expresses his sincere gratitude to Professor K. Aida for his continued encour-
(1964)), the force constants used here were determined from liquid Raman data on CH,CN and CD,CN by using a similar force field to that employed here and are almost the same as those of Swanson and Shriver.'
Polarized Absorption Spectra of Aromatic Radicals in Stretched Polymer Film. 3.'12 Radical Ions of Acridine and Phenazine Ken'ichi Sekiguchi, Hiroshi Hiratsuka," Yoshie Tanizaki,+ and Yoshihiko Hatano Department of Chemistty, Tokyo Institute of Technology, Ohokayama, Meguro-ku, Tokyo 152, Japan (Received July 20, 1979)
Radical anions and .cations of acridine and phenazine have been prepared in polymer film by y-ray irradiation at 77 K. For the preparation of radical anions the sample was incorporated into polyethylene film by secbutylamine, while for radical cations poly(viny1 chloride) film and sec-butyl chloride were used. Polarized absorption spectra of these radical ions have been measured in stretched polymer film and analyzed qualitatively in terms of MO calculations.
Introduction The electronic spectra of aromatic N-heterocyclic radicals have been studied by various means such as photo~ h e m i c a lradiation ,~ ~ h e m i c a land , ~ electrochemical technique~ and ~ a conventional alkali metal reduction method.6 There have been, however, few reports on polarization measurement of their spectra. In the first paper of this series,' we showed that the acridine semiquinone radical was obtained by y-ray irradiation of acridine dissolved in poly(viny1 alcohol) (PVA) film with aid of the solvent methanol. Polarized absorption spectra of the radical were determined by making use of t The Department of Materials Science and Technology, Technological University of Nagaoka, Nagaoka, Niigata 949-54, Japan.
0022-3654/80/2084-0452$0 1.OO/O
stretched PVA film. Recently, an extension of this stretched polymer film technique to aromatic hydrocarbon radical ions has been carried out by using suitable polymer films and solvents.2 It has been shown that PVA-secbutylamine system and poly(viny1 chloride)-sec-butyl chloride system are available for the preparation of the radical anion and cation, respectively. In this paper, we apply these systems to the preparation of radical ions of aromatic N-heterocyclic compounds and measure the polarized absorption spectra of these radical ions. Experimental Section Acridine (Aldrich Chemical Co.) and phenazine (Guaranteed Reagent, Tokyo Kasei Co., Ltd) were used without 0 1980 American
Chemical Society
Radical Ions of Acridine and Phenazine
25
20
15 Wave number(103cm-')
The Journal of Physical Chemistry, Vol. 84, No. 4, 1980 453
20
Wave number 15 (103cK') 10
of acridine (a) and phenazine (b) in
Figure 1. Absoipption spectra of acridine (a) and phenazine (b) in y-irradiated PE films.
Figure 2. Absorption spectra y-irradiated PVC films.
further purification. As the solvents, Guaranteed Reagent see-butylamine (BuA), see-butyl chloride (BuCI), and carbon tetrachloride (CClJ were used without further purification. Poly(viny1chloride) (PVC) and polyethylene (PE) films uscid were commercially available. Poly(viny1 alcohol) film was prepared as in the same way as before.2 The sample films were made by incorporating the parent molecules into polymer films with aid of suitable solvents. The radical ions were prepared by irradiation with @Xo y rays of the sample films a t 77 K for 2.5 h with a dose rate of 1.08 X lo6 rd/h. The absorption spectrum was measured in the region of (12-25) X IO3 cm-' with a JASCO SS-50 type spectrophotometer modified to a double-beam system and equipped with a Rochon polarizer. The absorption spectrum below 18 X lo3 cm-l was measured with a Cary 14 spectrophotometer. Polarization measurement was carried out for the stretched sample film. The dichroic ratio, Rd, is defined as All/A,, where All and A , denote, respectively, absorbances when the electric vectors of the incident polarized light are parallel (11) and perpendicular (1) to the stretching direction of the film. MO calculations on acridine and phenazine radical ions were carried out by use of Roothaan's restricted Hartree-Fock open shell method in the a-electron approxim a t i ~ n .Configuratnon ~ interactions were limited to all singly excited and ground configurations. One- and twocenter electron repu1s;ion integrals were estimated by the Pariser--Parr The ionization potentials (I& the electron affinities (233,and the resonance integrals (P,) for carbon and aza-nitrogen atoms were taken as Ip(C) = 11.22 eV, E,(@) = 0.62 eV, Ip(N) = 14.51 eV, E,(N) = 1.20 eV, PCC = -2.318 eV, and BcN = -2.38 eV. All the bond lengths were set equal to 1.395 A.
ever, resembles that of the acridine semiquinone radical (acridine C radical) rather than the acridine radical anion. This fact suggests that, even in a PVA-BuA system, proton addition to the anjon occurs in a way similar to that in the PVA-methanol system.' In order to exclude proton addition, we examined a PE-BuA system. Figure l a shows the absorption spectrum of the species produced upon y irradiation of acridine in a PE-BuA system. Since this spectrum is similar to the absorption spectrum of the acridine radical anion which was obtained by y irradiation of a 2-methyltetrahydrofuran (MTHF) matrix of acridine at 77 K,4b the absorption spectrum in Figure l a is attributed to the acridine radical anion. It is concluded that a PE-BuA system is suitable for the preparation of the radical anion of acridine. Figure l b shows the absorption spectrum of the species produced upon y irradiation of phenazine in a PE-BIuA system. The spectrum resembles that of the phenazine radical anion prepared by the electrolysis technique.[' I t also resembles that of the phenazine radical anion prepared except that the latter in MTHF glass by y irradiati~n,~" does not show the weak band a t about 15 X lo3 crn-l. Thus, the spectrum in Figure l b is due to the phenazine radical anion. Preparation of radical cations has also been examined. The samples were incorporated into PVC film according to the method for aromatic hydrocarbons described in a previous paper.2 Figure 2a shows the absorption spectrum of the species produced upon y irradiation of acridine in a PVC-(BuCI+CC1,) system, and the spectrum below 13 X lo3 cm-' (indicated by a broken line) was measured by use of a PbS phototube. The spectrum bears a resemblance to that of the acridine redical cation prepared in BuCl glass by y i r r a d i a t i ~ n .Therefore, ~~ the spectrum of Figure 2a is ascribed to the acridine radical cation. Figure 2b shows the absorption spectrum of the species produced upon y irradiation of phenazine in a PVC(BuCl-tCClJ system. The spectrum below 13 X lo3 cm-l (indicated by a broken line) was measured by use of a I'bS phototube. I n the spectrum absorption peaks are found at 9 X IO3 and 21 X lo3 cm-l and shoulders appear at 15.5-16.5 X lo3 and (17-18) X lo3 cm-'. Their positions
Results and Discussion Preparation of Radical Ions. The method for the preparation of aromatic hydrocarbon radical ions has been used for the preparation of acridine radical anion: acridine was incorporaited into PVA film with the aid of BuA (PVA-EuA system) and the sample film was irradiated by y-rays a t 77 M. The resulting absorption spectrum, how-
454
The Journal of Physical Chemistty, Vol. 84, No. 4, 1980
a -
1.01
U
;0
n
4
.......... f0J-
'
Z
(b)
Y
,z .10
,Y
Sekiguchi et ai. TABLE I: Calculated and Experimental Results for Acridine Radical Ions transitn energy, l o 3 cm-' polarizatna oscillator strength calcd obsd calcd obsd (calcd) Radical Anionb 1 15.84 12-14 Y d 0.0280 Y Y 0.0931 2 16.89 15.6 3 17.83 16.7 Z Z 0.0235 4 24.27 25 z z 0.0018 5 25.80 z 0.1015 Y 0.0000 6 26.49 Radical CationC 1 11.07 Y 0.0176 11 Y Y 0.1153 2 12.62 3 17.45 15-20 Z Z 0.0072 21 Z Z 0.0176 4 22.77 z 0.1128 5 25.41 a Y and Z are the molecular long and short axes, respectively. In a y-irradiated PE-BuA system. In a 7 - h a diated PVC-(BuCltCCl,) system. See text.
Rd13t
..... 1 .0 ..........................................
;:. .............. ..._..' ,
I
(a)
.. ........... \i'.., ..,.
I
i
.'.".,
f0,-
(b)
2 ,Z
Z.5 I
,Y
f 0.1
( b)
e
30
?? 25
20
p
f
15
10
Wave number (103crii')
Figure 5. Polarized absorption spectra (a) and calculated spectrum (b) of the phenazine radical anion in y-irradiated PE film. Open circles (f) represent forbidden transitions. 2 polarized because of the small Rd value. The calculated
result shows, however, Y polarization for the first transition. This discrepancy could not be explained at the present stage. The assignment of the spectrum of acridine radical anion is summarized in Table I. Figure 4a shows the polarized absorption spectra of the acridine radical cation in stretched PVC film. Though the variation of Rd curve is rather small in the whole region, it is found that the R d value below 13 X lo3 cm-' is greater than that in the higher wave number region. This Rd behavior is analyzed by reference to the result of MO calculations (see Figure 4b). The strong band at 11 X lo3 cm-' in Figure 2a, which is not shown in Figure 4a owing to the limitation of the spectrophotometer, is expected to be the Y-polarized band. The band in (15-20) X lo3 cm-l region and the peak a t 21 X lo3 cm-' are polarized along the 2 axis because of its small Rd value. The assignment of the bands is tabulated in Table I. Phenazine. The polarized absorption spectra of the phenazine radical anion in stretched PE film are shown in Figure 5a. The intense band a t (17-20) X lo3 cm-l is Y polarized because of its great Rd value and is assigned to the third transition at 19 x lo3 cm-' in Figure 5b. The absorption in the region of (22-25) X lo3 cm-l is 2 polarized because of its small Rd value and seems to be ascribed to the fourth and fifth transitions. Since the Rd curve below 17 X lo3 cm-' is depressed abruptly a t 16.5 x lo3 cm-', the 16.5 X lo3 cm-l peak should be distinguished from the band below 16 X lo3 cm-l and is assigned
The Journal of Physical Chemistty, Vol. 84, No. 4, 1980 455
Radical Ions of Acridine and Phenazine TABLE 11: Calculated and Experimental Results for Phenazine Radical Ions ~ - _ _ _ _ oscillator transitn 'energy, l o 3 cm-' polarizatna strength --calcd obsd calcd obsd (calcd)
-
TABLE 111: Characteristic Absorption Bands in the Visible Region of Anthracene, Acridine, and Phenazine Radical Ions
-
Radical Anionb 1
16.5 14-16 17-20
17.88 18.74 18.92
2 3
7
Z
f Y
Z Y Y
Y
29.61
0.0286 0.0860
0.1354
Radical Cati6nc 1
f
8.25 9.44 15.BO 23.1 8 24.35
2 3 4 5
Y 16-17
Z f
z
0.1058 2
0.0042 0.1307
anthracened acridine phenazine
Y polarizeda
Z polarizeda
A E , l~o 3 cm-' RIC A E , b l o 3 cm-' Radical Anion 13.7 (11) 1.0 15.5 (111) 15.6 (11) 1.0 16.7 (111) 1 7 - 2 0 (111) 1.0 16.5 (11)
RI" 0.6 0.9 0.5
Radical Cation anthracened 13.6 (11) 1.0 16.0 (111) O.f! acridine 11 1.0 1 5 - 2 0 0.41 phenazine 16-17 a I1 and 111 correspond t o the second and the third abA E denotes the transition sorption band, respectively. RI denotes relative intensit17 energy of observed band. of the absorption maximum and is estimated by the Y Reference 2. polarized band being taken as unity.
a Y and 2 are the molecular long and short axes, respectIn a 7ively. f means, that the transition is forbidden. In a 7-irradiated PVCirradiated PE-BuA system. (BuCl+ CCl,) system.
I
""I 10
0O L
U -)?I * LQ7 67
py&
Figure 7. Schematic representatlon of some MO's of the anthracene radical anion. I1 and I11 correspond to the second and the third
transitions, respectively.
Figure 6. Polarized absorption spectra (a)and calculated spectrum phenazine radical cation in y-irradiated PVC film.
(b) of
to the second band. The intensity of this band is greater than that of the first band ((14-16) X 103cm-l). Therefore, the second band can be ascribed to the first transition (2 polarized). As a result the first band is attributed to the second (forbidden) transition. By reference to the calculation of Ezurni et al. (Longuet-Higgins-Pople type SCF MO-CI cal~ulation),~ the order of these two transitions is reversed. Our experimental result is in good agreement with their results. The assignment of the bands is shown in Table 11. The polarized absorption spectra of the phenazine radical cation are also determined as shown in Figure 6a. The variation of the Rd curve is rather small in the whole region, but it is found that the shoulder a t (16-17) X lo3 cm-l is 2 polarized because of its small Rd value. The calculated result for the phenazine radical cation is shown in Figure 6b. The assiginment of the bands is tabulated in Table 11. Shift of the Visible Bands of Anthracene, Acridine, and Phenazine. According to Figure 1, the visible bands of phenazine seem to be shifted to higher energies compared with those of acridine. The blue shifts of the bands of these anions lhave been studied by Ezumi et al.5 They recognized the blue shift of these compounds from band positions and shape, and explained the shift by taking into account the clhange in the orbital energies upon N-atom replacement. Now, in connection with the result obtained for the anthracene radical anion,2 this blue shift can be investigated in more detail by dichroism analysis. Table
I11 shows the results of the dichroism analysis of anthracene, acridine, and phenazine radical anions for the intense Y-polarized and weak 2-polarized bands. It is apparent that the Y-polarized band is blue shifted in the order of anthracene, acridine, and phenazine, while the shift of 2-polarized band is very slight. These facts can be explained qualitatively by considering the nature of the molecular orbitals concerned with the transitions. The MO scheme of anthracene for these transitions is shown in Figure 7. The Y-polarized (11)and the 2-polarized (111) transitions are represented by the configurations 9,-,* ag and a7 a", respectively. (The contribution of these configurations to each transition is 87 and 75% J These MO's are represented schematically in the figure. The coefficients of atoms 9 and 10 in MO's a7and @a are 0.49, while those in MO agare zero. Hence, when one or both of the carbon atoms of these positions are replaced by nitrogen, MO's and 9,should be stabilized and their energies decreased, while MO agshould be little affected and keep the same energy. Then the difference of molecular orbital energies between a8and a9becomes large in the order of anthracene, acridine, and phenazine, isnd that of a, and aais almost the same in these compounds. Therefore, it can be understood why in these radical anions the Y-polarized bands show large blue shifts while the 2-polarized bands show very small shifts. By making use of the pairing relation between the radical anion and cation,1° when the carbon atoms at positions 9 and 10 are replaced by nitrogen in the case of the radical cation, the energies of MOs 9,and should be decrearsed while that of MO a6is unchanged. It is expected that the Y-polarized band of the radical cations shifb to red in the order of anthracene, acridine, and phenazine. This seems
-
J. Pbys. Cbem.
456
to be in good agreement with observations (see Table 111). Acknowledgment. We are indebted to Dr. T. Shida of Kyoto University for kindly supplying the copies of his experimental data prior to publication. We thank Dr. Y. Inada of Tokyo Institute of Technology and Drs. M. Imamura and M. Hoshino of The Institute of Physical and Chemical Research for their help in measuring the absorption band at near-infrared region.
References and Notes (1) Part 1: Hiratsuka, H.; Sekiguchi, K.; Hatano, Y.; Tanizaki Y. Cbem. Pbys. Lett. 1978, 55, 358. (2) Part 2: Hiratsuka H.; Tanizaki, Y. J. Pftys. Cbem. 1979, 83, 2501. (3) (a) Kira, A,; Koizumi, M. Bull. Cbem. SOC.Jpn. 1969, 42, 625. (b) Masuhara, H.; Okuda, M.; Koizumi, M. Bull. Cbem. SOC.Jpn. 1968, 41, 2319. (c) Zanker, V.; Erhardt, E. 6er. Bunsenges. Pbys. Cbem. 1968, 72, 267.
456-459 (a) David, C.; Janssen, P.; Geuskens, G. Spectrocblm. Acta, Part A 1971, 27, 367. (b) Shda, T.; Kira, A. Bull. Cbem. Soc. Jpn. 1969, 42, 1197. Ezumi, K.; Kubota, T.; Miyazaki, H.; Yamakawa, M. J . Pbys. Cbem. 1978, 80, 980. (a) Chaudhuri, J.; Kume, S.; Jagur-Groctzinski, J.; Szwarc, M. J. Am. Cbem. SOC. 1968, 90, 6421; (b) Schmulbach, C. D.; Hinckley, C. C.; Wasmund, D. J. Am. Cbem. SOC. 1968, 90, 6600. In accordance with the reviewer's comment, we also carried out CNDO/S calculations. The calculated results In the region below 30 X lo3 cm-' are similar to those obtained by the method of a-electron approximation. The n - r * transkions calculated below 30 X lo3 cm-' are very weakly allowed and seem to be neglected in the discussion of the visible absorption spectra in this paper. The a-a' transition energies obtained by CNDO/S calculation are shifted systematically to blue by (1-3)X lo3 cm-' compared with those of the a-electron approximation. The polarized absorption spectra obtained in this experiment are analyzed by use of the method of the a-electron approximation since this method explains well the experimental results. Pariser, R.; Parr, R. G. J. Cbem. Phys. 1953, 21, 767. Shida, T . Kyoto University, private communication. McLachian, A. D. Mol. Pbys. 1959, 2 , 271.
Raman Scattering Study of the Coloration Mechanism of Cathodochromic Sodalite M. K. Badrlnarayan, J. M. Stencel," and L. T. Todd, Jr. Department of Nectrical Engineering, University of Kentucky, Lexington, Kentucky 40506 (Received Ju/y 16, 1979)
The coloration mechanism of cathodochromic bromine sodalite, N~A16Si6024-2Na13r, is studied using Raman scattering techniques. Raman spectra are reported for as-grown sodalite, sensitized (annealed) but uncolored sodalite, electron beam colored sodalite, and bleached sodalite. Several Raman bands are described that change in frequency and intensity as a result of the sensitizing and coloration processes. One band at 460 cm-' is very strong for uncolored sodalite but totally disappears upon coloration of the material. Since this band is assigned to the aluminosilicate cage, the reduction in intensity indicates that one of the electron donor sites in this material is associated with the A1-0-Si cage. This is the first experimental observation of an electron-donor site in sodalite.
Introduction Bromosodalite, Na,&6Si6024.2NaBr, is one of the most widely studied"" cathodochromic materials for use in dark trace cathode ray tubes. Sodalite changes its color, from white to purple, when excited by an electron beam or ultraviolet light. Halogen vacancies must be present in the sodalite structure for coloration to occur. Sodalite materials grown by some methods4 contain the vacancies initially, whereas materials grown by other methodss7 must be annealed in a suitable atmosphere to create the vacancies. Upon exposure, electrons are released from donor sites and captured at halogen vacancies to form F-centers. These centers, with a characteristic absorption band at -5550 A,absorb green light from incident white light and reflect the rest, giving the material its purple coloration. Two modes of coloration exist: a thermal mode and an optical mode. The thermal mode can be erased only by heating the material to -300 "C, whereas optical mode coloration can be erased by exposing the material to light. An understanding of the coloration and erasure mechanisms could lead to the improvement of the device-related properties of the material. The coloration mechanism has been studied by various groups,4-11and various models have been proposed. Electron spin resonance measurements clearly indicate that the F-center electrons are trapped in halogen vacancies a t the centers of sodalite cages, but the location of the electron donors has not yet 0022-3654/80/2084-0456$0 1 .OO/O
been identified. This article reports experimental data related to the donor site, and a possible location of the site is proposed. Raman spectra associated with sodalite have been studied by Angell12 and Stroud,13 but Raman spectra of annealed and colored sodalite have not been previously reported. Variations in Raman mode intensities and frequencies caused by annealing and coloration are reported and discussed. These variations occur as a result of vacancy creation during annealing and charge transfer during coloration.
Experimental Section Sodalite used in this study was grown using a hydrothermal technique, as described by Stroud,l3?l4and sensitized under vacuum a t 825 O C for 60 min7 Raman spectra of uncolored sodalite were obtained from samples packed in a 1 mm diameter brass cylinder that was attached to a goniometer during spectral acquisition. Raman spectra of colored and bleached sodalite were obtained from samples packed in an 8 mm diameter, 1.5 mm deep hole in an aluminum plate. This plate was placed in a demountable cathode ray tube, and the sample was colored to a saturation contrast ratio of 40:l by using a 20-kV anode voltage. The coloration was bleached by heating the sample for 5 min with an Ar+ laser at 5145 A with a power of 1.5 W. 0 1980 American
Chemical Society
