- Email: [email protected]
Magnetic circular dichroism spectra of benzo[a]pyrene
SpcctrochimicaActa,Vol. 36A.pp.229to231 @ Pergamon RessLtd., 1980. printed inGreatBritain
Magnetic circular dichroism spectra of benzo[a]pyrene H. YAMAGUCHI* Department
of Chemistry,
and M. TATEISHI
Faculty of Science, Kumamoto
University,
Kurokami,
Kumamoto
860, Japan
and T. MURAOKA Department
of Chemistry,
Faculty of Education, (Receiued
Miyazaki
University,
Funatsuka,
Miyazaki 880, Japan
22 May 1979)
circular dichroism (MCD) and absorption spectra of benzo[n]pyrene have been measured. The absorption spectra have been assigned by comparing the experimental results with the signs of FARADAY B terms and transition energies computed by using the PARISER-PARR-POPLE SCFAbatraef-Magnetic
n-MO
CI method. INTRODUCTION
Since benzo[a]pyrene (I) is the strong carcinogen, the electronic structures and spectra of I have been of interest. GERMER and BECKER [l] and PANCIR and ZAHRADNIK [2] have studied theoretically the electronic spectra of I. The magnetic circular dichroism (MCD) spectra of azuleno[5,6,7-cd]phenalene that is found to be carcinogenic [3] and is an isomer of I have been measured by THULSTRUP et al. [4]. They have assigned the absorption spectra of I on the basis of the MCD spectra. TAJIRI et al. [5] have measured the MCD spectra of azuleno[l,2,3-cdlphenalene that is also an isomer of I and they have interpreted its complicated absorption bands. Recently, the MCD has been shown to be a useful tool for the assignment of absorption spectra and for the investigation of the magnetic properties of the ground and excited states of molecules [6-lo]. The purpose of this paper is to assign the absorption spectra of benzo[a]pyrene (I) by measuring the MCD spectra and by comparing the experimental results with the theoretical results obtained by use of the PARISER-PARR-POPLE SCF-r-MO CI method [ll, 121 in combination with the variable bond-length technique [ 131.
where v elhpticity f71. The assuming by BADOZ
MO CALCULATION
The electronic transition energies pole strengths (D) and the FARADAY werecalculatedbythe
* To whom inquiries
the di-
I3 values
of I
PARISER-PARR-PoPLESCF-
RESULTS AND DISCUSSION
Benzo[a]pyrene (I) was commercial product. This compound was carefully purified by recrystallization from ethyl alcohol and was spectroscopically pure, from comparison with published spectra [1,2]. The MCD spectra were measured using a JASCO J-40 A recording spectropolarimeter equipped with a 15.2 kG electromagnet. Absorption spectra were obtained with a Hitachi EPS-3T recording spectrophotometer. All measurements were made on deaerated samples at room temperature. The molecular symmetry of I was so low that only the FARADAY B parameter was extracted from the MCD spectra by use of the formula: [ ([e]&) Jbba”d
(AE),
r-MO CI method [ll, 121 incorporated with the variable bond-length technique [13]. The 56 singly excited configurations were included in configuration interactions. The magnetic and electric moments employed in the evaluation of the FARADAY B values were calculated according to the procedure described by KAITO et al. [15] and evaluated by use of a dipole velocity operator [16], respectively. Liiwdin-orthogonalized atomic basis functions were used for the computation of both quantities [17]. According to CALDWELL and EYRING [18], the FARADAY B terms calculated for a noncentric molecule using an incomplete set of state functions were origin dependent. In this work, origin was set at the midpoint between the centers of charges for the ground and lower five singlet excited states.
EXPERIMENTAL
B = -(33.53)-’
was frequency in cm-l and [e], was molar per unit-field -in units of deg. 1 m-i mol-’ G-i MCD and absorotion spectra were analvzed Gauss type functions with’ the method deschbed et al.[14].
MCD and absorption spectra of I are shown in Fig. 1. As the MCD spectra observed in higher wavenumber region than 42.0 X lo3 cm-’ are rich of noises, we do not show the MCD spectra of this wavenumber region in Fig. 1. The calculated transition energies (AE), dipole strengths (D) and FARADAY B values for I are listed in Table 1 along with the experimental results. The calculated transition energies are in fairly good agreement with the experimental values. The agreement between the calculated and experimental values for D and B is not so good as expected. However, the predicted signs of the B terms agree well with signs of the B terms extracted from the MCD spectra. The
dv,
should be directed. 229
H. YAMAGUCHI,M. TATEISHIand T. MURAOKA
230
1, 0. 0. r L
-0 -0 -1
1 0
12
_$
.? ‘0 ;i8 W L
Y 2 1 0
i
30
25
KCM-'
Fig. 1. Magneuc circular dichroism (top) and absorption (bottom) spectra of benzo[a]pyrene in ethyl alcohol at room temperature.
The first absorption band exists in the wavenumber region of about 22.4~ lo3 to 25.0 x lo3 cm-‘. The MCD spectra of this band exhibit a negative curve. The calculated transition energy for this band is 27.8 x lo3 cm-’ and the calculated FARADAY B term for the transition indicates the positive value (the sign of the FARADAY B term is opposite to the sign of the MCD spectra). The second absorption band is present in the wavenumber of 25.0-32.6 x lo3 cm-‘. The absorption and MCD spectra in this wavenumber region have an abundance of vibrational structures. The O-O peak of the band lies at 26.0~ lo3 cm-‘. The MCD spectra show the positive peaks at 26.0, 27.4 and 29.4 x lo3 cm-’ and the negative peaks at 26.4, 26.8, 28.4, 30.2, 31.4 and 32.6x lo3 cm-‘, respectively. It should be noted that the negative peaks of the MCD spectrum in the second band is very similar to those of the MCD spectrum in the first band in its vibrational mode. It can be expected that the symmetries for the vibrational modes of the positive peaks in the MCD spectrum differ from the symmetries for the vibrational modes of the negative peaks [18].
Table 1. Transition energies(AE), dipole strengths (D) and Faraday B values Theoretical
Experimental
Dt
B*
B/DP
AE*
D+
B*
B/D”
27.8 27.9 35.3
78.0 13.5 0.06
+324.6 -320.6 +0.3
+4.16 -23.80 +5.00
10.5 98.9 5.23 0.06
0.31 6.95 12.1
+0.9 +9.5 -1.7 -4.6
+0.09 +0.10 -0.33 -76.67
+1.20 -0.43 +1.35
+3.87 -0.06
36.6 37.6 37.7 39.0
24.8 26.0 34.1 35.3 36.1 37.8 39.2
1.45 7.36 21.3 17.0
+1.80 +1.30 -1.19 -0.56
AE*
+0.11 +1.24 +0.18 -0.06 -0.03
* In lo3 CR-‘. + In Debye’. * In 10m3Bohr magneton Debye’ cn-‘. * In 10m3Bohr magneton cm-‘.
The third absorption band locates in the wavenumber region of 32.6-37.2x lo3 cm-‘. As shown by Table 1, it seems that this band is composed of three electronic transitions. The fourth absorption band is present in the wavenumber region of 37.2-43.0 x lo3 cm-‘. Table 1 shows that this band is made up from two electronic transitions.
[4] [5]
[6] [7] [8]
REFERENCES
[l] H. A. GERMER,JR. and R. S. BECKER,Theor. Chim. Acra 243, 1 (1972). [2] J. PANCIRand R. ZAHRADNIK, J. Phys. Chem. 77, 121 (1973).
N. B. GIAO and CH. Jwrz, Naturwissenschaften57, 499 (1970). E. W. THULSTRUP, J. MICHLand C. Jvrz, J. Chem. Sot. Faraday Trans. II 9, 1618 (1975). A. TAJIRI, M. HATANO, I. MURATA and K. N~UJI, Chem. Lett. 543 (1976). A. D. BUCKINGHAM and P. J. STEPHENS, Ann. Reo. Phys. Chem. 17, 399 (1966). P. N. SCHATZand A. J. MCCAFFERY,Quart. Reus. Chem. Sot. 23, 552 (1969). D. CALDWELL,J. M. THORNEand H. EYRING,Ann. Rev. Phys. Chem. 22, 259 (1971). J. MICHL,J. Am. Chem. Sot. 100, 6801 (1978). W. GERHARTZand J. MICHL, J. Am. Chem. Sot. 100, 6877 (1978). M. HIGASHI and H. YAMAGUCHI,J. Chem. Phys. 70. 2198 (1979).
[3] N. P. Bw-HOI,
[9]
[lo]
Magnetic circular dichroism spectra of benzdajpyrene [l l] R. PARISERand R. G. PARR, J. Chem. Phys. 21,446 767 (1953). [12] J. A. POPLE, Trans. Faraday Sot. 49, 1375 (1953). [13] H. YAMAGUCHI,T. NAKAJIMA and T. L. KUNII, Theor. Chim. Acta 12, 349 (1968). [14] J. BALXX, M. BILLARDON, A. C. B~CCARA and B. BRIAT, Symp. Faraday Sot. 3, 27 (1969).
231
[15] A. K.UTO, A. TAJIRI and M. I-LUANO,J. Am. Chem. sot. 97, 5059 (1975). [16] A. IMRA, T. H~ANO, C. NAGATA and T. TSURLJTA,Bull. Chem. Sot. Japan 45, 396 (1972). [17] P. 0. L~WDIN, J. Chem. Phys. 18,365 (1950). [18] D. J. CALDWELLand H. EYRING,J. Chem. Phys. 58, 1149 (1973).
Magnetic circular dichroism spectra of benzo[a]pyrene H. YAMAGUCHI* Department
of Chemistry,
and M. TATEISHI
Faculty of Science, Kumamoto
University,
Kurokami,
Kumamoto
860, Japan
and T. MURAOKA Department
of Chemistry,
Faculty of Education, (Receiued
Miyazaki
University,
Funatsuka,
Miyazaki 880, Japan
22 May 1979)
circular dichroism (MCD) and absorption spectra of benzo[n]pyrene have been measured. The absorption spectra have been assigned by comparing the experimental results with the signs of FARADAY B terms and transition energies computed by using the PARISER-PARR-POPLE SCFAbatraef-Magnetic
n-MO
CI method. INTRODUCTION
Since benzo[a]pyrene (I) is the strong carcinogen, the electronic structures and spectra of I have been of interest. GERMER and BECKER [l] and PANCIR and ZAHRADNIK [2] have studied theoretically the electronic spectra of I. The magnetic circular dichroism (MCD) spectra of azuleno[5,6,7-cd]phenalene that is found to be carcinogenic [3] and is an isomer of I have been measured by THULSTRUP et al. [4]. They have assigned the absorption spectra of I on the basis of the MCD spectra. TAJIRI et al. [5] have measured the MCD spectra of azuleno[l,2,3-cdlphenalene that is also an isomer of I and they have interpreted its complicated absorption bands. Recently, the MCD has been shown to be a useful tool for the assignment of absorption spectra and for the investigation of the magnetic properties of the ground and excited states of molecules [6-lo]. The purpose of this paper is to assign the absorption spectra of benzo[a]pyrene (I) by measuring the MCD spectra and by comparing the experimental results with the theoretical results obtained by use of the PARISER-PARR-POPLE SCF-r-MO CI method [ll, 121 in combination with the variable bond-length technique [ 131.
where v elhpticity f71. The assuming by BADOZ
MO CALCULATION
The electronic transition energies pole strengths (D) and the FARADAY werecalculatedbythe
* To whom inquiries
the di-
I3 values
of I
PARISER-PARR-PoPLESCF-
RESULTS AND DISCUSSION
Benzo[a]pyrene (I) was commercial product. This compound was carefully purified by recrystallization from ethyl alcohol and was spectroscopically pure, from comparison with published spectra [1,2]. The MCD spectra were measured using a JASCO J-40 A recording spectropolarimeter equipped with a 15.2 kG electromagnet. Absorption spectra were obtained with a Hitachi EPS-3T recording spectrophotometer. All measurements were made on deaerated samples at room temperature. The molecular symmetry of I was so low that only the FARADAY B parameter was extracted from the MCD spectra by use of the formula: [ ([e]&) Jbba”d
(AE),
r-MO CI method [ll, 121 incorporated with the variable bond-length technique [13]. The 56 singly excited configurations were included in configuration interactions. The magnetic and electric moments employed in the evaluation of the FARADAY B values were calculated according to the procedure described by KAITO et al. [15] and evaluated by use of a dipole velocity operator [16], respectively. Liiwdin-orthogonalized atomic basis functions were used for the computation of both quantities [17]. According to CALDWELL and EYRING [18], the FARADAY B terms calculated for a noncentric molecule using an incomplete set of state functions were origin dependent. In this work, origin was set at the midpoint between the centers of charges for the ground and lower five singlet excited states.
EXPERIMENTAL
B = -(33.53)-’
was frequency in cm-l and [e], was molar per unit-field -in units of deg. 1 m-i mol-’ G-i MCD and absorotion spectra were analvzed Gauss type functions with’ the method deschbed et al.[14].
MCD and absorption spectra of I are shown in Fig. 1. As the MCD spectra observed in higher wavenumber region than 42.0 X lo3 cm-’ are rich of noises, we do not show the MCD spectra of this wavenumber region in Fig. 1. The calculated transition energies (AE), dipole strengths (D) and FARADAY B values for I are listed in Table 1 along with the experimental results. The calculated transition energies are in fairly good agreement with the experimental values. The agreement between the calculated and experimental values for D and B is not so good as expected. However, the predicted signs of the B terms agree well with signs of the B terms extracted from the MCD spectra. The
dv,
should be directed. 229
H. YAMAGUCHI,M. TATEISHIand T. MURAOKA
230
1, 0. 0. r L
-0 -0 -1
1 0
12
_$
.? ‘0 ;i8 W L
Y 2 1 0
i
30
25
KCM-'
Fig. 1. Magneuc circular dichroism (top) and absorption (bottom) spectra of benzo[a]pyrene in ethyl alcohol at room temperature.
The first absorption band exists in the wavenumber region of about 22.4~ lo3 to 25.0 x lo3 cm-‘. The MCD spectra of this band exhibit a negative curve. The calculated transition energy for this band is 27.8 x lo3 cm-’ and the calculated FARADAY B term for the transition indicates the positive value (the sign of the FARADAY B term is opposite to the sign of the MCD spectra). The second absorption band is present in the wavenumber of 25.0-32.6 x lo3 cm-‘. The absorption and MCD spectra in this wavenumber region have an abundance of vibrational structures. The O-O peak of the band lies at 26.0~ lo3 cm-‘. The MCD spectra show the positive peaks at 26.0, 27.4 and 29.4 x lo3 cm-’ and the negative peaks at 26.4, 26.8, 28.4, 30.2, 31.4 and 32.6x lo3 cm-‘, respectively. It should be noted that the negative peaks of the MCD spectrum in the second band is very similar to those of the MCD spectrum in the first band in its vibrational mode. It can be expected that the symmetries for the vibrational modes of the positive peaks in the MCD spectrum differ from the symmetries for the vibrational modes of the negative peaks [18].
Table 1. Transition energies(AE), dipole strengths (D) and Faraday B values Theoretical
Experimental
Dt
B*
B/DP
AE*
D+
B*
B/D”
27.8 27.9 35.3
78.0 13.5 0.06
+324.6 -320.6 +0.3
+4.16 -23.80 +5.00
10.5 98.9 5.23 0.06
0.31 6.95 12.1
+0.9 +9.5 -1.7 -4.6
+0.09 +0.10 -0.33 -76.67
+1.20 -0.43 +1.35
+3.87 -0.06
36.6 37.6 37.7 39.0
24.8 26.0 34.1 35.3 36.1 37.8 39.2
1.45 7.36 21.3 17.0
+1.80 +1.30 -1.19 -0.56
AE*
+0.11 +1.24 +0.18 -0.06 -0.03
* In lo3 CR-‘. + In Debye’. * In 10m3Bohr magneton Debye’ cn-‘. * In 10m3Bohr magneton cm-‘.
The third absorption band locates in the wavenumber region of 32.6-37.2x lo3 cm-‘. As shown by Table 1, it seems that this band is composed of three electronic transitions. The fourth absorption band is present in the wavenumber region of 37.2-43.0 x lo3 cm-‘. Table 1 shows that this band is made up from two electronic transitions.
[4] [5]
[6] [7] [8]
REFERENCES
[l] H. A. GERMER,JR. and R. S. BECKER,Theor. Chim. Acra 243, 1 (1972). [2] J. PANCIRand R. ZAHRADNIK, J. Phys. Chem. 77, 121 (1973).
N. B. GIAO and CH. Jwrz, Naturwissenschaften57, 499 (1970). E. W. THULSTRUP, J. MICHLand C. Jvrz, J. Chem. Sot. Faraday Trans. II 9, 1618 (1975). A. TAJIRI, M. HATANO, I. MURATA and K. N~UJI, Chem. Lett. 543 (1976). A. D. BUCKINGHAM and P. J. STEPHENS, Ann. Reo. Phys. Chem. 17, 399 (1966). P. N. SCHATZand A. J. MCCAFFERY,Quart. Reus. Chem. Sot. 23, 552 (1969). D. CALDWELL,J. M. THORNEand H. EYRING,Ann. Rev. Phys. Chem. 22, 259 (1971). J. MICHL,J. Am. Chem. Sot. 100, 6801 (1978). W. GERHARTZand J. MICHL, J. Am. Chem. Sot. 100, 6877 (1978). M. HIGASHI and H. YAMAGUCHI,J. Chem. Phys. 70. 2198 (1979).
[3] N. P. Bw-HOI,
[9]
[lo]
Magnetic circular dichroism spectra of benzdajpyrene [l l] R. PARISERand R. G. PARR, J. Chem. Phys. 21,446 767 (1953). [12] J. A. POPLE, Trans. Faraday Sot. 49, 1375 (1953). [13] H. YAMAGUCHI,T. NAKAJIMA and T. L. KUNII, Theor. Chim. Acta 12, 349 (1968). [14] J. BALXX, M. BILLARDON, A. C. B~CCARA and B. BRIAT, Symp. Faraday Sot. 3, 27 (1969).
231
[15] A. K.UTO, A. TAJIRI and M. I-LUANO,J. Am. Chem. sot. 97, 5059 (1975). [16] A. IMRA, T. H~ANO, C. NAGATA and T. TSURLJTA,Bull. Chem. Sot. Japan 45, 396 (1972). [17] P. 0. L~WDIN, J. Chem. Phys. 18,365 (1950). [18] D. J. CALDWELLand H. EYRING,J. Chem. Phys. 58, 1149 (1973).