2244
J. Phys. Chem. 1989, 93, 2244-2252
Resonance Raman Spectra and Normal-Coordinate Analysis of Reduced Porphyrins. 2. Copper( I I ) Tetraphenylchlorin and Copper( I I ) Tetraphenylbacteriochlorin Robert J. Donohoe,+Michael Atamian,*and David F. Bocian* Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 (Received: April 4, 1988; i n Final Form: July 25, 1988)
Resonance Raman (RR) data are reported for the Cu(I1) complexes of TPC, TPC-@-d8,TPC-(lSN),, TPBC, TPBC-@-d8, and TPBC-(15N), (TPC = tetraphenylchlorin; TPBC = tetraphenylbacteriochlorin). The RR spectra show that reduction of the porphyrin to the chlorin results in an extremely complicated vibrational pattern due to a low effective symmetry. The further reduction of the chlorin to the bacteriochlorin restores some degree of symmetry and results in a simplified vibrational pattern. Normal-coordinate calculations are performed on the two types of reduced porphyrins, and all-valence force fields are developed for these species. The calculations reveal that the forms of the normal modes of the reduced porphyrins are significantly different from those of the parent tetraphenylporphyrin complex.
Introduction Chlorins and bacteriochlorins are dihydro- and tetrahydroporphyrins, respectively, that serve as the prosthetic groups in photosynthetic and green heme proteins.l-I2 The reduction of the basic tetrapyrrole structure alters the photophysical, redox, and ligand-binding properties of these pigments relative to those of the parent porphyrin.l3-I6 Presumably, the altered physical properties result in more efficacious biological activity for the reduced-pyrrole pigments. Resonance Raman (RR) spectroscopy is a particularly useful tool for exploration of the effects of pyrrole reduction on the properties of the macrocycle. During the past few years, a number of R R studies of chlorins and bacteriochlorins have been rep ~ r t e d . I ~Our - ~ ~group has presented R R studies and normalcoordinate analyses of a series of chlorin, chlorophyll, and bacteriochlorophyll model compounds.24 In these studies, the normal-coordinate calculations were performed by using the semiempirical quantum chemistry force field (QCFF/PI) method of Warshel and K a r p l ~ s . ~The ~ , semiempirical ~~ methodology was used because there are not enough isotopically substituted species available to allow the development of force fields via conventional vibrational analysis methods. Although the normal-coordinate calculations we have reported for the reduced-pyrrole pigments provide insight into their vibrational structure, the semiempirical vibrational analysis procedure is intrinsically less satisfying than a conventional normal-mode analysis. To address this issue, we have now performed normal-coordinate calculations on two reduced-pyrrole species, the Cu(I1) complexes of T P C and TPBC (TPC = tetraphenylchlorin; TPBC = tetraphenylbacteriochlorin), by using an allvalence force field. These calculations were greatly facilitated by the availability of several isotopically substituted pigments and by the development of a valence force field for CuTPP (TPP = tetraphenylp~rphyrin).~~The valence force field calculations reported herein for CuTPC and CuTPBC confirm many of the general features predicted by the QCFF/PI method for the normal-mode structure of reduced-pyrrole pigments.24 Methods Experimental Procedures. Free-base TPC and TPBC were prepared from T P P (Midcentury) according to the methods of Whitlock et a1.28 The TPC and TPBC in chloroform were separated via chromatography on packed talc columns under suction. Free-base TPC-(15N)4and TPBC-(I5N), were obtained from TPP-(15N)4,which was prepared by the method of Lindsey et aLZ9 Free-base TPC-@-d8and TPBC-P-d8 were obtained from TPP'Current address: INC-4, Los Alamos National Laboratory, Los Alamos, N M 87545. 'Department of Chemistry, Michigan State University, East Lansing, MI 48824.
0022-3654/89/2093-2244$01.50/0
P-d,, which was prepared by the method of Shirazi and G ~ f f . ~ ~ Copper(I1) was inserted into TPC by standard procedures3' except (1) Svec, W. A. In The Porphyrins; Dolphin, D., Ed.; Academic Press: New York, 1978; Vol. V, pp 341-399. (2) Sibbet, S. S.; Hurst, J. K. Biochemistry 1984, 23, 3007. (3) Babcock, G. T.; Ingle, R. T.; Oertling, W. A,; Davis, J. C.; Averill, B. A,; Hulse, C. L.; Stufkens, D. J.; Bolscher, B. G.J. M.; Wever, R. Biochim. Biophys. Acta 1985, 828, 58. (4) Morel], D. B.; Chang, Y.; Clezy, P. S. Biochim. Biophys. Acta 1967, 136, 121. (5) Andersson, L. A,; Loehr, T. M.; Lim, A. R.; Mauk, A. G. J . Biol. Chem. 1984, 259, 15340. (6) (a) Peisach, J.; Blumberg, W. E.; Adler, A. Ann. N.Y.Acad. Sci. 1973, 206, 310. (b) Berzofsky, J. A,; Peisach, J.; Blumberg, W. E. J . Biol. Chem. 1971, 246, 3367. (7) Brittain, T.; Greenwood, C.; Barber, D. Biochim. Biophys. Acta 1982, 705, 26. (8) Lemberg, R.; Barrett, J. In Cytochromes; Academic Press: London, 1973: DD 233-245. (9)%mkovich, R.; Cork, M. S.; Gennis, R. B.; Johnson, P. Y. J . A m . Chem. Soc. 1985, 107, 6060. (IO) Chann, C. K.; Barkigia, K. M.; Hanson, L. K.; Fajer, J. J . Am. Chem. S o t . 1986, 168, 1352. ( 1 1) (a) Chang, C. K. J . Biol. Chem. 1985, 260, 9520. (b) Chang, C. K.; Wu, W. J . Biol. Chem. 1986, 261, 8593. (12) Okamura, M. Y.; Feher, G.; Nelson, N. In Photosynthesis; Govindjee, Ed.; Academic Press: New York, 1982; Vol. I, pp 195-272. (13) (a) Scheer, H.; Inhoffen, H. H. In The Porphyrins; Dolphin, D., Ed.; Academic Press: New York, 1978; Vol. 11, pp 45-90. (b) Weiss, C. In The Porphyrins; Dolphin, D., Ed.; Academic Press: New York, 1978; Vol. 111, pp 21 1-223. (14) Stolzenberg, A. M.; Strauss, S. H.; Holm, R. H. J . Am. Chem. S o t . 1981, 103,4763. (15) Feng, D.; Ting, Y.-S.; Ryan, M. Inorg. Chem. 1985, 24, 612. (16) Strauss, S. H.; Thompson, R. J. J . Inorg. Biochem. 1986, 27, 173. (17) (a) Ozaki, Y.; Kitagawa, T.; Ogoshi, H. Inorg. Chem. 1979,18, 1772. (b) Ozaki, Y.; Iriyama, K.; Ogoshi, H.; Ochiai, T.; Kitagawa, T. J . Phys. Chem. 1986, 90, 6105. (c) Ozaki, Y.; Iriyama, K.; Ogoshi, H.; Ochiai, T.; Kitagawa, T. Ibid. 1986, 90, 6113. (18) Cotton, T. M.; Timkovich, R.; Cork, M. S . FEBS Lett. 1981, 133. 39. (19) Ching, Y.; Ondrias, M. R.; Rousseau, D. L.; Muhoberac, B. B.; Wharton, D. C. FEBS Lett. 1982, 138, 239. (20) (a) Andersson, L. A,; Loehr, T. M.; Chang, C. K.; Mauk, A. G.J . Am. Chem. Sot. 1985, 107, 182. (b) Andersson, L. A,; k h r , T. M.; Sotiriou, C.; Wu, W.; Chang, C. K. J. Am. Chem. Soc. 1986,108,2908. (c) Andersson, L. A,; Sotiriou, C.; Chang, C. K.; Loehr, T. M. J . Am. Chem. SOC.1987,109, 258. (21) (a) Cotton, T. M.; Van Duyne, R. P. J . Am. Chem. S o t . 1981, 103, 6020. (b) Cotton, T. M.; Parks, K. D.; Van Duyne, R. P. J . Am. Chem. Sot. 1980, 102, 6399. (c) Cotton, T. M.; Van Duyne, R. P. Biochem. Biophys. Res. Commun. 1978, 82, 424. (d) Callahan, P. M.: Cotton, T. M. J . Am. Chem. S o t . 1987, 109, 7001. (22) (a) Fujiwara, M.; Tasumi, M. J . Phys. Chem. 1986, 90, 250. (b) Fujiwara, M.; Tasumi, M. Ibid. 1986, 90, 5646. (23) (a) Lutz, M. In Advances in Infrared and Raman Spectroscopy; Clark, R. J . H., Hester, R. E., Eds.; New York, 1984; Vol. 11. pp 21 1-300. (b) Robert, B.; Lutz, M. Biochemistry 1986, 25, 2303. (c) Lutz, M.; Hoff, A. L.; Brehamet, L. Biochim. Biophys. Acta 1982, 679, 331. (d) Lutz, M. J . Raman Spectrosc. 1974, 2, 497. (e) Lutz, M. J . Biochem. Biophys. Res. Commun. 1973, 53, 41 3.
0 1989 American Chemical Society
The Journal of Physical Chemistry, Vol. 93, No. 6, 1989 2245
Reduced Porphyrins. 2 4 1 4 ( E X O 4)
60-
,I I1
I1
50
39a:I 14
CUTPBC CUTPC
---
760
I
0
x +o
30-
LL
Figure 1. Absorption spectra for CuTPBC (solid line) and CuTPC (dashed line) in chloroform. The arrows indicate the RR excitation energies. A minor contribution of CuTPC to the spectrum of CuTPBC has been removed by spectral subtraction (e is in units of L mol-’ cm-l).
CuTPBC
CuTPC
Figure 2. Structure and labeling scheme for CuTPBC and CuTPC.
that the reaction was found to proceed quantitatively without heating. The metal was inserted into TPBC by addition of Cu(I1) acetate in 5 mL of dry methanol to a refluxing solution of the free base in 25 mL of chloroform. The solution was allowed to reflux for 40 min under a rigorously oxygen-free atmosphere. With these conditions, the oxidation of CuTPBC to CuTPC is minimized. The absorption spectra of CuTPC and CuTPBC are shown in Figure 1. The R R spectra were acquired on both solid and solution samples. The solid samples were suspended in compressed pellets with a supporting medium of N a 2 S 0 4(3 mg of sample/100 mg of Na2S04)and spun to prevent photodecomposition. For B-state excitation of CuTPC, and solid samples were prepared and maintained under oxygen-free conditions. All solution samples were 1 mg/mL in rigorously oxygen-free chloroform. The Raman spectrometer and laser systems have been previously described.24 The incident power at the sample was typically 4C-50 mW, and the spectral slit width was -5 cm-’. Normal-Coordinate Calculations. The G matrices for CuTPC and CuTPBC were constructed by using the geometry employed for the CuTPP c a l c ~ l a t i o n with s ~ ~ the reduced pyrrole rings approximated as planar moieties with 1.54-A C,C, and 1.45-A C,C, bonds. The geometry of the methylene hydrogens on the reduced rings was taken to be the same as that given in ref 32. Although chlorin and bacteriochlorin complexes are b ~ c k l e d , ~the ~ ”ap~
-
(24) (a) Boldt, N. J.; Donohoe, R. J.; Birge, R. R.; Bocian, D. F. J. A m . Chem. SOC.1987,109,2284. (b) Boldt, N. J.; Bocian, D. F. J . Phys. Chem. 1988, 92,581. (c) Donohoe, R. J.; Frank, H. A.; Bocian, D. F. Photochem. Photobiol. 1988, 48, 531. (25) Warshel, A.; Karplus, M. J . A m . Chem. SOC.1972, 94, 5612. (26) Warshel, A,; Levitt, M. Quantum Chemistry Program Exchange, No. 247, Indiana University, 1974. (27) Atamian, M.; Donohoe, R. J.; Lindsey, J. S.; Bocian, D. F. J . Phys. Chem., previous paper in this issue. (28) Whitlock, H. W.; Hanauer, R.; Oester, M. Y.; Bower, B. K. J. A m . Chem. SOC.1969, 91, 7485. (29) (a) Lindsey, J. S.; Hsu, H. C.; Schreiman, I. C. Tetrahedron Lett. 1986, 27, 4969. (b) Lindsey, J. S.; Schreiman, I. C.; Kearney, P. C.; Marguerettaz, A. M. J. Org. Chem. 1987, 52, 827. (30) Shirazi, A,; Goff, H. M. J . Am. Chem. SOC.1982, 104, 6318. (3 1) Fuhrhop, J.-H.; Smith, K. M. In Porphyrins and Metalloporphyrins; Smith, K. M., Ed.; Elsevier: Amsterdam, 1975; p 798. (32) Kartha, V. B.; Mantsch, H. H.; Jones, R.N. Can. J . Chem. 1973.51, 1149. (33) Spaulding, L. D.; Andrews, L. C.; Williams, G. J. B. J. Am. Chem. SOC.1977, 99, 6918. (34) Gallucci, J. C.; Swepston, P. N.; Ibers, J. A. Acta Crystallogr. 1982, 38B, 2134. (35) (a) Strauss, S. H.; Silver, M. E.; Ibers, J. A. J . Am. Chem. SOC.1983, 105, 4108. (b) Strauss, S. H.; Silver, M. E.; Long, K. M.; Thompson, R. G.; Hudgens, R. A.; Spartalian, K.; Ibers, J. A. J. A m . Chem. SOC.1985, 107, 4207. (36) Fisher, M. S.; Templeton, D. H.; Zalkin, A.; Calvin, M. J. Am. Chem. SOC.1972, 94, 3613.
proximation of planarity is absolutely necessary to make the calculations tractable. Clearly, the approximation is the most severe assumption that is made in the calculations, and the consequences are not readily ascertainable. In this regard, however, we have previously investigated the effects of nonplanarity on the normal-mode structure of chlorins by using the QCFF/PI proc e d ~ r e . ~These ~ J ~ calculations indicate that while the frequencies of the high-energy skeletal vibrations are slightly altered (up to 10 cm-‘) by out-of-plane distortions (of up to a few tenths of an angstrom), the forms of the normal coordinates are Under the geometrical constraints described above, CuTPC and CuTPBC have C, and Ds symmetry, respectively. To retain these symmetries, the normal-coordinate calculations for CuTPC-P-d8 and CuTPBC-P-d8 were performed by presuming perdeuteriation at the C, positions (CuTPC-P-d,,, and CuTPBC-@-d12).Because the C,H2 deformations on the reduced rings of CuTPC and CuTPBC are not extensively coupled with most of the modes on the conjugated portion of the macrocycle, this approximation is not particularly severe. For example, comparison of the calculated frequencies for CuTPBC-P-d12with those of CuTPBC-8-d4 (only unreduced rings deuteriated) reveals that most of the observed deuteriation shifts are associated with the unreduced rings. Vibrations that contain large contributions from motions of the CoH2C,H2 portion of the reduced ring are for the most part not observed. However, a few of the observed modes (two in CuTPBC and three in CuTPC) are calculated to contain small amounts of C,H2 motion. Clearly, the calculated deuteriation shifts for these modes are larger than those that would be calculated for the actual isotopic species studied. The normal modes of CuTPC and CuTPBC were calculated with an all-valence force field by using the vibrational analysis programs of Schacht~chneider.~~ The first step in the vibrational analysis procedure was to obtain a force field for CuTPBC. The vibrational structure for this complex is less complicated than that for CuTPC. Under Ds symmetry, CuTPBC has 55 Raman-active vibrations upon exclusion of the out-of-plane motions of the phenyl groups and the macrocycle (C,H, stretching modes are retained). Only these modes are included in the calculations except for the addition of reduced-ring C,H2 scissor motions, which are slightly coupled to certain in-plane motions of the macrocycle. The resulting 57 modes transform as follows: rvlb= 2 9 ~ , 28BI,
+
The F matrix for CuTPBC was initially constructed by adapting (37) Chow, H.-C.; Serlin, R.; Strouse, C. E. J. A m . Chem. SOC.1975, 97, 7230. (38) Barkigia, K. M.; Fajer, J.; Smith, K. M.; Williams, G. J. B. J. A m . Chem. SOC.1981, 103, 5890. (39) Schachtschneider, J. H. Vibrational Analysis of Polyatomic Molecules; Shell Development Co.: Emeryville, CA, 1962; Vol. 1-111.
Donohoe et al.
2246 The Journal of Physical Chemistry, Vol. 93, No. 6,1989 TABLE I: Valence Force Constants for CuTPBC stretches, mdyn A-' CuN CUN CUC, 'Bc8
(1.111) 1.37 1 5.460 5.649 8.083
stretches, mdyn A-'
(II,IV) 1.460 5.460 3.441 4.144b
CaCmc C,H
NCuN CuNC, CaNC, NCuCm NCUC,
bends, mdyn A rad-2
c8cucm
(IIJV) 0.120"
0.681 2.325 0.519 1.730 0.597"
(1,111) CuCmCu
1.061 2.714 0.597" 0.555 0.597"
CaCmCPh
8'P'H
W,H W,C, HCPH
(1,111) 1.255 0.550 0.080d 0.977 -0.272d -0.150
(II,IV) 0.767 1.083 0.080d 0.650 -0.040d -0.040
cuc~c,9-cuc~c8
cucm-cuc~
cucm-cmcPh
cuc,-cuc, cuc@-c8c@
cacm-cacmcPh
Cacm-caCmcPh
0.544 0.61 1 0.61 1 0.878 0.605 (IIJV) 0.0 0.110" 0.728"
0.200 1.234" 0.728" -0.636 0.977
0.0 0.650 0.500
CmCPh-CPhCPh
1.503
bend-bend, mdyn A radv2
(1,111) 0.160 0.254 0.160
(1I, 1v 1 0.254 0.254 0.0
C,C,&,-C,&,H NC,C,-C,C,C~ cmcuc~-cuc8c,9
(1,111) 0.888 0.888 0.436" 0.538 0.122" 0.122" 0.186" -0.186".'
(1I, I v 1 0.436 0.436 0.436" 0.538 0.122" 0.122" 0.186" -0.1 8 6 " ~ ~
(1,111) 0.0 0.160 0.254
(IIJV) -0.03 1
0.0 0.0
stretch-bend, mdyn rad-'
stretch-bend, mdyn rad-' C,N-NC,Cp C,N-C,NC, C,N-NC,C, CaCm-CuCmCu CuCrn-CmCaC, CuCm-CmC,N
0.544 0.392 0.392 1.255
(1,111) CuCm-C,&,
bend-bend, mdyn A rad-2 C,NC,-NC,C, C,NC,-NC,C,
(II,IV) 0.927
stretch-stretch, mdyn A-'
stretch-stretch, mdyn A-' C,N-C,N C,N-C,C, C,N-C,C, C,N-C,C, C,N-C,C, C,N-C&, CuCm-CuCm
(II,IV) 7.588 4.645b 5.282
CmCPh
bends, mdyn A rad-* (1,III)
(1,111) 7.317 5.243
cac~-cuc,c,
C,C8-NCUC, C,C,-C,C,H C,C&CpH CaC,-CmCaC, c@c8-cuc,c8
C,C,-CpC,H C,C,-C,CpH
(1,111)
(IW)
0.888 0.888 0.225 0.050 0.436" 0.888 0.225 0.050
0.100 0.225 0.0 0.100 0.436" 0.0 0.100 0.100
"Transferred from CuTPP. bTransferred from ref 32. 'C,C, bonds are designated according to the pyrrole ring that contains the a-carbon. dInteraction between alternate bonds. 'Stretch and bend have atom but no bond in common. the force field for CuTPP.,' The initial force constants for the C,H,C,H, portion of the reduced-pyrrole rings were transferred from the force field determined for c y c l o p e n t a n ~ n e . ~In~ the refinement procedure, 45 force constants were varied to fit 59 observed frequencies with an average error of 5.6 cm-I. This refined set of force constants is given in Table I. The bond and angle designations are delineated in Figure 2. As is the case for CuTPP,,' the number of observed frequencies for CuTPBC is substantially less than the number allowed due to the negligible resonance intensity enhancement of certain vibrations. Consequently, the quality of the fit may not be accurately reflected in the relatively small average error in the calculated versus observed frequencies. The intrinsic lack of RR activity for many of the vibrations of CuTPBC requires that the infrared spectra be analyzed in detail to improve the force field substantively. We are currently in the process of analyzing these data. The second step in the vibrational analysis procedure was to obtain a force field for CuTPC. Under C,, symmetry, CuTPC has 1 13 Raman-active vibrations (out-of-plane phenyl and macrocycle motions excluded and reduced-ring C,H, scissors included) which transform as follows: rvlb= 57Al + 5 6 ~ , The substantial increase in the number of Raman-active vibrations for CuTPC relative to either CuTPP or CuTPBC occurs because in-plane modes that transform as E, (D4J or B2" and B3,, ( D Z h ) in the higher symmetry complexes become Raman-allowed under C2, symmetry. Initially, we attempted to fit the vibrational frequencies of CuTPC by using an F matrix constructed by com-
bining the F matrices for CuTPP and CuTPBC. This procedure did not lead to a satisfactory fit of the vibrational frequencies. Subsequently, we began the refinement procedure by using the F matrix of CuTPBC for CuTPC with the appropriate modifications for the additional unreduced pyrrole ring. In the refinement procedure, 33 force constants were varied to fit 79 frequencies with an average error of 6.2 cm-I. This refine force field is given in Table 11. The bond and angle designations are delineated in Figure 2. It should be noted that the refined force field for CuTPC is not of the same quality as those determined for either CuTPP or CuTPBC because the complicated vibrational pattern of the chlorin leads to less certainty in the assignments. These ambiguities in the vibrational assignments for CuTPC may be resolved by the acquisition of RR data for a number of other isotopically substituted species that are not currently available.
Results and Discussion Vibrational Spectra and Assignments. The high-frequency regions of the B,-, Qx-, and Q,-state-excitation R R spectra of CuTPBC are shown in Figure 3. [The intensities of the bands in the Q,-excitation spectrum are artificially attenuated at larger Raman shifts (by a factor of -2 at 1700 versus 1000 cm-I) due to diminished response of the photomultiplier tube at longer wavelengths.] The high-frequency regions of the R R spectra of CuTPC obtained with excitation into the B, Qx(O,O), Qy(O,l),and Q,(O,O) absorption features are shown in Figure 4. The lowfrequency regions of the B- and Q,-state-excitation RR spectra of CuTPBC and CuTPC are shown in Figures 5 and 6, respectively. RR spectra of both complexes were also obtained with other
Reduced Porphyrins. 2
The Journal of Physical Chemistry, Vol. 93, No. 6, 1989 2247 In
a m
!2
/I m m
N
,
m
E
L ‘ .
b)
200
v)
Raman Shift (cm-1)
900
Figure 5. Low-frequency regions of the RR spectra of CuTPBC: (a) By excitation (Aex = 351.1 nm); (b) Qy excitation (Acx = 752.5 nm). C)
Raman Shift (cm-l) l7Oo Figure 3. High-frequency regions of the RR spectra of CuTPBC: (a) By excitation (Aex = 351.1 nm); (b) Q, excitation (A, = 530.9 nm); (c) Qy excitation (A, = 752.5 nm). The By-excitation RR spectrum is
truncated due to the presence of the 363.8-nm laser line. The Raman band due to Na2S04is marked with the symbol #.
are listed in Tables I11 and IV, respectively. The absence of a listed frequency and/or isotope shift indicates that the band is not observed (due to negligible resonance enhancement) or could not be clearly identified (due to poor signal-to-noise and/or overlapping bands). All calculated vibrations are given for CuTPBC. Only calculated vibrational frequencies above 950 cm-’ are listed for CuTPC due to the high spectral density and uncertainty in the vibrational assignments for modes below this frequency. As is the case for CuTPP?’ the eigenvectors of certain modes of CuTPBC and CuTPC are drastically altered upon deuteriation; consequently, isotopic shifts are not given for these vibrations in Tables I11 and IV. The observed and calculated frequencies for these modes are listed in Table V. Examination of the R R spectra of CuTPBC (Figures 3 and 5 ) reveals a fairly simple pattern at all excitation wavelengths. Virtually all of the R R bands are polarized with depolarization ratios ( p ) of -0.33. The excellent correlation of the number of observed and calculated totally symmetric modes confirms that D2h symmetry is a practical approximation for description of the vibrations of CuTPBC. [Accordingly, these polarized modes are derived from the A,, and B,, vibrations of the parent D4h CuTPP complex.] If this were not the case, other polarized modes that originate from either E,, (D4,,)vibrations or out-of-plane deformations would be expected to complicate the R R spectral pattern. There is no clear evidence for strong enhancement of out-of-plane modes. The only candidate for a significantly enhanced E,-type (BZuor B3” in DZhsymmetry) vibration is the band observed at 1465 cm-’ (Figure 3a). The frequency and isotope shifts of this band are not consistent with any calculated A, or B,, mode. Attempts to force this mode into the regression analysis for either of these symmetry blocks uniformly degraded the quality of the overall fit. The observation that p 0.33 for most of the observed R R bands of CuTPBC indicates that a Franck-Condon scattering mechanism predominates for this complex. This result is anticipated due to the large oscillator strengths and energy separations of the absorption features. Non-totally symmetric modes are observed only with excitation in the B-state region. This vibronic scattering is most likely due to coupling between the closely spaced B, and By excited states. It would be useful to obtain detailed B-state excitation profiles to probe the scattering mechanisms in more detail. Comparison of the R R spectra of CuTPC (Figures 4 and 6 ) with those of CuTPBC (Figures 3 and 5 ) clearly shows that the former complex has a far more complicated vibrational pattern than does the latter. At all excitation wavelengths, the spectra of CuTPC are extremely rich. Polarized, depolarized, and anomalously polarized RR bands are observed. Such observations
-
Figure 4. High-frequency regions of the RR spectra of CuTPC: (a) B excitation (A, = 413.1 nm); (b) Q, excitation (hx= 501.7 nm); (c) Qy(O,l) excitation (X,= 580.0 nm); (d) Qy(O,O)excitation (X, = 616.0 nm). The Raman band due to Na2S04is marked with the symbol #.
excitation energies to facilitate the vibrational assignments. The various exciting lines are indicated by the arrows in Figure 1. The observed and calculated frequencies, isotope shifts, and PEDS (potential energy distribution) for CuTPBC and CuTPC
2248 The Journal of Physical Chemistry, Vol. 93, No. 6, 1989
Donohoe et al.
TABLE 11: Valence Force Constants for CuTPC" stretches. mdvn A-l
(IaJIIa) CuN C" C,C,
(Ib,IIIb) 1.068
5.872 5.151
6.560 6.714 8.102
cScS
(IaJIIa) NCuN CuNC, CUNC, NC,C, NC,C, CeC,C,,,
0.120 0.681
0.120 0.681 1.248* 0.519 1.626 0.697
2.509* 0.519 1.730 0.597
0.519 1.730 0.597
C,N-C,N C,N-C,C, C,N-C,C, C,N-C,C, C,N-C,C, C,N-C,C, CeCm-CaCm
0.883 1.17 1 0.080't' 1.053
0.187 0~080'" 1.053 -0. 272b*F -0.1 50'*' 0.992 (1, 2)
0.160 0.254
0.160 0.254 0.160
CaCmCPh
C8Cb'H
C,C,H C,C,C, HCnH
0.703 ( 1 , 2)* 0.544 0.544 0.392 0.392 0.392 0.392 1.255 1.255
(IaJIIa) cucm-c@c8
CaCm-CuC,
c,cm-cmcph C,C,-C,C, C,C,-C,C, CmCph-CphCph
'
0.160 0.254 0.160
0.160 0.254 0.0
(Ia,IIIa)
c,cm-c,c,c, C,C,-C,C,N c,c,-c,C,cph
c,c,-c,cmcph
0.888 0.888 0.436 0.538 0.122 0.122 0.186 -0.186'
(IbJIb) 0.888 0.888 0.436 0.538 0.122 0.122 0.186
-0,186'
(11) 0.888 0.888 0.436 0.538 0.122 0.122 0.186 -0.186'
(IV) 0.436 0.436 0.436 0.538 0.122 0.122 0.186 -0.186
(W
1.146 (3, 0.544 0.392 0.392 1.255
stretch-stretch, mdyn A-' (Ib,IIIb) (11)
0.200b 0.250 1.234b 1,234' 0.72gb O.72gb -0.636' 1.053 1.053 0.728 (1, 2)'
4)* 0.544 0.61 1 0.61 1 0.878 0.605
(IV)
0.200' 0.0 1.234' 0.1 lob 0.728' 0.728' -0.636' 0.0 1.053 0.650' 0.728 (3, 4)'
'
bend-bend, mdyn A rad-2 (IaJIIa) (IbJIIb) (11)
(IV) C,C,C&,CBH NC,C,-C,C,C, C,C,C,&,C~CB
stretch-bend, mdvn rad-l C,N-NC,C, C,N-C,NC, C,N-NC,C, C,C,-C,C,C,
bends, mdyn A rad-2d (IbJIIb) (11)
(Ia,IIIa) CuCmCu
0.883 0.187 o.O8ob'' o.080b~' 1.053 1.053 -0.272b*e -0.040'*' -0.150*" -0.040'9' 1.623 (3, 4)
(IV) 6.601 6.918 5.243' 4.645' 5.508 (3, 4)
7.956 6.278 5.243' 5.243' 5.700 (1, 2)
CmCPh
(IV) 0.767 1.083b
bend-bend, mdyn A rad-2 (IaJIIa) (IbJIIb) (11) C,NC,-NC,C, C,NC,-NC,C, c,c,ce-c,cece
Cucm' C,H
(IV) 0.120 1.061 2.352* 0.597 0.555 0.597
stretch-stretch, mdyn A-' (IbJIIb) (11)
stretches. mdvn A-' (Ib,IIIb) (11)
(IaJIa)
1.460' 6.058 3.441' 4.144'
bends, mdyn A rad-2d (Ib,IIIb) (11)
0.120 0.681
(IaJIa)
(W
(11) 1.371' 6.091 6.249 8.507
0.0 0.160 0.254
0.0 0.160 0.254
0.160 0.254
stretch-bend. mdvn rad-l (IaJIIa) (IbJIIb) (11)
c,c,-c,c,c, C,C,-NC,C, C,Cp-C,CBH C,C,-C,CBH cac8-cmcuc~
c,c,-c,c,c, C,CP-C,C,H C,C,-C,C,H
(IV) -0.031
0.0 0.254
(IV)
0.888 0.888 0.225
0.436*
O.O*
o.o*
0.888 0.888 0.225
0.436 0.888 0.225
0.436 0.888 0.225
0.0
0.0
0.436 0.888 0.225 0.0
0.436 0.0 0.100 0.0
0.888 0.888 0.225
o.o*
o.o* 0.0
o.o*
"The characters in parentheses refer to the macrocycle positions of CuTPC shown in Figure 2. *Transferreddirectly from CuTPBC (Table I). 'C,C, bonds are designated according to the pyrrole ring that contains the a-carbon. dAll force constants of this type were transferred directly from CuTPBC except for those indicated by an asterisk. eInteraction between alternate bonds. 'Stretch and bend have atom but no bond in common.
0 0
I
b)
*O0
Raman Shift (cm-')
900
Figure 6. Low-frequency regions of the RR spectra of CuTPC: (a) B excitation (Aex = 413.1 nm); (b) Qv excitation (Aex = 616.0 nm).
are in accord with previous RR studies of metallo-OEC complexes (OEC = octaethylchlorin).2h~bThe number of polarized R R bands observed for CuTPC is significantly greater than the number observed for CuTPBC. The additional polarized modes primarily
arise from the E,-type vibrations of the parent Ddhcomplex.20b Enhancement of these modes complicates the low-frequency region of the RR spectrum and precludes an assessment of the extent of intensity enhancement of out-of-plane vibrations. The observed depolarization ratios and intensity enhancement patterns for CuTPC indicate that the scattering mechanisms are extremely complicated for this complex. With Q,,(O,O) excitation, all of the R R bands are polarized. As the excitation energy is tuned toward Qy(O,l), depolarized and anomalously polarized bands become enhanced. With Q,-state excitation, these nontotally symmetric modes dominate the spectrum, while both symmetric and non-totally symmetric RR vibrations are observed with B-state excitation. The general appearance of the RR spectra indicate that Franck-Condon scattering occurs with both Qy- and B-state excitation; however, vibronic mechanisms also contribute to the scattering tensor at these excitation wavelengths. Upon Q,-state excitation, vibronic scattering predominates. Whether the Q, state is vibronically coupled to the Qy or to the B states (or all three) is not readily apparent. Detailed excitation profiles are clearly needed to provide any further insight into the scattering mechanisms for this complex. Normal-Mode Descriptions f o r Cu TPBC. The computed vibrational eigenvectors for selected A, and B,, modes of CuTPBC are shown in the left two and right two columns, respectively, of Figure 7 . In the figure, displacements are shown only for those atoms whose motions contribute significantly to the normal mode (10% or greater of the maximum atomic displacement in a given
The Journal of Physical Chemistry, Vol. 93, No. 6, 1989 2249
Reduced Porphyrins. 2
TABLE 111: Observed and Calculated Vibrational Frequencies for CuTPBC
freauencv. - . cm-l Ad8 obsd calcd" I
obsd A8
1
2 3 4 5
6 7 8 9 10 11 12
13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
1601 1598 1543 1456 1353 1301 1273 1243 1074 1037 1009 934 872 835 732d 641 385 213 202
BI8
30 31 32 33 34 35 36 37 38 39 40 41 42 43
1515
55
56 57
3114 3057 3056 3055 2888 1606 1600 1546 1504 1463 1458 1357 1303 1269 1232 1178 1072 1029 1010 1002 930 890 836 733 637 386 255 217 196 3106 3058 3056 3055 2883 1604 1524 1502 1497 1411
1235
44
45 46 47 48 49 50 51 52 53 54
calcd
419
1314 1297 1245 1178 1149 1133 1039 1025 1002 942 812 704 624 498 425 36 1 263 125
obsd
AISN4 calcd
783
0 0 0
0 0 0
763 0
0
2 8
3 7
0 1 1
39
44
C
C
3 4 19
2 13 22
7 8 18
5
5 0
11
310
2 1
0
325d 2 4
0
2 6
C
C
+8
+5 11
+5
1
10
2 0
5 0
Id
2
6 13 2
0 2
4 0
1 0
3
801 0 0 0
773 0
6
6
1
1 15 C
C
26
25 8 24
0 0 0 4
6
C
0
8 4 17 7
4 3 8
C
10
0 0 0 4 1 0 1 0
2
0
2 3 0 1 0 0 0 0 0 0 0 2 0 3 0 0 1 5
1
0 14
C
C
7
C
C
4
C
C
6 2 2
1 C
8
C
40 10 39 27 9 30 8
3 1
1 1
0
4 3 0 0 0
PED (CUTPBC)~ 98% vCOH (1,111) 100% YCphH 100% VCphH 100% UCphH 99% YCOH(I1,IV) 36% VCphCph, 11% &,c, (II,Iv) 31% vC,C, (IIJV), 12% GC,NC, (11,IV) 35% uC,C, (I,III), 8% YC~C,(1,111) 47% 6CphCphCphr 30% YCphCph 45% vC,C, (IJII), 11% yCH, (IIJV) (scissors) 34% -/CH2 (11,IV) (scissors), 17% vC,C, (1,111) 21% uC,N (IIJV), 20% yCH2 (I1,IV) (scissors) 15% YCmcph, 10% YC,N (1,111) 16% uC,N (IJII), 15% uC,N (IIJV) 23% YCmCph, 13% UC,N (I,III), 11% UC,N (II,IV) 84% 6CphH 85% 6CBH (1,111) 48% UCphCph, 28% 6CphH 46% &,c, (I,III), 10% 6CphCphCph 25% YCphCph, 22% vC,c, (1,111) 34% uc,c, (IIJV), 11% YC,C, (I1,IV) 18% UcflC, (II,Iv), 13% VCphCph 14% YC,C, (II,IV), 11% uC,C, (IJII) 30% vC,C, (II,IV), 8% GC,NC, (I1,IV) 4 1% 6CphCphCph 30% 6C,C,C,, 27% vCuN (I,II,III,IV) 67% 6c,c,cph 40% YCUN (I,II,III,IV), 17% 6c,c,cph 21% YC,Cph, 13% 6CphH 99% uCPH (1,111) 100% YCphH 100% VCphH 100% VCphH 99% UCOH(I1,IV) 44% VCphCph, 16% 6CphH 29% uC,C, (IIJV), 19% vC,C, (1,111) 45% 6CphH. 28% VCphCph 25% uC,C, (IJII), 9% bNC,C, (1,111) 71% yCH2 (IIJV) (scissors) 24% uC,C, (I,III), 21% 6C,H (1,111) 41% 6CH2 (II,IV) (Wag), 18% Yc,cph 14% CmCph,13% 6CpH (I,III), 12% uC,N (II,IV) 85% CphH 31% vC,N (IIJV), 12% uC,N (1,111) 23% vC,C, (I,III), 23% 6CpH (1,111) 24% VC,N (I,III)+16% VCphCph 40% 6CphCphCphr 17% VCphCph 70% VCphCph 25% vC,C, (IIJV), 9% GNC,C, (I1,IV) 21% 6C,C,&, (I,III), 18% vC,C, (IIJV) 18% 6c,c&, (I,III), 17% 6CphCphCph 35% GC,C,C, (I1,IV) 37% GNC,C, (I,II,III,IV), 19% 6c,c,cph 17% 6CphCph,Cphr 14% vc,cph, 14% bCuNC, (1,111) 22% bC,C,C, (II,IV), 22% GNC,C, (I1,IV) 62% 6cac,cph, 11% GNC,C, (II,IV) 45% GCUNC, (I,II,III,IV), 30% 6c,c,cph
Deuteriation shifts calculated for CuTPBC-@-d12 (see Methods). Mode descriptors are as follows: Y = stretch, 6 = in-plane deformation; y = out-of-plane deformation. C,, C,, C,, and the characters in parentheses refer to positions of the macrocycle indicated in Figure 2. c p h = phenyl carbon. CNormal-coordinatechanges substantially in isotopic species. See Table V. dTentativeassignment: vibrational feature was not used in the force field fitting procedure. mode). The four Raman-active vibrations that contain the largest amount of C,C, character are shown in the top row of Figure 7. Three of the four modes (no. 7, 8, and 38) exhibit a substantial degree of localization of motion into the symmetry-equivalent C,C, bonds, while the fourth vibration (no. 36) is distributed through all eight C,C, bonds. Four Raman-active modes that display significant C,N displacements are shown in the second row of Figure 7 . This type of motion is distributed into several modes in the mid-frequency
range, and the eigenvectors shown in the figure are those that exhibit the largest degree of localized displacement. The localized A, vibrations, no. 12 and 13, exhibit selective enhancement upon Q,- and Q,-state excitation, respectively (cf. Figure 3b,c). The predicted forms of the normal modes are gratifying in this respect because the atomic displacements of these two vibrations are exclusively directed along the x and y axes of the molecule. The same phenomenon is observed for the C,C, mode (no. 19) shown in the bottom row of Figure 7. Furthermore, certain C,N vi-
The Journal of Physical Chemistry, Vol. 93, No. 6, 1989
2250
Donohoe et al.
TABLE I V Observed and Calculated Vibrational Frequencies for CuTPC
obsd AI
1
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41-57
1601 1598 1591 1563 1529 1517 1464 1441 1373 13561 1299 1286 1260 1248 1236c
1080 1072 1037 1017 1005
calcd 3115 3114 3106 3057 3057 3056 3056 3055 3055 2887 1601 1600 1592 1560 1535 1506 1498 1496 1462 1448 1440 1378 1359 1302 1281 1255 1252 1231 1178 1178 1172 1081 1073 1060 1032 1029 1021 1009 1001 999
