J. Phys. Chem. 1993, 97, 1004-1010
1004
Electronic States of Bis( phtha1ocyaninato)lutetium Radical and Its Related Compounds: The Application of Localized Orbital Basis Set to Open-Shell Phthalocyanine Dimers Naoto Ishikawa, Ommu Ohno, and Youkoh Kaizu' Department of Chemistry, Tokyo Institute of Technology, 0-okayama, Meguro-ku Tokyo 152, Japan Received: June 5, 1992
The ground state and the lowest excited states of lutetium phthalocyanine dimer radical, [Lu(Pc)z] (Pc: phthalocyanine), and those of related compounds, [Lu(Nc)z] and [Lu(Nc)(Pc)] (Nc: 2,3-naphthalocyanine), are studied by configuration interaction calculations on localized orbital basis set. The orbitals, which are localized on either of two ligands, are obtained by a unitary transformation of semiempirical SCMOs of the dimer. The lowest three bands (7 X lo3, 10 X lo3,and 15 X lo3 cm-' for [Lu(Pc)z]; 6 X lo3, 8 X 103, and 13 X 103cm-Ifor [Lu(Nc)z]) areassignedtotheexcitedstates ~ B(IC*)), I 2E1 (ID-))and3E1 (IS-)),respectively. The ground state of the C4" heterodimer, [Lu(Nc)(Pc)], has a population of a hole more in the N c ring than in the Pc ring, The population shifts toward Pc in the 2A2 excited state.
Introduction Bis(phthalocyaninato)lutetium(111)exists in several oxidation states and shows an electrochromic pr~perty.l-~ [Lu(Pc)z] (Pc: phthalocyanine), one of the oxidation states, has an unpaired electron, and its ESR spectrum in solution indicates that the hole is present in *orbitalof phthalocyaninering(~).~,~ Theabsorption spectrum of [LU(PC)~] appears to consist of bands of MPc (metallophthalocyanine), that of MPc'+ (T cation radical of metallophthalocyanine), and an additional broad band peculiar to the dimer in the near-infrared The latter band is also observed with bisporphyrin analogue^.^^-'^ By judging from the absorption spectra, it seems as if the hole in the *-orbital is localized on either of two macrocycles. The X-ray diffraction analysisthat indicates distortion from planarity of one ringls also supports the hole localization.8 On the other hand, NMR, ENDOR,14 and resonance RamanI6 spectra of bisporphyrin analogues show a validity of the delocalization of the hole. To clarify where the hole is, we synthesized a heterodimer (naphthalocyaninato)(phthalocyaninato)lutetium, [Lu(Nc)(Pc)] (Nc:2,3-naphthalocyanine), which consists of two different macrocycles.17 The absorption bands in the Q-band region of [Lu(Nc)(Pc)] ariseat 14.2 X 103 and 10.1 X lO3cm-1. They lie at the middle of the corresponding bands of [LU(PC)~] and [Lu(Nc)~],respective1y.l' This indicatesthat the hole is not localized on either of two macrocycles but delocalized over the two macrocycles. Although MO is often used in the discussion of the electronic structure of dimers, it is not necessarily suitable to see the roles of component molecules in the dimer because it spreads over the whole system. In a previous paper,19we have introduced localized orbital (LO) basis set into the configuration interaction calculation of the excited states of the phthalocyanine closed-shell dimers, [Lu(Pc)J and [(SiPc)20]. The LO basis set is obtained by a unitary transformation of the SCMO basis set of the dimer so that theorbital population on each moiety becomes an extremum; the LOs are produced to be localized on either of two macroIt was shown that the excited states of the dimers are described by the superpositions of exciton coupling states and charge resonance states by means of the LO basis set.19 The purpose of this paper is to characterize the ground and excited electronicstates of lutetium phthalocyanine dimer radical, [Lu(Pc)2],and related complexes, [Lu(Nd2]and [Lu(Nc)(Pc)], by the CI calculation on the LO basis set. Our approach is different from that of Bredas et al.,18which is based on the concept To whom correspondence should be addressed.
0022-3654/58/2097- 1004S04.00/0
of MO. By using the LO basis, the electronic states of thedimer radicals can be characterized in terms of local excitations within individual macrocycles and electron-transfer excitationsbetween macrocycles. It should be noted that the use of the LO basis does not mean the hole localization of the system. A hole-delocalized electronic structure is described as a linear combination of holelocalized electronic configurations.
Calculation The molecular geometry of MPc'+ has been assumed to be the same as that of neutral MPC.~OThe geometries of the MNc and MNc'+ have been supposed as that of MPc attached by four benzo rings. The geometries of the dimer radicals have been assumed as two macrocycles placed in parallel rotating 45O with respect tooneanotherandseparated by3.0A, whichis thedistancc between two mean planes made of a pyrrole carbons in [Lu(Pc)2].'5J9 The charge on the central metal ion was assumed to be neutralized by charge donation from the coordinated nitrogens. Atomic integrals and two electron integrals have been estimated by the same method as the previous paper.19 Interplanar two electron integrals also have been evaluated by ae2/(a + R ) in which a is parametrized.19 The SCMOs and the LOs of closed-shell molecules have been used for the basis of CI calculations of the electronic states of one-electron oxidized corresponding molecule. Electronic States of Monomer Radicals. The ground configuration of the monomer cation radical is made from a closedshell SCF ground configuration by removing one electron from the HOMO n as
IG)= l...aa...nl where n is the 2alUorbital for phthalocyanine and the 3al, orbital for naphthalocyanine. Singly excited configurations are given by ID r a ) = I...aR..,nl
ID r - n ) = I...aa...d
IS r - a )
= {I...ra ...nl- l...~a...nl)/d/z
IT r - a ) = (21...ra ...RJ - l...ra...tzl- l...Pa...tzl]/d6 where r denotes an unoccupied MO. The CI matrix elements between these configurationsare presented in the supplementary material (see paragraph at end of paper). 0 1993 American Chemical Society
Bis(phtha1ocyaninato)lutetium Radical The calculation for MPc'+ (MNc*+)was carried out considering CI among 173 (142) configurations: the ground configuration IC;) and the excited configurations made by the singly (T,T*) excitation from 12 (10) HOMOs into 7 (7) LUMOs (the values in the parentheses are for MNc*+). Eketroaie Statcs of Dimer Radicals. The SCMOs of a dimer are localized onto component macrocycles by a procedure previously presented.19 The molecular integrals including oneand two-electron interactions are also transferred to those of LO basis. Two ground configurationsof the radical dimers are made from the closed-shellSCF ground configuration by removing one electron from highest occupied LOs as follows:
The Journal of Physical Chemistry, Vol. 97, No. 5, 1993 IOOS
I
10
s
I I
I
O J
II I I,
,
40
2 1 1
where the two component rings of the dimer are named A and B,respectively. Occupied LOs are denoted by a, n is the highest occupied LO which belong to A, and m is the highest occupied LO which belong to B. The configuration IGA)means that the hole is localized on B,and IGB)indicates that the hole is localized on A. The interaction between the two configurations is
II
( ~ ~ 1 = 4-(nmm) ~ ~ )
I
Here& the Fockoperator defined with closed-shellconfiguration given by
IR) = l...ua...nRmfil
.
30
20
0 l
10
20
L
30
II
I 40
L
Wavenumber / 10 em.'
Off-diagonal Fock matrix elements between two occupied LOs of different components do not necessarily vanish.19 If A is equivalent to B,the interaction gives electronicstates represented as follows:
Figure 1. Calculated excitation energies and oscillator strengths of (a) MPc, (b) MPc'+, (c) MNc, and (d) MNc'+ where (a) is from previous work.*O The oscillator strengths Ad) are evaluated with the transition dipoles.
IG-) = (lGA)- IGB)}/d2
The electronic states of [Lu(Pc)2], [Lu(Nc)(Pc)], and [Lu(Nc)l] werecalculated with taking intoaccount the twoground configurations and 560 singly excited configurations from the highest 18 (9 per ligand) occupied LOs to the lowest 8 (4 per ligand) unoccupied LOs.
+
IG+) = (IGA) IGB))/d2
IC;-) is the ground state on the condition that (nmm) is negative. If A and B are different from each other, the mixing is displaced from the fifty-fifty linear combination. Single excitation configurations from the reference configuration IC;") are given as follows:
IDAr c m ) = l...ua...nM
where r represents an unoccupied LO. The singly excited configurations from JGB)denoted by IDB p a ) , IDB ~ n ) JSB , rcm),pBrcu),ITBrcm) andpBrca)arealsomadesimilarly. The matrix elementsof the electronicconfigurationsare presented in the supplementary material. The matrix elements between configurations produced from identical reference configuration are formally same as those of MO basis set except that some off-diagonal Fock matrix elements do not vanish.
Results and Discussion (1) Electronic States of the Monomer Cation Radicals. ( a ) Phthalocyanine Cation Radical. Figure 1b shows calculated excitation energies andoscillator strengths of MPc'+. The ground state lA1, of D4h phthalocyanine cation radical has a hole in the 2al, orbital. Electronictransitionsto E, excitedstates are allowed. Table I shows calculated wave functions of the ground state and excited states of MPc*+. The first allowed excited state, lEg, is mainly ascribed to ID 6e,+2alu). The calculation fairly well reproduces not only the excitation energy of the Q band but also the energy shift accompanied by the oxidation: from 14.1 X lo3 to 11.5 X lo3 cm-1 (the present work); from 14.9 X 103 to 12.1 X lo3 cm-' (experimental data for [Mg(Pc)] and [M~(PC)]'+~I).The decrease in intensity of the Q band accompanying the oxidation is also reproduced. Stillman et al. reported detailed deconvolution of absorption spectra and magnetic circular dichroism (MCD) spectra and presented that all major bands except a band at 20 X 103 cm-1 show A-term dispersions which indicatethat the bands are assigned to degenerate transitions, while the 20 X lo3 cm-1 band gives B-term extremum.21 The calculation predicts two candidates for the B-term band. One possibility is to assign the band to an allowed excited state which is calculated between the Q band and B band, namely, either 2E, or 3E, state. They are, respectively, mainly described by an excitation from an occupied e, orbital into the half-occupied 2aIuorbital. In this case, orbital angular momentum of the state
Ishikawa et al.
1006 The Journal of Physical Chemistry, Vol. 97, No. 5, 1993
TABLE I: Calculated Ground State and Excited Doublet States of a Metallophtluloeyanine Catiolr Radical of D" Symmetry wave function
0.00
ground state
1A1 ,= +0.979)G)
+
+ ... + ... ... ... +
11.47 18.35 20.02 20.09 22.14 22.21 22.90 24.72 27.12 27.53
0.0823,0.3120 forbidden 0.0187,0.0282 forbidden forbidden forbidden 0.1159.0.2072 forbidden forbidden forbidden
27.58
0.0618,0.2708
+0.0781T 6eW+3e,) 0.078p 6e,63e,) + 0.07SlS 6eW+4e,) + 0.075p 6e,+4e,) ... 1E, = +0.9611D 6e,+2al,) -t 0.1521S 6eW+4a2,) + 0.1151D 2alu+3c,) + 0 . l l q D 2al,+4ep) + 1A2, = +0.8621D 2alU+4a2,) 0.2671D 2alU+3a2,) 0.243p 6e,+5e,) 0.243p 6%+Se,) 2E, = +0.7921D 2al,+Se,) -t0.334T 6eU+3b2,) - 0.269p 6eW+4a2.) + 0.263p 6eW+3a2.) + ... 1B2, = +0.8271D 2alU+3b2,) -t0.3141T 6e,+5e,) + 0.3141T 6ew+5c,) 0.199p3blu+3azu) + 2A2, = +0.7981D 2alU+3a2,) 4-0.3721D 2alU+4a2,) - 0.214p 6e,+SeW) 0.214p 6e,+5eP) + lBl, = +0.7831D 2al,+2bl,) 0.3731D 3blu-2alU) - 0.278p 6e,+4eW) 0.278p 6e,+4ew) ... 3E, = +0.837(D 2al,+4e,) + 0.295p 6e,+2b1,) + 0.215p 6 e P + l a d 0.173lD 2a1,+5egr) + ... 2AI, = +0.8231D 2al,+lal,) + 0.3041T 6e,+4ew) 0.304p 6e,+4eP) -0.223p 3blu+2bl.) + ... 2BI, = +0.8591D 3bl,+2al,) + 0.38611) 2alu+2bl,) - 0.1561s 6e,+4e,) 0.15615 6++4e,) + ... 2B2, = +0.8271D 4b2,+2al,) 0.2391T 5a2,--2blu) + 0.235lT 4b2,+lalU) 0.207p 7e,+4eW) + 0.2071T 7e,+4e,) + ... 4E, = +0.6221T 6ew+4a2,) 0.501)D 2alu+3e,) - 0.406lS.6e,+4a2,) + 0.1981D 2alU+5e,) +
32.27
0.7441, 1.5947
7E,, = +0.5331S 6eBy+4a2,) + 0.4621s 6e,+-Zbl,)
+
-
+ + + + +
-
+
+
...
+ 0.3221D 2alU+3e,) + 0.2871s 6e,+lal,)
+ ...
The oscillator strengthsf(p) andf(d) are evaluated with the transition velocities and the transition dipoles, respectively.
must be small so that the contribution of A term is scarcely detectable. This assignment reasonably rationalizes the intensity of the band. Another possibility is to assign the band to nondegenerate excited state as Stillman et al. concluded.2' The calculation results in a sequence of symmetry-forbidden excited states in the 18 X 103-25 X lo3cm-I region. Each state is mainly attributable to the excitation from a low-lying nondegenerate occupiedorbital to the half-occupied 2al,orbital. They can obtain the transition intensityonly if the molecular structure is deformed. For example, when the molecular symmetry is lowered to by the doming of the phthalocyanine ring, the 2AI, state (Az state in Cb) is granted a z-polarized transition moment. In such condition, AI, and A*,, states interact under magnetic field, and a B term may appear. However, it is difficult to explain the observed large intensity comparable to the other allowed excited states. To give a correct assignment of the band, further consideration is needed. The 4E, state, which has the IT 6e,+4azy) configuration as a main component, obtains its intensity mostly from IS 6eg+4azu) configuration. From its energy and intensity, the obserwd band at 25 X lo3 cm-1 may be ascribed to the excitation into the 4E, state. In the B-band region, several allowed excited states exist. The most intensively allowed excited state in the region is the 7E, state which is chiefly made of IS 6eg+4a2,). This situation is comparable with that of neutral MPc. The intensity of the B band manifold of MPc is mostly given by the I16eg+4azu)excited configuration.20 (b) 2,3-Naphthalocyanine and Its Cation Radical. 2,3Naphthalocyanine can be regarded as a phthalocyanine molecule whose conjugated system is expanded. Figure 2 shows the MO energy levels of MNc. 3aluand 8eg orbitals correspond to the HOMO and LUMO, respectively. The SazUorbital lies at lower energy than the 3b1, and 7e, orbitals, while the next HOMO of MPc is the 4azUorbital. The HOMO-LUMO energy gap of MNc is smaller than that of MPc; on the other hand, the gap between the HOMO and the highest occupied az, orbital is mostly unaffected by the expansion of the conjugated system. This coincides with VEH calculationson H2Pcand 2,3-H2Nc by Br&s et a1.22 Figure IC and Table IIa present calculated excited states of neutral MNc. Seventy singly excited configurations from the highest 10 occupied MOs to the lowest 7 unoccupied MOs were considered in the CI calculation. The 1E,state is described mostly by a single configuration as l18eg+3aIu). The state is shifted to a lower energy than that of MPc. The red shift is ascribed to the decrease in the HOMO-LUMO energy gap. The 2E, state described by (19eg+3a1u)is located at 21.4 X lo3 cm-1. The
eV -1
-2
-3 6%
-4
--
-- se,
-5
-6
-7
-8
-9
-10
-1 1
Figure 2. Energy diagram of molecular orbitals of MPc and MNc.
shoulder band at the red of the B band may be assigned to the 2E, state. In the Bband region, two major bands, transitions to 3E, and 4&, are predicted. Both states are given transition intensities mostly by J18es+Sazu) configuration. The results of the calculation on the cation radical, MNc'+, are presented in Figure Id and Table IIb. One-electron oxidation causes a bathochromic shift of the lowest energy electronic transition of MNcsimilarly with thecaseof MPc. Thecalculated
Bis(phtha1ocyaninato)lutetium Radical
The Journal of Physical Chemistry, Vol. 97, No. 5, 1993 1007
TABLE Ii: C~lculrtedAllowed Excited Sinslat States of M e t d l o r u p h t h a k y h (I)
8 d
CItiOB R 8 d i d (b) of Ddr SY"etrY
Allowed Excited Doublet State of Its
~~
103 cm-1
a
f(~),~f(d)~
13.14 21.43 30.14 3 1.04
0.2905, 1.2362 0.0452,0.0784 0.3179,0.9640 0.7868, 1.7561
0.00 10.59 18.52 20.68 23.38 26.85 30.06 30.63 3 1.35
ground state 0.1755,0.5029 0.1903,0.4243 0.0796,0.2012 0.0168,0.0319 0.1300,0.2716 0.5002, 1.0934 0.0028,0.0384 0.1063.0.2052
wave function (a) IE,, = +0.96618cW-3a~,) - O.22218eW+5a~,)- 0.071(8e,+4a~,) - 0.06514blU+7e,) 2E, = +0.99319eW+3alu) + 0.076(8cW+5a~,)+ O.046(8e,+4azu) + 0.042(9e,+2alU) 3E, = +0.75718eW+3b~,) + 0.49418eW+5a~,)- 0.22318cW+2a~,) + 0.18718e,+4a2,) 4 K x = +0.69418e,+Sa~,) - 0.35418eW+3bl,) - 0.32418c,+4b~.) - 0.273)5b2,6e,)
]AI,
IE, 2E, 3E, 4E, 5E, 6E, 7E, 8E,
+ ...
+ .,. + ... + ...
(b) +0.980)G) + 0.0851s 8 ~ , + 7 ~ ) + 0.0851s 8~,+7e ) - 0.0681s 4blu-3bl,) + ... = +0.964(D 8eW+3a~,) + 0.1 19p 8cW+Sa2,) + 0.1 15b 3a1~+7c,) - 0.0941D 9e,*3a1,) + = +0.844(D 3alU+7c,) + 0.3331T 8e,+3b1,) 0.1831D 9eY--3alu) - 0.16W 9e,+2a1,) + = +0.5491D 9eW+3al,) + 0.373lT 5b2,+7eW) + 0.352r 6a2,+7%) - 0.336/T 9ey,+3bl,) = +0.8301D 3al,+6eW) + 0.2921T 8eW+4b2,) - 0.236r 8e,+4a~,) - 0.2041D 9e,+3a1) + = +0.812)S 8c,+3blU) - 0.3511T 8c,-3blU) + 0.2131s 8e,+2alU) - 0.145p 8e,+2alu) + = +0.6621s 8eW+5a2,) - 0.5691T 8eW+5a2,) - 0.279)s 8eW+4a2,) - 0.1691D 3al,dc,) = +0.789)S 8e,+2alu) - 0.323p 8eW+2aly) - 0.2591s 8e,+3blu) + 0.2391s 8eW+4a2,) + = +0.694(S 8eW-4b2,) - 0.4351T 8eW+4b2,) + 0.2511s 8eW*4a2,) - 0.lSOg 8c,--2alU) + ...
... ... + ... ... ... + ... ...
-
The oscillator strengths f(p) and Ad) are evaluated with the transition velocities and the transition dipoles, respcctively.
energy (10.59 X IO3 cm-I) is also in good agreement with the experimentalresult( 1O.OX lO3cm-I for [Si(Nc)(OCI3H&]*+ 23). 2Eg mainly consists of ID 3al,-7e,). The observed second absorption band at 13.6 X lo3 cm-I 23 can be assigned to 2E, according to its energy and intensity. Among the bands around the B-band region, the 6E, state chiefly made of IS 8eg+5a2,) has the largest intensity. ( 2 )ElectroaicStatesoftbeDhnerRadicals. ( a )Phthalocyanine Dimer Radical: [tu(Pc)z]. [Lu(Pc)J has two equivalent macrocycles, therefore its wave functions are described by the fifty-fifty admixtures of the corresponding configurations generated from different reference configurations, ICA)and ICB). Considering the reference configurations and six singly excited configurations from the highest occupied LOs into lowest unoccupied LOs, ground and excited states are given by
IG) =
1 31
I 15.
"-3
1
161 1El
2E 1
I
l5E1 4E 1
gE1 11E1
- IGB>]/d2
(G*) = (IGA)+ IGB))/d2
* IDBj + a ) ] / d 2 = (ISAj+a) * ISB k+b)]/d2
ID*) = (IDAk+b)
1%)
ID-) = (IDA6e:+2ayu) and 3E1 has the configuration
IT*) = (ITAj-a) f ITBk4-b)]/d2
IS-) = (ISA6et+2afu) - ISB6e:+2ayu)]/d2
in which a is the highest occupied LO of A, b is that of B, j is the lowest unoccupied LO of A, and k is that of B, respectively. ID-) IC), and IS-) IG) are allowed transitions. Although the interaction between IDAk+b) and IDBj+a) is equal to zero, the states ID+) result from indirect interactions via other configurations. The IT-) state can obtain an intensity only through the configuration interaction with the ID-) state and the Is-) state. The transition to the nondegenerate excited state IG*) is allowed, and its transition moment is z polarized (z axis is perpendicular to the Pc plane). In the previous work, the bands of [Lu(Pc)*] at around 7 X lO3,IO X IO3, and 15 X lo3 cm-I (6 X l O 3 , 8 X 103, and 13 X IO3 cm-1 for [Lu(Nc)2]) are tentatively assigned to the transitions IG*) IG), ID-) JG),and IS-) JG) , respectively.1 Figure 3 shows calculated excitation energies and oscillator strengths of [Lu(Pc)z] on the LO basis set with a = 1.1, which gives the best reproduction of the experimental result. Table I11 presents wave functions of the ground state and allowed excited doublet states of [Lu(Pc)z]. It shows that the ground state 1A2 is ascribed to IG),and the first allowed excited state 1BI is assigned to lG*). The calculated transition energy 6.16 X lo3cm-I is in fair agreement with the experimental data. The transition
-
-
-
-
- IDB6 e t b 2 a f u ) ) / d 2
-
as a main character, respectively. Transition moments of the two configurations are related by (S- lmG) = d 2 ( D - IMG)
However, theintensityof 2EIstate isconsiderablyreduobdbecause of the configuration interaction between ID-) and the other forbidden configurations, namely (IDA6et+2aFu)
- IDB6ei-2afu))/d2
IT-) = (ITA6ef+2afu)
- ITB6e~+2ayu))/d2
The interactionwith IS-)which is located at higher energy reduces the intensity as well. On the other hand, 3El has a much greater intensity than the other states in the region from the near-IR to Q band. The state preserves a character of S I excitation of monomeric phthalocyanine: the singletlike HOMO-LUMO excitation within ring A and that within ring B. The line width of the Q band of the dimer radical is nearly equal to that of monomer. The spectral shape including vibronic structure is also substantially conserved in the dimer. On the
Ishikawa et al.
1008 The Journal of Physical Chemistry, Vol. 97,No. 5, 1993
TABLE III: Ground State and Allowed Excited Doublet States of [Lu(Pc)z] R a d i d of M Basis
Ddd
Symmetry Calculated with u = 1.1 on
Ground State 1A2= -0.6971GA) 0.6971GB)- 0.039(TA6eUB+5ewB)- 0.0391TA6eWB+SeWB)+ 0.0391TB6eWA+5euA)+ 0.0391TB6eWA+5eWA)+ ...
+
Excited States lBI = +0.6951GA) 0.6951GB)+ 0.0491TA6eWB+5euB)+ 0.049(TA6egxB+SegrB)+ 0.049(TB6eWA+5ewA)+ 0.0491TB6eWA+SePA) + ... lEl, = +0.6221TA 6ePAb2alUA)- 0.6221TB6eWB+2aluB) - 0.283)DA6eWB+2aluB)+ 0.2831DB6ePA+2aluA)+ ... 2EI, = -0.5351DA 6eWB+2aluB)+ 0.535(DB6ePA+2aluA)- 0.3971DA6eWA+2aluB)+ 0.3971DB6eWB+2alUA) + ... 3EI, = +O.5961SA 6eWA+2alUA) - 0.596(SB6eWB+2aluB) + 0.215(DA6cWB+2aluB)- 0.2151DB6eWA-2aluA)+ ... 4E1, = +0.529)DA 6eWA-2aluB)-0.5291DB 6eWB+2aIUA) + 0.2831SA6eWA+2aluA)- 0.2831SB6epxB+2aluB)+ ...
+
+
+
+ + +
9EI, = +0.312lTA 6e,A+3b2uA) 0.3121TB6eWB+3bzUB) 0.2781TA6e,A+3a2uA) - 0.278(TB6e,B+3a2uB) ... 10EI, = +0,2441SA6e,A+4azuA) - 0.244(SB6e,B-4a2uB) + 0.2411TA6eWA+4azuB) - 0.2411TB6egyB-4azuA)+ ... 1 lEl, = -0.288)TA 6~,~+4a2,,~) + 0.288(TB6egyA+4azuA) - 0.2721TA6egyA+4azuB) 0.2721TB6 ~ , ~ + 4 a 2 ~ ~... ) 14E1, = -0.3541SA6eWB+3azuA)+ 0.3541SB6eWA+3azuB)+ 0.274)SA6ewA+4a2uA)- 0.2741SB6eWB+4azuB)+ ... 15EI, = +0.3371SA6egrB+3bzUB) 0.337(SB6ewA+3b2uA)+ 0.3211SA6eUB-3bzUA) + 0.321(SB6e,A-3b2uB) ...
+
+
TABLE I V Ground State and Allowed Excited Doublet States of [Lu(Nc)z] Radical of D4d Symmetry Calculated with u = 1.1 on
M Basis
Ground State 1A2 = -0.700(GA)+ 0.700(GB)- 0.0451SA8 e w B ~ 7 e u B-)0.045(SA8ePB+7eWB)+ 0.045(SB8eUA+7euA) + 0.045ISB 8e,A-7eWA)
+ ..,
Excited States 1BI = +0.697)GA) 0.697(GB) 0.052)SA8eUB+7ewB)+ 0.0521SA8ePB+7ePB) + 0.0521SB8eWA+7ewA) 0.0521SB 8eWA+7eWA) lEl, = +0.6141TA 8eWA+3aluA) - 0.6141TB8ePB-3alUB) - 0.2821DA8egXB+3aluB)+ 0.2821DB8eWA+3alUA) + ... ~ E I=, -0.4341DA 8ePA+3aluB) + 0.4341DB8eWB+3aluA) - 0.3901DA8eWB+3aluB)+ 0.3901DB8ePA+3aluA) ... ~ E I=, +0.4991SA 8eWA-3aluA)-0.4991SB 8eWB+3alUB) + 0.4311DA8ePB+3aluB)-0.4311DB 8eWA+3aluA)+ ... ~ E I=, +0.S141DB 8ePB+3aluA) - 0.5141DA8ePA+3alue) - 0.2871SA8eWA+3aluA)+ 0.2871SB8ePB+3aluB) ... ~ E I=, +0.5781DA 3alUB+7eWB) - 0.5781DB3aluA+7eWA)+ 0.2011TA8e,B+3b1uB) - 0.2011TB8ePA+3bluA)+ ... ~ E I=, +0.2971TA 8ePA-3bluA) - 0.2971TB8eUB+3bluB)- 0.283(TA5b~,,~+7e,~)- 0.283(TB5b2UB+7e,B) ... 7E1, = +0.4841TA 8eWA+5azuA) - 0.484(TB8e,B+Sa2uB) + 0.2531TA8e,B+5a2uA) - 0.2531TB8e,A+5a2uB) + ...
+
+
+ ...
+
+ + +
+
+
9E1, = -0.3361SA8e,A+5a2uA) 0.3361SB8egVB+5azuB) - 0.2901SA8ewB+5a2uB)+ 0.2901SB 8e,A+Sa2uA) ... 1 lEl, = -0.3921SA8egxB+3bluA)+ 0.3921SB8e,A+3b~uB) + 0.2531SA8e,A+-Sa2uA) - 0.2531SB8eUB+5azuB)+ 1
...
21
3E 1
4 1
5E
I
g2 10
0
20 Wavenumber/ 103cm"
30
40
0
10
20 Wavenumber/ 10~cm.l
30
40
Figure 4. Excitation energies and oscillator strengths of [Lu(Nc)2] calculated with a = 1.1 on the LO basis (lower) and observed absorption spectrum (upper).
Figure 5. Excitation energies and oscillator strengths of [Lu(Nc)(Pc)] calculated with a = 1.1 on the LO basis (lower) and observed absorption spectrum (upper).
other hand, the Q band of the closed-shell dimer, [Lu(Pc)z]-, is much broader than that of the monomer. It can be due to the difference in portions of interligand excitation configurations, which should largely change the equilibrium core structure. 3E1 excited state of the dimer radical contains almost no interligand excitation, while 2EI state of the closed-shell dimer contains a charge resonance configuration:
BrCdas et al. reported the VEH calculation of [ L U ( P C ) ~ ] . ~ ~ The calculation predicted the four transitions which are almost degenerate two-by-two (centered at 1.71 and 2.02 eV) and have almost the same intensity in the Q-band region. However, it does not reproduce the experimental spectrum. Their calculation would be improved if configuration interaction was considered. ( b ) Naphrhalocyanine Dimer Radical: [Lu(Nc)z]. The calculational results on [Lu(Nc)2] are presented in Figure 4 and Table IV. Assignments of the absorption bands in the near-IR to Q-band region are similar to those of [Lu(Pc)2]. From the calculated energies and intensities, the bands at 6 X lO3,8 X lo3, and 13 X lo3 cm-I are assigned to excited states 1B1,2EI, and 3E1, respectively. Thegroundstate 1Al predominantlycomprh IG), and lBI does IG*). 2E1 has {IDA 8et+3ayu) - IDB 8e:-3a;u))/d2 configuration, more than
16e,
-
2aIuCR+) = (16e:+2atu)
+ 16et+2ayu))/2/2
as a second dominance.19 The present calculation on the dimer radical confirms the previous assignment of the absorption spectrum." The bands of [Lu(Pc)z] at around 7 X 103, 10 X 103, and 15 X l o 3 cm-1 are assigned to the transitions to lBI (main configuration is IC*)), 2El (ID-)),and 3EI (IS-)),respectively. The calculation also suggests that another allowed excited state, lEl, which chiefly contains the IT-) configuration lies at near-IR region. This state is granted an intensity from ID-)configuration.
ID-) = (IDA8e:+3ayu) - IDB8et-3a;u))/d2 however, intensity is borrowed from the latter configuration. 3EI
Bis(phtha1ocyaninato)lutetium Radical
The Journal of Physical Chemistry, Vol. 97, No. 5, 1993 1009
TABLE V Ground State and Allowed Excited Doublet States of [Lu(Nc)(Pc)] Radical of Cr, Symmetry Calculated with a = 1.1 on LO Basis ~
Ground State 1A2= +0.7461GA) - 0.648(GB)+ 0.049pA 8eWB+7eWB)+ 0.049)SA8epB+7egxB) + ... Excited States IE, = +0.7581TA 6epA+2aluA) + 0.3521DB6egXA+2aluA) + 0.3041DA6egXA+3aluB)+ 0.2991TB8epB+3aluB) + ... 2A2 = +0.739)GB) 0.649)GA)+ 0.054)TB6eWA-5eWA) + 0.054)TB6ewA+5ewA) + ... 2E, = +0.7371TB8epB+3aluB) + 0.4431DA8egxB+3aluB)- 0.405(TA6epA+2aluA) + 0.2191DB8epB+2alUA)+ ... 3E, = +0.5921DA6tpA+3aluB) 0.5601DB6esxA-2alUA) + 0.3191DA8egXB+3aluB) + 0.2871SB8epB+3aluB) + ... 4E, = +0.4721DB 6egxA+2aluA) 0.464(SA6ewA+2aluA)- 0.4221TB8egXB+3aluB) + 0.4021DA8epB+3aluB) ... 5E, = +0.5681SB 8egxB+3aluB)- 0.490(SA6egxA-2aluA) - 0.4581DA8epB+3alUB) + 0.250(DB6epA+2aluA) + ... 6E, = +0.6051DA 6eexA+3aluB) 0.4441SB8ewB+3aIuB)+ 0.4291DB8epB+2akuA) - 0.396[DA8e,B+3aluB) + ... 7E, = +0.61 llSA6ewA+2alUA)+ 0.434)DB6epA+2aluA) + 0.3801DA6e A+3a~uB) + 0.3341SB8epB+3aIUB) ... 8E, = +0.805(DB8epB+2alUA)+ 0.387(SB8egxB+3aluB)- 0.322(TB8egxr+3a~uB)+ 0.234(DA8ewB+3alUB)+ ...
+
-
involves
IS-) = {ISA8et-3a;")
- ISB8 e ~ - 3 a ~ u ) ) / d 2
as a main component. (c) Heterodimer Radical: [Lu(Nc)(Pc)]. The two ligands of [Lu(Nc)(Pc)] aredifferent from each other, so that wave functions are displaced from the fifty-fifty admixture of the corresponding configurations. It has been suggested that unsymmetric IS-) state of [Lu(Nc)(Pc)] is located between the symmetric IS-) state of [Lu(Pc)z] and that of [Lu(Nc)2], and a weak transition to IS+) emerges at higher energy regi0n.l' Figure 5 shows calculated excitation energies and oscillator strengths of [Lu(Nc)(Pc)]. Table V shows wave functions of the ground state and excited states. Here, ring A is Pc and ring B is Nc. The molecular symmetry is lowered to C., The ground state is Az, and optically allowed excited states are Az and E. The ground state has a greater coefficient for IGA)than for IGB).This implies that the hole populates more in Nc ring than in Pc ring in theground state. On the contrary, the population shifts toward Pc in 2A2 excited state. The shift results because the energy of the highest occupied LO of Pc, 2aIuA,is lower than that of Nc, 3aluB. In other words, the diagonal energy term of IGA) is lower than that of (GB). The observed band at 14 X lo3 cm-I is assigned to the 5E state from its energy and intensity. The 5E state has (SB 8e:+3aru) and ISA 6etc2a:J as main characters and corresponds to unsymmetric IS-). The calculation reproduced the result that the prominent intensity of the Q bands of the symmetrical dimers is retained in the heterodimer. Conclusion The electronic states of metallophthalocyaninecation radical, MPc'+, have been calculated by considering configuration interactions. The Q band of MPc*+is assigned to lE, which is mainly composed of ID 6eg+2aIu). Two allowed excited states, 2E, (mainlyattributable toID2alu+5e,)) and 3E,(ID 2alu+4e,)) are predicted between Q band and B band. The 7E, state which is chiefly made of IS 6eg+4atu) has its largest intensity in the B-band region. Thecalculation on the electronic states of MNc*+ have been also carried out. The absorption band at 10.0 X lo3 cm-l is assigned to the lowest excited state lE, which mainly consists of ID 8eg+3alu). Among the bands around the B-band region, the 6E,state, whose main character is IS 8eg+5azu), has the largest intensity. The electronic structure of dimer radicals [Lu(Pc)z], [Lu(Nc)~],and [Lu(Nc)(Pc)] have been investigated on LO basis set. By the use of the LOs, the excited states are characterized in terms of intraligand and interligand excitation configurations. In the case of symmetrical dimers, [Lu(Pc)2] and [Lu(Nc)z], the bandsat7X lO3cm-I ([L~(Pc)~])and6X lO3cm-1 ([LU(NC)~]) are assigned to the excitation from the ground state lAz (attributable to IG)) to the excited state lBI (IC*)).The calculated transition energies are in fair agreement with the
+
+
experimental data. The bands at 10 X lo3cm-I ([LU(PC)~]) and 8 X lo3 cm-I ([Lu(Nc)z]) are assigned to the 2EI state mainly composed of ID-),which represents a character of the transition from the half-occupied HOMO to LUMO of cation radical monomer. The bands at 15 X lo3 cm-I ([LU(PC)~]) and 13 X lo3cm-I ([Lu(Nc)z]) are attributed to the 3E1 state chiefly made of IS),which is a superpositionof the singletlikeHOMO-LUMO excitation within ring A and that within ring B. The reason for the similarity in shape of the Q band of the dimer and monomer is that the 3EI state contains almost no interligand excitation, which should largely change the equilibrium core structure. In the case of the C , heterodimer ([Lu(Nc)(Pc)]), wave functions are displaced from a fifty-fifty admixture of corresponding configurations. The ground state, 1A2, has a greater population of the hole in the Nc ring than in the Pc ring. The population shifts toward Pc in the 2A2 excited state. Theobserved band at 14 X lo3cm-I is assigned to the 5E state, which has ISB 8e;-3a:") and ISA 6eA+-2afu) as main characters. The predominant intensity of t i e Q band was reproduced for both of the symmetrical dimers and the heterodimer. Acknowledgment. We thank Prof. Hiroshi Kobayashi, at the Department of Chemistry,Kitasato University,for many valuable discussions. This work has been partially supported by the Nissan Science Foundation. Supplementary Material Available: Matrix elements of electronicconfigurationsontheMO basisset (thecaseofthemonomer that has a hole) and matrix elements of electronic configurations on the LO basis set (the case of the dimer that has a hole) (8 pages). Ordering information is given on any current masthead page. References and Notes (1) Kirin, I. S.;Moskalev, P. N.;Makashev, Y.A. Russ. J. Inorg. Chem. 1967, 12, 369. (2) Moskalev, P. N.; Kirin, I. S.Russ. J . Phys. Chem. 1972, 46, 1019. (3) Corker, G. A.; Grant, B.; Clecak, N. J. J . Electrochem. Soc. 1979, 126, 1339. (4) Riou, M.-T.; Auregan, M.; Clarisse, C. J . Electroanol. Chem. 1985, 187, 349. ( 5 ) L'Her, M.;Cozien, Y.;Courtot-Coupez,J. C. R. Acod. Sci. Paris, Ser. 11 1985, 11, 487. (6) Chang, A. T.; Marchon. J.-C. Inorg. Chim. Acta 1981, 53, L241.
(7) Andre, J.-J.; Holczer, K.; Petit, P.; Riou, M.-T.; Clariue, C.; Even, R.;Fourmigue, M.; Simon, J. Chem. Phys. Lett. 1985, 115,463. (8) Markovitsi, D.; Tran-Thi, T.-H.; Even, R.; Simon, J. Chem. Phys. Lett. 1987, 137, 107. (9) Tran-Thi, T.-H.; Markovitsi, D.; Even, R.; Simon, J. Chem. Phys. Lett. 1987, 139, 207. (10) Castaneda, F.; Piechocki, C.; Plichon, V.;Simon, J.; Vaxiviere, J. Electrochim. Acto 1986, 31, 131. (11) Clarisse, C.; Riou, M. T. Inorg. Chim. Acto 1987, 130, 139. (12) Buchler,J. W.; Els6sser,K.; Kihn-Botulinski,M.;Scharkrt, B.;Tansil. S.ACS Symp. Ser. 1986, 321, 94. (13) Buchler, J. W.; Scarbert, B. J. Am. Chem. Soc. 1988, 110, 4272.
1010 The Journal of Physical Chemistry, Vol. 97, No. 5, I993 (14) Buchler. J. W.: Hiittermann, J.; LBfflcr, J. Bull. Chem. Soc. Jpn.
I*,
bl,71. (15) De Cian, A.; Moussavi, M.; Fischer, J.; Weiss, R. Inorg. Chem. 1985,
3162. .----
21. -
(16) Donohoc, R. J.; Duchowski, J. K.; Bocian, D. F. J . Am. Chem. Soc. 1988. 110,6119. (17) Ishikawa, N.;Ohno,O.; Kaizu,Y. Chem. Phys. Lett. 1991, 180, 51. (18) Ortl, E.; BrCdas, J. L.;Clarisse, C. J. Chem. Phys. 1990, 92, 1228.
Ishikawa et al. (19) Ishikawa, N.; Ohno, 0.;Kaizu, Y.; Kobayashi, H. J . Phys. Chem. 1992, 96, 8832.
(20) Ohno, 0.;Ishikawa, N.; Matsuzawa, H.; Kaizu, Y.; Kobayashi, H. J . Phvs. Chem. 1989, 93, 1713. (2i) Ough, E.; Gasyna, Z.; Stillman, M. J. Inorg. Chem. 1991,30,2301. (22) Ortl, E.; Piqueras, M. C.; Crespo, R.; Br&as, J. L. Chem. Morer. 1990.2, 110. (23) Unpublished data.
