Raman spectroscopic characteristics of phthalocyanine and naphthalocyanine in sandwich-type (na)phthalocyaninato and porphyrinato rare earth complexes

Polyhedron 20 (2001) 557– 569 www.elsevier.nl/locate/poly

Raman spectroscopic characteristics of phthalocyanine and naphthalocyanine in sandwich-type (na)phthalocyaninato and porphyrinato rare earth complexes Part 2. The effects of different excitation wavelengths Jianzhuang Jiang a,c,*, Ursula Cornelissen b, Dennis P. Arnold c,*, Xuan Sun a, Heiner Homborg b,* a

Department of Chemistry, Shandong Uni6ersity, Jinan 250100, People’s Republic of China Institut fu¨r Anorganische Chemie der Christian-Albrechts-Uni6ersita¨t, Olshausenstrasse 40, D-24098 Kiel, Germany c Centre for Instrumental and De6elopmental Chemistry, Queensland Uni6ersity of Technology, GPO Box 2434, Brisbane 4001, Australia b

Received 12 September 2000; accepted 7 December 2000

Abstract The resonance or near-resonance Raman spectroscopic data in the range of 500– 1800 cm − 1 of a series of nineteen naphthalocyaninato (Nc), phthalocyaninato (Pc) and/or porphyrinato (Por) rare earth sandwich complexes including double-deckers M[Pc(OC8H17)8]2 (M=Nd, Ce, Eu, Er), M(Nc*)2 [M= Pr, Nd, Eu; Nc* = Nc(tBu)4, Nc(SC12H25)8], M(Por)(Nc) {M =La, Pr, Eu, Gd; Por= meso-tetrakis(4-t-butylphenyl)porphyrin [T(4-tBu)PP], meso-tetrakis(4-chlorophenyl)porphyrin [T(4-Cl)PP]}, Ce(Por)(Pc) [Por =meso-tetrakis(4-pyridyl)porphyrin (TPyP)], and triple-deckers Eu(Pc)Eu(Pc*)Eu(Pc*) [Pc* = Pc(OC8H17)8], M2(Por)2(Pc) [M = Ce, Sm, Eu; Por=meso-tetraphenylporphyrin (TPP), TPyP, T(4-tBu)PP], and Eu2(Por)(Pc)2 [Por= T(4-Cl)PP, T(4-tBu)PP] have been studied systematically using laser excitation sources emitting at 457.9, 488.0, 514.5 or 647.1 nm. The resonance Raman characteristics for unsubstituted and substituted (na)phthalocyaninato mono-radical anions Pc’−, Nc*’− and dianions Pc2 − are thus described comparatively under a variety of conditions. The intense band at ca. 1491– 1524 cm − 1 attributed to both pyrrole CC and CN aza group stretches was confirmed to be the marker band for Pc’− and Pc2 − anions. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Raman spectroscopic characteristics; Phthalocyanine; Naphthalocyanine; Rare earth sandwich complexes

1. Introduction The sandwich-type phthalocyaninato double-deckers have attracted great attention due to their potential applications in materials science [1,2]. Some proposed fields of use include molecular electronics, molecular optronics, and molecular iono-electronics [3,4]. The search for novel advanced molecular materials has stimulated intense research into substituted bis(phthalocyaninato), bis(naphthalocyaninato), heteroleptic * Corresponding co-authors. Tel.: +86-531-856-4088; fax: +86531-856-5211 (J. Jiang); Tel.: + 61-7-3864-2482; fax: +61-7-38641804 (D.P. Arnold); Tel.: +49-431-880-3262; fax: +49-431-880-1520 (H. Homborg); E-mail addresses: [email protected] (J. Jiang), d.arnold@ qut.edu.au (D.P. Arnold), [email protected] (H. Homborg).

bis(phthalocyaninato), and mixed porphyrinat – (na)phthalocyaninato metal complexes especially since the beginning of the 1990s [5–9]. IR spectroscopy has been proved to be a versatile technique for studying the intrinsic properties of the sandwich bis(phthalocyaninato) complexes M(Pc%)2 (M= rare earth, Th, U, Zr, Hf, Bi, Sn; Pc% =Pc, Pc*) and porphyrinato-phthalocyaninato double-deckers M(Por)(Pc%) (Pc% = Pc, Pc*; M= rare earth, Th, U, Zr, Hf) (for a list of abbreviations, see Appendix A; for general structural formulae, see Fig. 1) [10 –18]. Since the neutral double-deckers of M(III) ions formally contain one macrocycle radicalanion and one dianion, the degree of (de)localisation of the hole is a major point of interest. The study of the triple-deckers allows comparison with the spectra of the macrocyclic dianions. We recently published an exten-

0277-5387/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 2 7 7 - 5 3 8 7 ( 0 0 ) 0 0 6 5 7 - 4

558

J. Jiang et al. / Polyhedron 20 (2001) 557–569

sive IR study of rare earth double- and triple-deckers containing a variety of unsubstituted and substituted (na)phthalocyanines and porphyrins [10]. Raman spectroscopy is potentially another valuable tool in analysing the extent of charge (de)localisation in complexes containing porphyrin or phthalocyanine pradicals. However, in the field of sandwich-type porphyrinato and/or phthalocyaninato metal complexes, Raman spectroscopy has not been as extensively applied as the IR technique [19,20]. Since 1989, both Aroca and Homborg have devoted themselves to the Raman spectroscopic characterisation of rare earth bis(phthalocyaninato) compounds [15,21,22]. In 1994, Tran-Thi et al. compared the FT-Raman spectra (excited at 1064 nm) for a series of sandwich phthalocyaninato and porphyrinato gadolinium and cerium compounds in solution and proposed that the intense line at 1500 cm − 1 is the marker line to estimate the hole (de)localisation involving the Pc moiety [19]. As part of our continuing efforts to develop novel synthetic methodologies and to investigate the ring-ring interaction between or among the macrocycles (porphyrinato and phthalocyaninato ligands), we and our collaborators have applied electrochemical and spectroscopic methods to several series of sandwich porphyrinato and/or (na)phthalocyaninato rare earth compounds [5–9,23]. Recently we systematically investigated the Raman characteristics of phthalocyanine and naphthalocyanine for a large number of (na)phthalocyaninato/porphyrinato and/or (na)phthalocyaninato rare earth complexes using a laser excitation source emitting at 632.8 nm [24]. Because of the presence of intense visible absorption bands due to the Pc and Por ligands, the exact pattern of frequencies and intensities of these Raman spectra are expected to depend on the excitation wavelength(s), especially when in near-resonance with the absorption maxima. Herein we describe and compare the resonance or near-reso-

Fig. 1. General structural formulae of unsubstituted ligands and double- and triple-decker complexes.

nance Raman spectroscopic characteristics for the (na)phthalocyanine ligand in M(Pc*)2, M(Nc*)2, Ce(TPyP)(Pc), M(Por)(Nc), (Pc)Eu(Pc*)Eu(Pc*), and M2(Por)2(Pc), M2(Por)(Pc)2 [Por = TPP, TPyP, T(4Cl)PP, T(4-tBu)PP] using several laser frequencies for excitation.

2. Experimental The sandwich-type rare earth complexes were prepared according to the reported procedures [5,23,25]. Resonance Raman spectra were recorded with a multichannel spectrometer XY (Dilor), equipped with a Spectra Physics model 171 and 2025 Kr+ and Ar+ lasers emitting at 457.9, 488.0, 514.5, or 647.1 nm. The sample was fixed on a rotating steel disk and the spectra were measured at ca. 20 K [26].

3. Results and discussion

3.1. Resonance Raman characteristics of homoleptic double-deckers M(Pc*)2 [Pc* =Pc(OC8H17)8] The previous work on Raman spectra of homoleptic double-deckers by the groups of Aroca [21,27], TranThi [19], Homborg [15,28] and Jiang, Rintoul and Arnold [24] was reviewed in our previous paper [24]. We have now extended our studies of the solid-state Raman spectra of the phthalocyanine ligand in M(Pc*)2 [M= Nd, Eu, Er, Ce; Pc*= Pc(OC8H17)8] by recording the spectra with excitation at= 457.9, 488.0, 514.5 and 647.1 nm, to compare with our previous results obtained with uex = 632.8 nm. The four spectra of Nd[Pc(OC8H17)8]2 are compared in Fig. 2, and Table 1 summarises the frequencies for the four double-deckers and the four wavelengths, together with partial assignments according to our previous scheme [24]. The Raman shifts with laser excitation at 647.1 nm for both tervalent rare earth bis(phthalocyaninato) compounds and the tetravalent cerium bis(phthalocyaninato) complex are almost the same as those recorded with 638.2 nm excitation [24] because of the similarity in excitation wavelengths. Typical enhanced Raman lines around 1508 –1525 cm − 1 for MIII[Pc(OC8H17)8]2 (M=Nd, Eu, Er) and at 1503 cm − 1 for Ce{[Pc(OC8H17)8]2 − }2 were observed. The former has been attributed to a w3 porphyrin-like mode which contains nearly equal CC (pyrrole) and CN (aza group) character for both tervalent rare earth and tetravalent cerium phthalocyaninato double-deckers. By using shorter wavelength excitation lines which are still farther away from resonance with the most intense Q absorption band of M[Pc(OC8H17)8]2 (M=Nd, Eu, Er; umax = 688, 681, 673 nm, respectively), a new Ra-

1511s 1592s

4c

566w 606w 684m 743m

787w 884w 987w 1007w 1113w 1133w 1177m 1277m 1300w 1354w 1377s 1409w

1514s 1598s

4b

563m 625w 684w 743w

786w 883w

1406w 1438w 1504m 1590m

1113m 1131w 1177m 1276s 1301w 1351m

786m 884m 986w

685s 743m

566w

4d

1514s 1592s

1458w

1343w 1383w 1404s

1176m 1208w 1278s 1314w

1410m 1437m 1503s

1010w 1111w 1141w 1177m

566m 629w 684s 743s 753 m 787w 868m

4e

1508s

1342w 1383w 1403m

1314w

1137m 1175m 1207w

786w 868sh

563w 632w 685s 742m

1e

1514s 1596s

1409m

1174m 1209w 1276w

953w 1080w

742w

2b

1515s 1594s

1351w 1386w 1406m

1176m 1210w 1279m

1078w 1113w

689w 743w

564w

2c

b

1, Nd[Pc(OC8H17)8]2; 2, Eu[Pc(OC8H17)8]2; 3, Er[Pc(OC8H17)8]2; 4, Ce[Pc(OC8H17)8]2. uex = 457.9 nm. c uex = 488.0 nm. d uex = 514.5 nm. e uex = 647.1 nm.

a

1362w 1410w 1443w 1505m 1592m

1504m 1591s

1462w

1449w

1114w 1136w 1176m 1277w 1300w

1350w 1382m 1403s

1354w 1388w 1410w

1279w

1140w 1178w

1108m

870w

869w

745w

1077w 1109w 1136w 1175m 1209w

686w 743w 756w

685m 743w 756w

1d

563w

1c

563w

b

566w

1

Table 1 Characteristic Raman bands (cm−1) for RE[Pc(OC8H17)8]2 (RE= Nd, Ce, Eu, Er) a

1516s 1593s

1406m

1344w

1176m 1207w 1280s 1315w

1108m

687w 744w 757w

564w

2d

1513s

1342w

1314w

1084w 1112w 1137w 1175w

787m 870w

563w 631w 686s 743s

2e

1523s 1600s

1414m

1276m

1176w

1113w

687w 742w 758w

3b

1524s 1600s

1462w

1414m

1322w 1353s

1179w 1210w 1280m

1112s

879w

760m

688m

565w

3c

1524s 1600s

1412s

1277s 1318w

1176w

1110s

875w

687m 744m 759m

3d

1523m

1402w 1413s

1138w 1178w

567w 630m 687s 745m 758m

3e

wCa–Cb(pyrr.) wCN wCN wCb–Cb(pyrr.) wCN (aza) wbenzene

benzene breath. lC–H lC-H pyrrole breath. lC–H lC–H lC–H

macrocycle breathing lmacrocycle wC–N (aza)

wCN wCb–Cb (pyrr.) wCN (aza) wbenzene

wCN

wCa–Cb (pyrr.)

lC–H

benzene breath. lC–H lC–H pyrrole breath. lC–H lC–H

macrocycle breathing l macrocycle wC–N(aza)

Assignment

J. Jiang et al. / Polyhedron 20 (2001) 557–569 559

560

J. Jiang et al. / Polyhedron 20 (2001) 557–569

Raman lines of MIII[Pc(OC8H17)8]2 (M=Nd, Eu, Er) at 1508 –1524 cm − 1 and 1592 –1600 cm − 1 seem to experience a blue-shift in the same order. This agrees with the result of Homborg on M(Pc)2 [15,28] and also with that for M[T(4-tBu)PP](Nc) as will be discussed below.

3.2. Resonance Raman characteristics of M(Nc*)2 [Nc* =Nc( tBu)4, Nc(SC12H25)8]

Fig. 2. Resonance Raman spectra of Nd(Pc*)2 [Pc* = Pc(OC8H17)8] with excitation at (A) 457.9 nm, (B) 488.0 nm, (C) 514.5 nm, (D) 647.1 nm.

man line due to the ortho-substituted benzene quadrant stretches around 1590 cm − 1 appears as the most intense band instead of that due to pyrrole CC group and CN aza group stretches at 1508 – 1523 cm − 1. Furthermore, the latter gradually gains relative intensity and becomes more intense than when excited with 647.1 nm radiation. The results for MIII[Pc(OC8H17)8]2 (M =Eu, Nd, Er) collected in Table 1 are consistent with those of Homborg for M(Pc)2 [15,28]. In contrast, for Ce{[Pc(OC8H17)8]2 − }2, the intensity of the line at about 1503 cm − 1 remains unchanged and an additional band with medium intensity appears at about 1591 cm − 1. This difference is attributed to the different electronic absorption characteristics between MIII[Pc(OC8H17)8]2 (M =Nd, Eu, Er) and Ce{[Pc(OC8H17)8]2 − }2 (main Q band: umax =649 nm). It is worth noting that the line in the range of 1276 – 1280 cm − 1 for tervalent rare earth double-deckers appears as an intense one when excited with 514.5 nm; it is of weak or medium intensity in the spectra of MIII[Pc(OC8H17)8]2 (M= Nd, Eu, Er) when excited with 457.9 nm and 488.0 nm radiation and also in the spectra of Ce{[Pc(OC8H17)8]2 − }2 with all four excitation lines (u=457.9, 488.0, 514.5, 647.1 nm). It is also noteworthy that along with the decrease of the rare earth ionic size from Nd to Er, the typical Pc*’−

In contrast to the bis(phthalocyaninato) rare earth compounds, neither the synthesis nor the spectroscopic characterisation of bis(naphthalocyaninato) rare earth compounds has been studied extensively. Before our work on the synthesis, IR and brief Raman spectroscopic characterisation for substituted M[Nc(tBu)4]2 [23 –25], Eu[Nc(SC12H25)8]2 [23,24], and M(TPyP)(Nc%) [Nc% =Nc, Nc(SC12H25)8] [5], only the synthesis, electronic absorption spectra, and electrochemical properties of unsubstituted naphthalocyanine-containing Lu(Nc)2, Lu(Pc)(Nc), and Lu2(Nc)3 have been described [29 –33]. By analogy with the Raman characteristics of sandwich naphthalocyaninato rare earth compounds with excitation at 632.8 nm, the Raman characteristics of M(Nc*)2 [M= Pr, Nd, Eu; Nc* =Nc(tBu)4, Nc(SC12H25)8] were partially assigned and the data are summarised in Table 2. Due to the similar electronic structure and electronic absorption properties among these naphthalocyaninato double-decker complexes, all three compounds show similar Raman characteristics when employing the same excitation line. Because of the similar excitation energy, the Raman spectra of these compounds (u= 647.1 nm) are very similar to those obtained with 632.8 nm [24]. Since this excitation is far away from resonance with the most intense Q absorption band of M(Nc*)2 (M=Pr, Nd, Eu; umax = 783, 786, 784 nm, respectively), the ortho-substituted benzene quadrant stretch (naphthalene) around 1590 cm − 1 appears as the most intense line while the pyrrole CC group and CN aza group stretches at 1510 cm − 1 and 1520 cm − 1 appear as medium lines. When excited with 457.9, 488.0 or 514.5 nm radiation, which are still farther away from resonance with the Q absorption band of naphthalocyaninato rare earth double-deckers, featureless Raman spectra with few and weak Raman peaks were obtained for M(Nc*)2 [Nc*= Nc(tBu)4, Nc(SC12H25)8].

3.3. Resonance Raman characteristics of M(Por)(Nc) As noted by Tran-Thi, the porphyrin ligand and the Pc ligand can be easily distinguished by both the frequencies of their respective characteristic Raman lines and their different intensity patterns [19]. The Qy absorption bands of phthalocyanines are generally much stronger (at least tenfold) and appear at longer wave-

J. Jiang et al. / Polyhedron 20 (2001) 557–569

lengths than those of porphyrins. They are thus in closer resonance with the excitations used here (457.9 –632.8 nm) and so the phthalocyanine contributions appear to dominate the Raman spectra in the mixed Por– M–Pc% sandwich compounds. The characteristic resonance Raman lines for M(Por)(Nc) are given in Table 3. The partial assignments listed for Eu[T(4-Cl)PP](Nc) in Table 3 are based on the similarity of the spectra to those of Eu(Por)(Nc) and Eu(Nc*)2 studied previously using 632.8 nm excitation [24]. The comparison with the spectra of M(Nc*)2 is limited due to the strong fluorescence in running the Raman measurements for Eu[T(4-Cl)PP](Nc) when using excitations other than 647.1 nm. The Raman spectra of M[T(4-tBu)PP](Nc) suffered from strong fluorescence even when using 647.1 nm excitation. Fig. 3 exhibits the typical Raman spectra of Pr[T(4-tBu)PP](Nc) (uex = 457.9, 488.0, 514.5, 647.1 nm). It is clear that the Raman spectra of the mixed porphyrinato and naphthalocyaninato rare earth compounds change significantly depending on the excitation wavelength due to the difference in degree of resonance with the electronic absorption bands. In the Raman spectra with excitation at 457.9 nm, the lines at 1493 – 1506 cm − 1, due to

561

pyrrole CC group and CN aza group stretches, and at 1286 –1292 cm − 1, attributed to aromatic C–H bending vibrations, appear as the most intense Raman lines. By using 488.0 nm excitation, the line at 1286 –1292 cm − 1 loses some intensity and the most intense one appears at 1468 –1480 cm − 1 (pyrrole CC group and CN aza group stretches). The latter shifts to around 1486 –1499 cm − 1 and changes to be the most intense line when excited with 514.5 nm radiation. Interestingly, the energies of these most intense characteristic Nc’− lines seem to depend on the ionic size of rare earth sandwiched in these mixed double-deckers, regardless of the excitation energy. Along with the decrease of rare earth ionic size from La to Gd, all these corresponding Raman lines are shifted to higher energy. This result corresponds well with that for M(Pc%)2 [Pc% =Pc, Pc(OC8H17)8] as mentioned above.

3.4. Resonance Raman characteristics of homo-dinuclear triple-deckers (Pc)Eu(Pc*)Eu(Pc*) [Pc* =Pc(OC8H17)8] The resonance Raman results for triple-decker (Pc)Eu(Pc*)Eu(Pc*) [Pc*= Pc(OC8H17)8] (uex =457.9,

Table 2 Characteristic Raman bands (cm−1) for RE(Nc*)2 [RE= Pr, Nd, Eu; Nc* = Nc(tBu)4, Nc(SC12H25)8] a 5

b

5c

5d

540m 606w 620w 684s 715w 739s 752m 776m 821w 851w 890w 1090m 1126w 1157w 1193s 1218m

619w 683w

811w

811w 953w

1216w

5e

1194w 1219w

1300w 1320w 1371s 1402m

1368m 1401w

6c

6d

615w

616w

684w

683w

810w

813w

978w 1083m 1114w

1085m

1190m 1217w

1191m 1218w

1323w 1373w

1373w 1402m

6e 540m 607w 664w 684s 715w 739s 752w 776w 820w 851w 890w 1090m 1127w 1156w 1192s 1217m 1261w 1302w 1371s 1402m

7b

7c

691w 740w

a

1434m 1537m 1592m 1660m

1589w

1507m 1592s 1630w

1423m 1502m 1587m 1649m

1506w 1592m 1645m

1508m 1592s 1629w

5, Pr(Nc*)2; 6, Nd(Nc*)2, [Nc*= Nc(tBu)4]; 7, Eu[Nc(SC12H25)8]2. uex = 457.9 nm. c uex = 488.0 nm. d uex = 514.5 nm. e uex = 647.1 nm. b

7e

547w

537w

690w

581w 688w

macrocycle breathing

739w 751w 765w

l macrocycle wC–N (aza)

740w

833w

1085w 1121w 1154w 1194m

1194w

1516m 1588m 1629m

1627w

864w 981w 1088w 1128w 1192m 1213m

lC–H lC–H pyrrole breath. lC–H lC–H lC–H

1413w

1301w 1346w 1368s 1398m 1413m

1504w 1585w 1647w

1514m 1586s 1627m

wCb–Cb (pyrr.) wnaphthalene

1350w 1371w

1427w 1514w

Assignment

831w

953w

1414w 1431w 1536w 1593w 1653w

7d

wCa–Cb(pyrr.) wCN wCN

b

1453w 1471m

1362w 1382w

1286s

1220w

1142w 1187m

1030w 1070w

934w 954w

845w

798w

641w 692w

8

1468s

1429m

1357w

1266m 1289w

1169m 1202w

1124w

1017w 1082w

917w 937w

785w 829w

1447w

1370w

1216w 1254w 1276w 1306w

1138w 1173w

1028w

927w 948w

637w

592w 629w 679w

702w

8d

8c

1439w 1456w

1366w

1306w 1346w

1241w

1003w 1023w 1056w 1080w

621w 642w 673w

8e

1434w 1476w

1367w 1388m

1136w 1148w 1182m 1191m 1237w 1290s

1032w 1079w 1104w

938m 957w

775w 804w 847w

644w 683w 698w 726 w

9b

1410w 1437m 1477s

1174m 1209w 1246w 1270m 1293w

1129w

1015w

921w 940w

762w 787w 831w 845w

631w 683w 705w

594w

9c

1452m

1357w 1374w

1307w

1216w 1255w

1138m 1169m

1025w 1072w

928w 947w

765w 793w

688w 710w

9d strong fluorescence

9e

Table 3 Characteristic Raman bands (cm−1) for RE[T(4-tBu)PP](Nc) [RE =La, Pr, Gd] and Eu[T(4-Cl)PP](Nc) a

1435w 1477w

1368w 1389m

1146w 1176m 1190w 1236w 1265w 1292s

1032w 1079w 1104w

937w 956w

578w 606w 644w 682w 698w 723w 757m 774sh 803m 846w

10 b

1413w 1444m 1480s

1369w

1130w 1159m 1174w 1213w 1248w 1274m 1296w

1017w 1087w

922w 942w

763w 791w 832m

686w 707w

595w 633w

10 c

1380w 1426w 1458w

1308w

1138m 1168m 1221w 1257w

1031w 1071w

948w

768w 795w

637w 691w 711w

10 d

1463w

1350w 1386w

1310w

1026w 1057w

644w

10 e

wCN wCb–Cb(pyrr.)

wCN

wCa–Cb(pyrr.)

lC–H

lC–H lC–H pyrrole breath. lC–H lC–H

lC–H lC–H

macrocycle breathing lmacrocycle wC–N (aza)

Assignment

562 J. Jiang et al. / Polyhedron 20 (2001) 557–569

1274w

1289w

1500w

1564w

1484w

1576w

1169w

1120w

11 d

1486s 1566w 1595w

8d

1561s

1450w 1492w

1308m 1350w 1373w 1386w

559w 622 w 644 w 676 w 958w 1025m 1057w 1082w

11 e

1560s 1591w

8e

1581w 1602w

1501s

9b

1547w 1576s

9c 1491s 1564w 1597w

9d

9e

b

8, La[T(4-tBu)PP](Nc); 9, Pr[T(4-tBu)PP](Nc); 10, Gd[T(4-tBu)PP](Nc); 11, Eu[T(4-Cl)PP](Nc). uex = 457.9 nm. c uex = 488.0 nm. d uex = 514.5 nm. e uex = 647.1 nm.

a

1506w

1162w

1178w

1417w

11 c

11 b

8c

1552w 1573w

b

1493s 1576w 1597w

8

Table 3 (Continued)

1575w 1601w

1506s

10 b

1549w 1580w

10 c 1499s 1565w 1597w

10 d 1492w 1561m

10 e

wCN wCb–Cb (pyrr.) wCN (aza) wbenzene

wCN

l C–H l C–H pyrrole breath. l C–H l C–H l C–H wCa–Cb(pyrr.)

macrocycle breathing lmacrocycle wC–N (aza) l C–H l C–H

wbenzene

wCN (aza)

Assignment

J. Jiang et al. / Polyhedron 20 (2001) 557–569 563

J. Jiang et al. / Polyhedron 20 (2001) 557–569

564

488.0, 514.5, 647.1 nm) are tabulated in Table 4 and assigned as previously for 632.8 nm excitation. As expected, the Raman spectrum (uex = 647.1 nm) is quite similar to that when using excitation u= 632.8 nm except for the intrusion of stronger fluorescence. Use of excitation at shorter wavelengths further enhances the fluorescence. However, for the purpose of reference, the corresponding Raman data are listed in Table 4.

3.5. Resonance Raman characteristics of Ce(TPyP)(Pc), M2(Por)2(Pc), and M2(Por)(Pc)2

Fig. 3. Resonance Raman spectra of Pr[T(4-tBu)PP](Nc) with excitation at (A) 457.9 nm, (B) 488.0 nm, (C) 514.5 nm, (D) 647.1 nm.

Table 4 Characteristic Raman bands (cm−1) for (Pc)Eu(Pc*)Eu(Pc*) [Pc* = Pc(OC8H17)8] a b

12

12 c

685w

12 d

681w

1176w

1502m 1593w a

1500m 1593w

1505m 1592w

12 e

Assignment

565w 575w 629w 683s 745m 768w 783w 816m 1106w

macrocycle breath. lmacrocycle wC–N (aza)

1138 w 1181w 1202w 1339w 1404m 1499m

lC–H lC–H pyrrole breath. lC–H lC–H lC–H wCa–Cb (pyrr.) wCN wCb–Cb (pyrr.) wbenzene

12, (Pc)Eu(Pc*)Eu(Pc*) [Pc* =Pc(OC8H17)8]. uex = 457.9 nm. c uex = 488.0 nm. d uex = 514.5 nm. e uex = 647.1 nm). b

The resonance Raman characteristics together with partial assignment [24] for Ce(TPyP)(Pc), M2(Por)2(Pc), and M2(Por)(Pc)2 (u=457.9, 488.0, 514.5, 647.1 nm) are summarised in Table 5. As expected from the similarity of the excitation wavelengths, the Raman spectrum of Ce(TPyP)(Pc) (uex = 647.1 nm) is quite similar to the one excited with 632.8 nm as both wavelengths are in close resonance with the main Q band of Ce(TPyP)(Pc) (630 nm). The sole difference is that the detection of Raman peaks in the range of 1090 –1458 cm − 1 is obscured to some degree due to increased fluorescence in the present case in contrast to the results obtained by the Raman microscope technique [24]. The Raman marker for the phthalocyanine dianion Pc2 − appears as an intense line at 1495 cm − 1, which downshifts by about 10 cm − 1 compared with that of Pc*2 − in Ce(Pc*)2, but corresponds well with that in the triple-decker M2(Por)2(Pc) and M2(Por)(Pc)2 as discussed previously [24]. With excitations (u= 457.9, 488.0, 514.5 nm) farther away from resonance with the main 630 nm Q absorption band of Ce(TPyP)(Pc), the strong wCb –Cb (pyrr.) line at 1495 cm − 1 (uex = 647.1 nm) shifts to 1516 –1521 cm − 1 together with the appearance of a shoulder band at about 1500 –1505 cm − 1. Moreover, a new line due to the ortho-substituted benzene quadrant stretches around 1590 cm − 1 becomes more significant as compared to the situations with excitation at 647.1 and 632.8 nm [24], the greatest enhancement of this medium intensity Raman line being obtained with excitation at 514.5 nm (Table 5). The resonance Raman spectra of (TPP)Sm(Pc)Sm(TPP) and [T(4-tBu)PP]Eu(Pc)Eu(Pc) with the four excitation lines are shown in Figs. 4 and 5, respectively. It is obvious that all the Raman investigations for the triple-deckers M2(Por)2(Pc) suffer from strong fluorescence when excited with 647.1 nm. This is in marked contrast with the results obtained with the Raman microscope technique with similar excitation wavelength (632.8 nm) [24]. However, good Raman spectra were obtained for these triple-deckers with excitations at 457.9, 488.0 and 514.5 nm. It is worth mentioning that the similarity of the Raman spectra of the two classes (Por)M(Pc)M(Por) and (Por)M(Pc)M(Pc) with

J. Jiang et al. / Polyhedron 20 (2001) 557–569

565

Table 5 Characteristic Raman bands (cm−1) for Ce(TPyP)(Pc), RE2(Por)2(Pc), and RE2(Por)(Pc)2 [RE= Ce, Sm, Eu; Por=TPP, TPyP, T(4-tBu)PP, T(4-Cl)PP] a 13

b

13 c

13 d

13 e

14 b

14 c

14 d

14 e

576w

579w 632w

577w

680w

684m

15 b

15 c

15 d

15 e

Assignment

574w 626w 667w 683w

macrocycle breathing

752 782w

lmacrocycle wC–N (aza)

547w 575w 638w 679w 756w

681w

676w 732w

742 w 803w

801w 828w 846w 884w

827w

678w 739w

679w 732w

689w

746 m 775w

800w

820m

828w

779w 795w 833w

822w

933w 953w

916w 937w

884w

897w

1004w

636w

884w 917s 939m

986w 1004w

999w

1004w

987w 1005w

988w 1006w

l C–H l C–H

1005w

1033m 1070w 1090w 1128w 1148w

1083w 1116w 1139w

1085w

1081w 1119w

1078w 1117w

1174w

1139w 1178w

1230s

1230m

1230m

1278m

1278w

1177w 1194w

1195w

1222w

1239w 1260w

1238w 1268w

1231w

1230w 1266w

1078w 1120w

1082w 1118w 1137w 1176w

1078w 1116w

1228w 1266w

1230s 1274w

1298m 1319m 1348w

1343m 1359w

1339m

1403w 1455s 1510s

1493m 1517w 1540w

1494m 1541m

1564w 16

b

1344s

1344s

1391w 1439w

1494s

1493s

1493s

1543s

1540s

1541s

1438w 1477w 1491w 1513w

16

c

16

d

550w

strong fluorescense

681w 731w

16

e

lC–H lC–H pyrrole breath. lC–H lC–H lC–H

1219w 1230w

1302w

1281w 1297s 1312w

1345s

1355w

1333m 1345m 1360m 1393w 1442m

1440w

1495s

1496m

1544s

1541m

lC–H wCa–Cb(pyrr.)

wCN wCN

1394w 1454s 1505s

1447w 1498w

wCb–Cb(pyrr.) wCN (aza)

1563w 1599w

1599w

1599w

b

c

d

17

17

576w

679w 710w 729w

679w 711w 733w

17

17

e

1599w

1599w

b

c

18

18

576w

657w 677w

678w

733w

732w

18

547w 578w

576m

679w

679s 710w 732sh 743s 782w 806w 816m

802w 815w

816w

816w

884w

889w

889w

988w 1007w

989m 1007w

990w 1008w

888w 936w 990w 1008w 1028w

1081w

1080w 1103w

733w

577w

wbenzene d

579w 628w

736 w 782w

779w

1073w

1178m

1554w

594w

680w

1493w

1344m 1360m 1393w 1442w

1068w 1088w 1123w

678w 708w 731w 743 w

781w

18

e

576w

678s 730w 741 m 779w

macrocycle breathing lmacrocycle wC–N (aza)

797w 803w 814w 869w 890w 989w 1008w

1083w

815w 890w 991w 1007w 1029w 1074w

889w 988w 1006w

813w 885w 990w 1008w

1076w

1009w 1030w

937w 990w 1008w 1027w 1079w

1085w 1106w

1103w

1080w 1106w

815w

989w 1007w

1103w

lC–H lC–H lC–H

J. Jiang et al. / Polyhedron 20 (2001) 557–569

566 Table 5 (Continued) 16 b

16 c

16 d

1118w 1137w 1174w

1116w 1137m 1174w

1122w 1178w

1228w 1262w

1231m

17 c

17 d

17 e

18 b

18 c

18 d

1139w

1117w 1138m

1115w

1181w

1137w 1177w 1196w

1115w 1135w 1175w 1195w

1122w 1137w 1178w

1229m 1266w

1230m 1259w

1230m 1260w

1228m

1227w

1228m 1265w

1227m 1264w

1300w 1330sh

1302w 1331m

1301w 1329m

1276w 1298w 1328w

1307w 1330m

1303w 1327m

1346m 1360sh 1397w 1441w 1496s 1542s

1346m 1361m

1346m 1375w

1344m 1359m

1344s

1447w 1497s 1544s 1566w 1596w

1447w 1499s 1543s 1566s

1395w 1443w 1493s 1538s

1444w 1493s 1538s

1446w 1492s 1539s

1608w

1606w

1608w

1330w

1330sh

1330sh

1344w 1361w 1390w 1440w 1495s 1541s

1345s 1359sh 1391w

1345s 1360sh

16 e

17 b 1119w

1495m 1540m 1564w

1496s 1542s

1606w

1608w

19 c

19 d

19 d

684w

563w 629w 685w 725w 744w

1591w 19 b

682w

678w

748w

743w

1177w

1340w 1359w 1422w 1447m 1492m 1542w 1566w

1233m 1263w

1344m

18 e

1217w 1225w

lC–H pyrrole breath. lC–H lC–H lC–H

1299w 1329m 1337m

lC–H wCa–Cb(pyrr.)

1420w 1446w 1494s 1534w

wCN wCN wCb–Cb (pyrr.) wCN (aza) wbenzene

macrocycle breathing lmacrocycle wC–N (aza)

786w 807w 813w 848w

867w 894w

937w 989w 1006w 1029w

987w 1006w 1028w

1105w

1106w

1143w

1140w

1198w

1194w

1138w 1177w 1194w

1228w 1264w

1225w

1224w

1280w 1301w

1278m 1300w 1316w 1342m

992w 1010m 1033w 1087w 1108w

1304w 1347m

1454w 1505sh 1521s 1550m

1343m 1365w 1385w 1404w 1431w 1505sh 1516s 1546m

1597w

1595w

1393w

1403w 1430w 1505sh 1516s 1545w 1558w 1594m

988w 1006m 1028w 1090w

lC–H lC–H

1141w 1164m

lC–H lC–H pyrrole breath lC–H lC–H lC–H

1292w l C–H wCa–Cb(pyrr.) 1363m 1426w

wCN

1458w 1495s

wCN wCb–Cb (pyrr.)

1536w 1557m

wCN (aza) wbenzene

a 13, Ce2(TPyP)2(Pc); 14, Sm2(TPP)2(Pc); 15, Eu2(TPP)2(Pc); 16, Eu2[T(4-tBu)PP]2(Pc); 17, Eu2[T(4-Cl)PP](Pc)2; 18, Eu2[T(4-tBu)PP](Pc)2; 19, Ce(TPyP)(Pc). b uex = 457.9 nm. c uex = 488.0 nm. d uex = 514.5 nm. e uex = 647.1 nm.

J. Jiang et al. / Polyhedron 20 (2001) 557–569

567

the same excitation laser line clearly suggests that the spectra for these different kinds of triple-deckers are dominated by Pc2 − contributions. There is no Raman line that can be readily ascribed to the Por moiety even when the excitation at 457.9 nm (closer to resonance with the Soret band) was used. In both series of tripledeckers (Por)M(Pc)M(Por) and (Por)M(Pc)M(Pc), the w3 porphyrin-like mode (of the Pc moiety) shows two characteristic lines at ca. 1493 – 1505 and 1538 –1544 cm − 1, their relative intensity depending on both the sandwich species and the excitation energy used. These results are in good correspondence with those of Jiang on the Raman spectra of analogous compounds using the Raman microscope technique with excitation at 632.8 [24] and of Tran-Thi on (TPP)M(Pc%)M(TPP) [M = Ce, Gd, Pc% = Pc, Pc(OMe)8] using the FT Raman technique with excitation at 1064 nm [19]. Interestingly, the characteristic patterns of the resonance Raman spectra for these two kinds of triple-deckers are similar to each other and also similar to those reported by TranThi although different excitation laser lines were used.

4. Conclusions With excitation at 647.1 nm, the band at ca. 1503 cm − 1 with contributions from both CC (pyrrole) and

Fig. 4. Resonance Raman spectra of (TPP)Sm(Pc)Sm(TPP) with excitation at (A) 457.9 nm, (B) 488.0 nm, (C) 514.5 nm, (D) 647.1 nm.

Fig. 5. Resonance Raman spectrum of [T(4-tBu)PP]Eu(Pc)Eu(Pc) with excitation at (A) 457.9 nm, (B) 488.0 nm, (C) 514.5 nm, (D) 647.1 nm.

CN (aza group) stretches, is a good Raman marker band for the phthalocyanine dianion Pc%2 − [Pc% =Pc, Pc(OC8H17)8] in double-deckers CeIV(Pc*)2 [Pc*= Pc(OC8H17)8] and triple-decker (Pc)Eu(Pc*)Eu(Pc*) [Pc*= Pc(OC8H17)8]. In Pc*’− radical anion-containing double-deckers MIII(Pc*)2 [Pc*= Pc(OC8H17)8], this band shifts to ca. 1508 –1524 cm − 1 depending on the rare earth ionic radius. When the excitation is farther away from resonance with the Q band absorption of the double-decker Ce(Pc*2 − )2 [Pc*= Pc(OC8H17)8], a medium intensity line around 1590 –1592 cm − 1 assigned to the benzene quadrant stretch of the Pc ring appears as an additional feature of Pc*2 − . A additional line of similar intensity appears at 1592 –1600 cm − 1 for the phthalocyanine monoanion radical Pc*’− in MIII(Pc*)2 [Pc*= Pc(OC8H17)8]. For the same excitation wavelength, the most intense characteristic lines for Pc’− occur at higher energy than those of the corresponding Pc*2 − . The appearance of only the Pc*’− lines in MIII(Pc*)2 (M=Nd, Eu, Er) indicates strong ring –ring interaction and hole delocalisation over both substituted Pc chromophores on the time-scale of Raman spectra. This is in good agreement with the results previously reported by Homborg [15,28] and Jiang, Rintoul and Arnold [24] on a series of sandwich complexes but is in contrast to those for Gd(Pc)2 and Gd(TPP)(Pc) obtained by Tran-Thi [19].

568

J. Jiang et al. / Polyhedron 20 (2001) 557–569

When the excitation is far away from resonance with the Q band absorption of double-decker naphthalocyaninato rare earth complexes, the strongly enhanced Raman line at ca. 1586 – 1592 cm − 1, assigned to the naphthalene quadrant stretch, is a feature typical of naphthalocyanine monoanion radical Nc*’− in M(Nc*)2 [Nc =Nc(tBu)4, Nc(SC12H25)8]. The shorter wavelength excitations are not suitable for recording resonance Raman spectra of M(Nc*)2 due to strong fluorescence. In contrast to the above situation, strong fluorescence interfered for M[T(4-tBu)PP](Nc) even when excited with 647.1 nm, which makes it difficult to compare the Raman spectra among the series of complexes. With excitation at 514.5 nm the most intense characteristic Raman line for naphthalocyanine monoanion radical Nc’− is due to both CC (pyrrole) and CN (aza group) stretches and occurs at ca. 1486 – 1499 cm − 1. This line red-shifted to 1468 – 1480 cm − 1 under excitation at 488.0 nm, but blue-shifted to 1493 – 1506 cm − 1 with excitation at 457.9 nm. In the latter case, a less intense line appears at ca. 1286 – 1292 cm − 1, changing to a very weak one using excitations other than 457.9 nm. The energies of all the most intense naphthalocyanine monoanion radical marker lines blueshift as the size of the sandwiched rare earth ion in the mixed double-decker M[T(4-tBu)PP](Nc) decreases. This is also the case for Pc*’− in PcMIII(Pc*)2 [Pc*= Pc(OC8H17)8]. Further systematic work is in progress to confirm this conclusion. When the porphyrin ligand is changed from [T(4-tBu)PP] to [T(4-Cl)PP] in the mixed double-decker, strong fluorescence interfered when the shorter wavelengths were used, while the Raman spectrum of M[T(4-Cl)PP](Nc) is quite similar to that of its analogue La[T(4-tBu)PP](Nc) when excited at 647.1 nm. The marker line of Pc2 − in the double-decker CeIV(TPyP)(Pc) occurss at ca. 1495 cm − 1 (uex =647.1 nm) but moves to 1501 cm − 1 as a strong shoulder along with another strong line at ca. 1516 – 1521 cm − 1 when excited with 457.9, 488.0 or 514.5 nm radiation. For the Pc2 − dianion in the triple-deckers M2(Por)(Pc)2 and M2(Por)2(Pc) with 647.1 nm excitation, the Raman line appears at 1492 – 1494 cm − 1, and at 1492 –1499 cm − 1 along with a strong line around 1534 – 1543 cm − 1 when the shorter wavelength excitations are used. Thus, the most intense Raman marker(s) for the phthalocyaninato monoanion radical Pc%’− generally occur(s) at higher energy than those of the phthalocyanine dianion Pc%2 − under the same conditions.

Acknowledgements The authors thank the National Natural Science Foundation of China (grant no. 29701002), National Educational Ministry of China, Natural Science Foun-

dation of Shandong Province (Z99B03), State Key Lab of Rare Earth in Peking University, Science Committee of Shandong Province, Shandong University, and the Centre for Instrumental and Developmental Chemistry, Queensland University of Technology (Australia) for financial support. We also thank Dr Llew Rintoul for help in the preparation of the figures.

Appendix A. List of abbreviations M

rare earth metal ion, unless otherwise stated general phthalocyanine H2(Pc%) H2(Pc) unsubstituted phthalocyanine H2(Pc*) substituted phthalocyanine H2(Nc%) general naphthalocyanine H2(Nc) unsubstituted naphthalocyanine H2(Nc*) substituted naphthalocyanine H2[Pc(OC8H17)8] 2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyanine H2[Nc(tBu)4] 3 (4), 12 (13), 21 (22), 30 (31)tetra(tert-butyl)-2,3-naphthalocyanine H2[Nc(SC12H25)8] 3,4,12,13,21,22,30,31-octa(dodecylthio)-2,3-naphthalocyanine H2(Por) general porphyrin H2(TPP) 5,10,15,20-tetraphenylporphyrin H2(TPyP) 5,10,15,20-tetra(4-pyridyl)porphyrin H2[T(4-Cl)PP] 5,10,15,20-tetra(4-chloro)phenylporphyrin H2[T(4-tBu)PP] 5,10,15,20-tetra(4-tert-butyl)phenylporphyrin

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