Spectroscopic and luminescence studies on square-planar platinum(ll) complexes with anionic tridentate 3-bis(2-pyridylimino)isoindoline derivatives

Article abstract of DOI:10.1021/ic902019s

Reactions of 1,3-bis(2-pyridylimino)isoindoline (HL1 ), 1,3-bis(2-pyridylimino)benz(f)isoindoline (HL2), or 5,6-dihydro2,3-diphenyl-5- (pyridin-2-ylimino)pyrrolo[3,4-b]pyrazin-7-ylidene)pyridin-2-amine (HL3) with Pt(tht)₂Cl₂ (tht = tetrahydrothiophene) afforded the corresponding Pt(L)Cl complexes. A series of neutral platinum(II) alkynyl complexes Pt(L)(C≡CR) were prepared by reactions of the precursors Pt(L)CI with alkynyl ligands through Cul-catalyzed platinum acetylide σ coordination. Crystal structural determination of Pt(L3)Cl (3), Pt(L1)(C≡CPh) (4), and Pt(L1)(C≡CC₆H₄Bu ^t-4) (6) by X-ray crystallography revealed that the neutral platinum(II) complexes with monoanionic tridentate L ligands display more perfect square-planar geometry than that in platinum(II) complexes with neutral tridentate 2,2':6',2"-terpyridyl ligands. Both the Pt(L)Cl and Pt(L)(C≡CC₆H₄R-4) complexes exhibit lowenergy absorption at 400-550 nm, arising primarily from π → π^*(L) intraligand (IL) and 5d(Pt) →π ^*(L) metal-toligand charge-transfer (MLCT) transitions as suggested from density functional theory calculations. They display bright-orange to red room-temperature luminescence in fluid dichloromethane solutions with microsecond to submicrosecond ranges of emissive lifetimes and 0.03-3.79% quantum yields, originating mainly from ³IL and ³MLCT excited states. Compared with the emissive state in Pt(L)Cl complexes, substitution of the coordinated Cl with C≡CC₆H ₄R-4 in Pt(L)(C≡CC₆H₄R-4) complexes induces an obviously enhanced contribution from the ³[π(C≡ CC₆H₄R-4) → π^*(L))] ligand-to-ligand charge-transfer (LLCT) triplet state. The photophysical properties can be finely tuned by modifying both the L and alkynyl ligands. The calculated absorption and emission spectra in dichloromethane coincide well with those measured in a fluid dichloromethane solution at ambient temperature. 2010 American Chemical Society.

Full text of DOI:10.1021/ic902019s

2210 Inorg. Chem. 2010, 49, 2210–2221
DOI: 10.1021/ic902019s
Spectroscopic and Luminescence Studies on Square-Planar Platinum(II)
Complexes with Anionic Tridentate 3-Bis(2-pyridylimino)isoindoline Derivatives
Hui-Min Wen,† Yu-Hui Wu,† Yang Fan,† Li-Yi Zhang,† Chang-Neng Chen,*,† and Zhong-Ning Chen*,†,‡
†State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter and
Graduate School of CAS, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China, and ‡State Key
Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of
Sciences, Shanghai 200032, China
Received October 13, 2009
Reactions of 1,3-bis(2-pyridylimino)isoindoline (HL1), 1,3-bis(2-pyridylimino)benz(f)isoindoline (HL2), or 5,6-dihydro-
2,3-diphenyl-5-(pyridin-2-ylimino)pyrrolo[3,4-b]pyrazin-7-ylidene)pyridin-2-amine (HL3) with Pt(tht)2Cl2 (tht = tetra-
hydrothiophene) afforded the corresponding Pt(L)Cl complexes. A series of neutral platinum(II) alkynyl complexes
Pt(L)(CtCR) were prepared by reactions of the precursors Pt(L)Cl with alkynyl ligands through CuI-catalyzed
platinum acetylide σ coordination. Crystal structural determination of Pt(L3)Cl (3), Pt(L1)(CtCPh) (4), and
Pt(L1)(CtCC6H4But-4) (6) by X-ray crystallography revealed that the neutral platinum(Π) complexes with
monoanionic tridentate L ligands display more perfect square-planar geometry than that in platinum(II) complexes
with neutral tridentate 2,20:60,200-terpyridyl ligands. Both the Pt(L)Cl and Pt(L)(CtCC6H4R-4) complexes exhibit low-
energy absorption at 400-550 nm, arising primarily from π f π*(L) intraligand (IL) and 5d(Pt) f π*(L) metal-to-
ligand charge-transfer (MLCT) transitions as suggested from density functional theory calculations. They display
bright-orange to red room-temperature luminescence in fluid dichloromethane solutions with microsecond to
3
submicrosecond ranges of emissive lifetimes and 0.03-3.79% quantum yields, originating mainly from IL and
3MLCT excited states. Compared with the emissive state in Pt(L)Cl complexes, substitution of the coordinated Cl with
3
CtCC6H4R-4 in Pt(L)(CtCC6H4R-4) complexes induces an obviously enhanced contribution from the [π-
(CtCC6H4R-4) f π*(L)] ligand-to-ligand charge-transfer (LLCT) triplet state. The photophysical properties can
be finely tuned by modifying both the L and alkynyl ligands. The calculated absorption and emission spectra in
dichloromethane coincide well with those measured in a fluid dichloromethane solution at ambient temperature.
Introduction
last few years in view of their intriguing spectroscopic and
photophysical properties.1-3 They afford extensive applica-
tions in ion sensor,1c luminescence signaling studies of
biological interest,4 photocatalytic hydrogen production,5
and light-emitting materials.6 These planar platinum(II)
complexes can be aggregated along the vertical direction by
intermolecular π-π and Pt-Pt interactions, resulting in
Square-planar platinum(II) complexes with tridentate che-
lating ligands have been attracting great attention over the
*To whom correspondence should be addressed. E-mail: czn@fjirsm.ac.
cn (Z.-N.C.), ccn@fjirsm.ac.cn (C.-N.C.).
(1) (a) Eryazici, I.; Moorefield, C. N.; Newkome, G. R. Chem. Rev. 2008,
108, 1834–1895. (b) Castellano, F. N.; Pomestchenko, I. E.; Shikhova, E.; Hua, F.;
Muro, M. L.; Rajapakse, N. Coord. Chem. Rev. 2006, 250, 1819–1828. (c) Wong,
K. M. C.; Yam, V. W. W. Coord. Chem. Rev. 2007, 251, 2477–2488. (d) Ziessel,
R.; Diring, S. Tetrahedron Lett. 2006, 47, 4687–4692.
(4) (a) Cummings, S. D. Coord. Chem. Rev. 2009, 253, 1495–1516. (b) Ma,
D.-L.; Shum, T. Y.-T.; Zhang, F.; Che, C.-M.; Yang, M. Chem. Commun. 2005,
4675–4677. (c) Clark, M. L.; Green, R. L.; Johnson, O. E.; Fanwick, P. E.;
McMillin, D. R. Inorg. Chem. 2008, 47, 9410–9418. (d) Wu, P.; Wong, E. L. M.;
Ma, D. L.; Tong, G. S. M.; Ng, K. M.; Che, C. M. Chem.;Eur. J. 2009, 15,
3652–3656.
(5) (a) Du, P.; Schneider, J.; Li, F.; Zhao, W.; Patel, U.; Castellano, F. N.;
Eisenberg, R. J. Am. Chem. Soc. 2008, 130, 5056–5058. (b) Du, P.; Knowles,
K.; Eisenberg, R. J. Am. Chem. Soc. 2008, 130, 12576–12577. (c) Zhang, D.;
Wu, L.-Z.; Zhou, L.; Han, X.; Yang, Q.-Z.; Zhang, L.-P.; Tung, C.-H. J. Am.
Chem. Soc. 2004, 126, 3440–3441. (d) Han, X.; Wu, L. Z.; Si, G.; Pan, J.; Yang,
Q. Z.; Zhang, L. P.; Tung, C. H. Chem.;Eur. J. 2007, 13, 1231–1239. (e)
Okazaki, R.; Masaoka, S.; Sakai, K. Dalton Trans. 2009, 6127–6133.
(6) (a) Lu, W.; Mi, B. X.; Chan, M. C. W.; Hui, Z.; Che, C. M.; Zhu, N.
Y.; Lee, S. T. J. Am. Chem. Soc. 2004, 126, 4958–4971. (b) Yu, C.; Chan,
K. H.-Y.; Wong, K. M.-C.; Yam, V. W.-W. Chem.;Eur. J. 2008, 14, 4577–4584.
(2) (a) Yam, V. W.-W.; Tang, R. P.-L.; Wong, K. M.-C.; Cheung, K.-K.
Organometallics 2001, 20, 4476–4482. (b) Zhang, H.; Zhang, B.; Li, Y.; Sun, W.
Inorg. Chem. 2009, 48, 3617–3627. (c) Muro, M. L.; Castellano, F. N. Dalton
Trans. 2007, 4659–4665. (d) Tam, A. Y.-Y.; Lam, W. H.; Wong, K. M.-C.; Zhu,
N.; Yam, V. W.-W. Chem.;Eur. J. 2008, 14, 4562–4576. (e) Wang, K.; Haga,
M.-a.; Monjushiro, H.; Akiba, M.; Sasaki, Y. Inorg. Chem. 2000, 39, 4022–4028.
(f) Willison, S. A.; Jude, H.; Antonelli, R. M.; Rennekamp, J. M.; Eckert, N. A.;
Bauer, J. A. K.; Connick, W. B. Inorg. Chem. 2004, 43, 2548–2555.
(3) (a) Zhou, X.; Zhang, H.-X.; Pan, Q.-J.; Xia, B.-H.; Tang, A.-C. J.
Phys. Chem. A 2005, 109, 8809–8818. (b) Zhou, X.; Pan, Q.-J.; Liu, T.; Li, M.-
X.; Zhang, H.-X. THEOCHEM 2008, 863, 91–98. (c) Moore, J. J.; Nash, J. J.;
Fanwick, P. E.; McMillin, D. R. Inorg. Chem. 2002, 41, 6387–6396. (d) Shi, L.
L.; Li, T.; Zhao, S. S.; Li, H.; Su, Z. Theor. Chem. Acc. 2009, 124, 29–36.
r
pubs.acs.org/IC
Published on Web 01/27/2010
2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 5, 2010 2211
various morphologies7 and vapor-induced luminescence
changes,8 as well as intriguing spectroscopic and lumine-
scence properties in both monomers and aggregates.9 Various
types of tridentate chelating ligands with N∧N∧N,10 N∧N∧C,4c,11
C∧N∧C,12 or N∧C∧N13 donors have been used to synthesize
planar platinum(II) complexes.
The 3-bis(2-pyridylimino)isoindoline (BPI) derivatives
have been investigated regarding their coordination chemis-
try to transition-metal ions,14-17 in which they behave mostly
as monoanionic N∧N∧N tridentate ligands. A series of
platinum(II) and palladium(II) complexes with BPI ligands
have been synthesized, and some of them show catalytic
properties.16,17 The X-ray crystallographic studies on
palladium(II)16,17 and platinum(II) complexes17a with BPI
ligands show that the geometry around the platinum(II)
center is closer to that of the ideal square-planar structure
with better molecular rigidity than platinum(II) complexes
with other tridentate N∧N∧N ligands.10
To our knowledge, comprehensive studies on the spectro-
scopic and photophysical properties concerning planar
platinum(II) complexes with BPI derivatives have been un-
explored. We describe herein a systematic study on the
synthesis, characterization, and spectroscopic and photophy-
sical properties of square-planar platinum(II) complexes
with 3-bis(2-pyridylimino)isoindoline (HL1), 1,3-bis(2-pyridyl-
imino)benz( f)isoindoline (HL2), or 5,6-dihydro-2,3-diphenyl-
5-(pyridin-2-ylimino)pyrrolo[3,4-b]pyrazin-7-ylidene)pyridin-
2-amine (HL3).
Experimental Section
General Procedures and Materials. All manipulations were
performed under an argon atmosphere using standard Schlenk
techniques and vacuum-line systems. Solvents were dried by
standard methods and distilled prior to use except for those of
spectroscopic grade for spectroscopic measurements. [(4-Methoxy-
phenyl)ethynyl]trimethylsilane (Me3SiCtCC6H4OMe-4), [(4-
nitrophenyl)ethynyl]trimethylsilane (Me3SiCtCC6H4NO2-4),
and [[4-(trifluoromethyl)phenyl]ethynyl]trimethylsilane (Me3-
SiCtCC6H4F-4) were synthesized by Sonogashira coupling
reactions.18 1,3-Bis(2-pyridylimino)isoindoline (HL1),17a 2,3-
dicyanonaphthalene,19a 1,3-diiminobenz(f)isoindoline,19b 2,3-
It is expected that radiationless decay can be highly
constrained because of better square-planar structures in
the platinum(II) complexes with 3-bis(2-pyridylimino)iso-
indoline derivatives, thus increasing the emissive efficiency.
20
dicyano-5,6-diphenylpyrazine,19c and Pt(tht)2Cl2 were pre-
pared according to literature procedures. Pt(L1)Cl (1) was
prepared by modification of the literature method.17a Other
chemicals were commercially available and used as received.
1,3-Bis(2-pyridylimino)benz(f)isoindoline (HL2). A mixture of
1,3-diiminobenz(f)isoindoline (500 mg, 2.56 mmol), 2-amino-
pyridine (506 mg, 5.38 mmol), and CaCl2 (28 mg, 0.25 mmol) in
1-butanol (20 mL) was refluxed for 1 day. After cooling to room
temperature, the resulting yellow precipitate was filtered off,
washed with hexane, and dried in vacuo. The crude product was
purified by chromatography on a silica gel column using di-
chloromethane/acetone (100:1) as the eluent. Yield: 60%. ESI-
MS: m/z (%) 350.0 (100) [M þ 1]þ. 1H NMR (CDCl3): δ 14.36
(1H, s, N-H), 8.64 (2H, d, J = 5.0 Hz, pyridine H-6), 8.63 (2H,
s, naphthalene), 8.05-8.07 (2H, m, naphthalene), 7.79 (2H, t,
J = 7.7 Hz, pyridine H-4), 7.61-7.64 (2H, m, naphthalene),
7.50 (2H, J = 8.0 Hz, pyridine H-3), 7.12-7.15 (2H, m, pyridine
H-5).
(7) Field, J. S.; Ledwaba, L. P.; Munro, O. Q.; McMillin, D. R.
CrystEngComm 2008, 10, 740–747.
(8) (a) Wadas, T. J.; Wang, Q.-M.; Kim, Y.-j.; Flaschenreim, C.; Blanton,
T. N.; Eisenberg, R. J. Am. Chem. Soc. 2004, 126, 16841–16849. (b) Du, P. W.;
Schneider, J.; Brennessel, W. W.; Eisenberg, R. Inorg. Chem. 2008, 47, 69–77. (c)
Grove, L. J.; Rennekamp, J. M.; Jude, H.; Connick, W. B. J. Am. Chem. Soc.
2004, 126, 1594–1595. (d) Yam, V. W.-W.; Wong, K. M.-C.; Zhu, N. Y. J. Am.
Chem. Soc. 2002, 124, 6506–6507.
(9) (a) Lu, W.; Chan, M. C. W.; Zhu, N. Y.; Che, C. M.; Li, C. N.; Hui, Z.
J. Am. Chem. Soc. 2004, 126, 7639–7651. (b) Chan, K. H.-Y.; Lam, J. W.-Y.;
Wong, K. M.-C.; Tang, B.-Z.; Yam, V. W.-W. Chem.;Eur. J. 2009, 15, 2328–
2334.
(10) (a) Tong, W.-L.; Chan, M. C. W.; Zhu, N.; Leung, S.-K. Dalton
Trans. 2009, 4741–4746. (b) Jarosz, P.; Lotito, K.; Schneider, J.; Kumaresan, D.;
Schmehl, R.; Eisenberg, R. Inorg. Chem. 2009, 48, 2420–2428. (c) Rachford, A.
A.; Goeb, S.; Ziessel, R.; Castellano, F. N. Inorg. Chem. 2008, 47, 4348–4355. (d)
Shikhova, E.; Danilov, E. O.; Kinayyigit, S.; Pomestchenko, I. E.; Tregubov, A.
D.; Camerel, F.; Retailleau, P.; Ziessel, R.; Castellano, F. N. Inorg. Chem. 2007,
46, 3038–3048. (e) Field, J. S.; Haines, R. J.; Ledwaba, L. P.; McGuire, R.; Munro,
O. Q.; Low, M. R.; McMillin, D. R. Dalton Trans. 2007, 192–199.
(11) (a) Lai, S.-W.; Lam, H.-W.; Lu, W.; Cheung, K.-K.; Che, C.-M.
Organometallics 2002, 21, 226–234. (b) Clark, M. L.; Diring, S.; Retailleau, P.;
McMillin, D. R.; Ziessel, R. Chem.;Eur. J. 2008, 24, 7168–7179. (c) Lai, S.-W.;
Chan, M. C.-W.; Cheung, T.-C.; Peng, S.-M.; Che, C.-M. Inorg. Chem. 1999, 38,
4046–4055.
5,6-Dihydro-2,3-diphenyl-5-(pyridin-2-ylimino)pyrrolo[3,4-b]-
pyrazin-7-ylidene)pyridin-2-amine (HL3). This compound was
synthesized by synthetic procedures similar to those of HL1.17a
A mixture of 2,3-dicyano-5,6-diphenylpyrazine (2 g, 7.08 mol),
2-aminopyridine (1.4 g, 14.88 mol), and CaCl2 (78.6 mg, 0.71
mmol) in 1-butanol (50 mL) was refluxed for 1 day. After
cooling to room temperature, the resulting yellow precipitate
was filtered off, washed with hexane, and dried in vacuo. The
green crude product was purified by chromatography on a silica
gel column using dichloromethane/methanol (200:1) as the
eluent. Yield: 53%. ESI-MS: m/z (%) 454.1 (100) [M þ 1]þ.
1H NMR (CDCl3): δ 14.52 (1H, s, N-H), 8.69 (2H, dd, J 1 = 4.9
Hz, J2 = 1.3 Hz, pyridine H-6), 7.82 (2H, t, J 1 = 7.7 Hz, J2 =
2.0 Hz, pyridine H-4), 7.69 (2H, d, J = 8.0 Hz, pyridine H-3),
7.59 (4H, dd, J 1 = 7.9 Hz, J2 = 1.6 Hz, Ph), 7.30-7.37 (6H, m,
(12) (a) Yam, V. W.-W.; Tang, R. P.-L.; Wong, K. M.-C.; Lu, X.-X.;
Cheung, K.-K.; Zhu, N. Chem.;Eur. J. 2008, 14, 4066–4076. (b) Berenguer,
J. R.; Lalinde, E.; Torroba, J. Inorg. Chem. 2007, 46, 9919–9930. (c) Camerel, F.;
Ziessel, R.; Donnio, B.; Bourgogne, C.; Guillon, D.; Schmutz, M.; Iacovita, C.;
Bucher, J. P. Angew. Chem., Int. Ed. 2007, 46, 2659–2662.
(13) (a) Williams, J. A. G. Chem. Soc. Rev. 2009, 38, 1783–1801. (b)
Develay, S.; Williams, J. A. G. Dalton Trans. 2008, 4562–4564. (c) Lu, W.; Law,
Y.-C.; Han, J.; Chui, S. S.-Y.; Ma, D.-L.; Zhu, N.-Y.; Che, C.-M. Chem. Asian J.
2008, 3, 59–69.
(14) Dietrich, B. L.; Egbert, J.; Morris, A. M.; Wicholas, M.; Anderson,
O. P.; Miller, S. M. Inorg. Chem. 2005, 44, 6476–6481.
(15) (a) Anderson, O. P.; la Cour, A.; Dodd, A.; Garrett, A. D.; Wicholas,
M. Inorg. Chem. 2003, 42, 122–127. (b) Wicholas, M.; Garrett, A. D.; Gleaves,
M.; Morris, A. M.; Rehm, M.; Anderson, O. P.; la Cour, A. Inorg. Chem. 2006,
45, 5804–5811.
Ph and pyridine H-5), 7.18-7.21 (2H, dd, J = 7.3 Hz, J2 =
1
4.9 Hz, Ph).
€
(16) (a) Broring, M.; Kleeberg, C. Dalton Trans. 2007, 1101–1103. (b)
€
Broring, M.; Kleeberg, C.; Tejero, E. C. Eur. J. Inorg. Chem. 2007, 3208–3216.
(18) Takahashi, S. K. Y.; Sonogashira, K.; Hagihara, N. Synthesis 1980,
627–630.
(c) Broring, M.; Kleeberg, C.; Kohler, S. Inorg. Chem. 2008, 47, 6404–6412. (d)
€
Broring, M.; Kleeberg, C. Z. Anorg. Allg. Chem. 2007, 633, 2210–2216.
(19) (a) Baird, D. M.; Maehlmann, W. P.; Bereman, R. D.; Singh, P. J.
Coord. Chem. 1997, 42, 107–126. (b) Wheeler, B. L.; Nagasubramanian, G.;
Bard, A. J.; Schechtman, L. A.; Kenney, M. E. J. Am. Chem. Soc. 1984, 106,
7404–7410. (c) Cristiano, R.; Westphal, E.; Bechtold, I. H.; Bortoluzzi, A. J.;
Gallardo, H. Tetrahedron 2007, 63, 2851–2858.
(17) (a) Meder, M.; Galka, C. H.; Gade, L. H. Monatsh. Chem. 2005, 136,
1693–1706. (b) Siggelkow, B.; Meder, M. B.; Galka, C. H.; Gade, L. H. Eur. J.
Inorg. Chem. 2004, 3424–3435. (c) Meder, M. B.; Gade, L. H. Eur. J. Inorg.
Chem. 2004, 2716–2722. (d) Langlotz, B. K.; Wadepohl, H.; Gade, L. H. Angew.
Chem., Int. Ed. 2008, 47, 4670–4674. (e) Schilf, W. J. Mol. Struct. 2004, 691,
141–148.
ꢀ
ꢀ
ꢀ
´
nez, F.; Tomas, M. J. Chem. Soc., Dalton
(20) Uson, R.; Fornies, J.; Martı
Trans. 1980, 888–894.

2212 Inorganic Chemistry, Vol. 49, No. 5, 2010
Wen et al.
Pt(L2)Cl (2). A mixture of Pt(tht)2Cl2 (200 mg, 0.45 mmol),
HL2 (158 mg, 0.45 mmol), and triethylamine (0.13 mL, 0.9
mmol) in 20 mL of methanol was refluxed for 12 h. After cooling
to room temperature, the resulting red precipitate was filtered
off, washed with water, a small amount of ethanol, and Et2O,
and dried in vacuo. The product was purified by recrystalliza-
tion from dichloromethane/n-hexane. Yield: 80%. Anal. Calcd
reduced pressure to give a solid residue. The crude product was
purified by chromatography on a silica gel column using di-
chloromethane as the eluent. Yield: 70%. Anal. Calcd for
C26H16N6O2Pt 3CH2Cl2: C, 38.95; H, 2.48; N, 9.40. Found:
3
C, 39.18; H, 2.50; N, 9.81. ESI-MS: m/z (%): 640.0 (100)
[M þ 1]þ. 1H NMR (CDCl3): δ 10.58 (2H, d, J = 6.5 Hz,
pyridine H-6), 8.22 (2H, d, J = 8.8 Hz, C6H4NO2-4), 8.12-8.14
(2H, m, Ph-L1), 7.98 (2H, t, J = 8.4 Hz, pyridine H-4), 7.75
(2H, d, J = 8.2 Hz, pyridine H-3), 7.67-7.71 (2H, m, Ph-L1),
7.59 (2H, d, J = 8.8 Hz, pyridine H-5), 7.00 (2H, t, J = 6.7 Hz,
C6H4NO2-4). IR (KBr disk, ν/cm-1): 2111s (CtC).
for C22H14N5ClPt 1/4C6H14: C, 47.01; H, 2.94; N, 11.66.
3
Found: C, 46.61; H, 2.83; N, 11.74. ESI-MS: m/z (%) 579.3
(100) [M þ 1]þ. 1H NMR (DMSO): δ 10.27 (2H, d, J = 6.4 Hz,
pyridine H-6), 8.54 (2H, s, naphthalene), 8.04-8.06 (2H, m,
naphthalene), 7.91 (2H, t, J = 7.5 Hz, pyridine H-4), 7.58-7.61
(2H, m, naphthalene), 7.61 (2H, d, J = 7.5 Hz, pyridine H-3),
7.02 (2H, t, J = 6.9 Hz, pyridine H-5).
Pt(L1)(CtCC6H4OCH3-4) (8). This compound was pre-
pared by the same synthetic procedure as that of 7 except that
[(4-methoxyphenyl)ethynyl]trimethylsilane was used in place of
[(4-nitrophenyl)ethynyl]trimethylsilane. Yield: 80%. Anal.
Calcd for C27H19N5OPt: C, 51.92; H, 3.07; N, 11.21. Found:
C, 52.35; H, 3.16; N, 10.89. ESI-MS: m/z (%) 625.0 (100) [M þ
Pt(L3)Cl (3). This compound was prepared by the same
synthetic procedure as that of 2 except that HL3 was used in
place of HL2. Yield: 65%. Anal. Calcd for C28H18N7ClPt: C,
49.24; H, 2.66; N, 14.35. Found: C, 49.18; H, 2.67; N, 14.28. ESI-
MS: m/z (%) 683.2 (100) [M þ 1]þ. 1H NMR (CDCl3): δ 10.39
(2H, dd, J1 = 6.5 Hz, J2 = 1.5 Hz, pyridine H-6), 8.01 (2H, td,
J1 = 7.6 Hz, J2 = 1.6 Hz, pyridine H-4), 7.88 (2H, dd, J1 = 8.1
Hz, J2 = 1.5 Hz, pyridine H-3), 7.59-7.62 (4H, m, Ph-L3),
7.32-7.39 (6H, m, Ph, pyridine H-5), 7.15 (2H, td, J1 = 5.8 Hz,
J2 = 1.8 Hz, Ph).
1
1]þ. H NMR (CDCl3): δ 10.81 (2H, d, J = 6.4 Hz, pyridine
H-6), 8.08-8.09 (2H, m, Ph-L1), 7.93 (2H, t, J = 7.8 Hz,
pyridine H-4), 7.68 (2H, d, J = 8.2 Hz, pyridine H-3), 7.63-7.65
(2H, m, Ph-L1), 7.46 (2H, d, J = 8.8 Hz, pyridine H-5), 6.96 (2H,
t, J = 6.4 Hz, C6H4OCH3-4), 6.88 (2H, d, J = 8.6 Hz, C6H4OCH3-
4), 3.83 (s, 3H, OCH3). IR (KBr disk, ν/cm-1): 2115s (CtC).
Pt(L1)(CtCC6H4CF3-4) (9). This compound was prepared
by the same synthetic procedure as that of 7 except that
[[4-(trifluoromethyl)phenyl]ethynyl]trimethylsilane was used in
place of [(4-nitrophenyl)ethynyl]trimethylsilane. Yield: 80%.
Anal. Calcd for C27H16F3N5Pt: C, 48.95; H, 2.43; N, 10.57.
Found: C, 48.90; H, 2.45; N, 10.68. ESI-MS: m/z (%) 664.0 (100)
[M þ 1]þ. 1H NMR (CDCl3): δ 10.63 (2H, d, J = 5.8 Hz,
pyridine H-6), 8.07-8.09 (2H, m, Ph-L1), 7.93 (2H, t, J = 7.0
Hz, pyridine H-4), 7.68 (2H, d, J = 8.4 Hz, pyridine H-3),
7.64-7.69 (2H, m, Ph-L1), 7.57 (4H, m, pyridine H-5, C6H4-
OCF3-4), 6.94 (2H, t, J = 5.1 Hz, C6H4OCF3-4). IR (KBr disk,
ν/cm-1): 2111s (CtC).
Pt(L1)(CtCC6H5) (4). A mixture of 1 (100 mg, 0.19 mmol),
phenylacetylene (0.086 mL, 0.80 mmol), CuI (10 mg, 0.05
mmol), and NEt3 (5 mL) in dichloromethane (30 mL) was
refluxed for 12 h. After cooling to room temperature, the
reaction mixture was filtered and the filtrate was evaporated
to dryness under reduced pressure to give a solid residue. The
crude product was purified by chromatography on a silica gel
column using dichloromethane as the eluent. Yield: 68%. Anal.
Calcd for C26H17N5Pt: C, 52.53; H, 2.88; N, 11.78. Found: C,
52.32; H, 2.63; N, 11.62. ESI-MS: m/z (%) 595.4 (100) [M þ 1]þ.
1H NMR (CDCl3): δ 10.78 (2H, d, J = 5.4 Hz, pyridine H-6),
8.09-8.11 (2H, m, Ph-L1), 7.93 (2H, t, J = 6.9 Hz, pyridine H-
4), 7.69 (2H, d, J = 8.0 Hz, pyridine H-3), 7.64-7.66 (2H, m,
Ph-L1), 7.54 (2H, d, J = 7.2 Hz, pyridine H-5), 7.33 (2H, t, J =
7.5 Hz, C6H5), 7.23-7.26 (1H, m, C6H5), 6.96 (2H, t, J = 6.7 Hz,
C6H5). IR (KBr disk, ν/cm-1): 2113s (CtC).
Pt(L2)(CtCC6H4But-4) (10). This compound was prepared
by the same synthetic procedure as that of 4 except that 2 and
(4-tert-butylphenyl)acetylene were used in place of 1 and phe-
nylacetylene, respectively. Anal. Calcd for C34H27N5Pt 1/2CH2-
3
Cl2: C, 55.76; H, 3.80; N, 9.42. Found: C, 55.36; H, 3.75; N, 9.53.
1
ESI-MS: m/z (%) 701.6 (100) [M þ 1]þ. H NMR (CDCl3):
Pt(L1)(CtCC6H4F-4) (5). This compound was prepared
by the same synthetic procedure as that of 4, except that
(4-fluorophenyl)acetylene was used in place of phenylacetylene.
Yield: 70%. Anal. Calcd for C26H16FN5Pt: C, 50.98; H, 2.63; N,
11.43. Found: C, 50.87; H, 2.57; N, 11.52. ESI-MS: m/z (%)
613.3 (100) [M þ 1]þ. 1H NMR (CDCl3): δ 10.72 (2H, d, J = 6.4
Hz, pyridine H-6), 8.07-8.09 (2H, m, Ph-L1), 7.92 (2H, t, J =
7.5 Hz, pyridine H-4), 7.67 (2H, d, J = 8.0 Hz, pyridine H-3),
7.63-7.68 (2H, m, Ph-L1), 7.47 (2H, t, J = 5.9 Hz, pyridine
H-5), 7.01 (2H, t, J = 8.6 Hz, C6H4F-4), 6.95 (2H, t, J = 6.7 Hz,
C6H4F-4). IR (KBr disk, ν/cm-1): 2113s (CtC).
δ 10.65 (2H, d, J = 5.7 Hz, pyridine H-6), 8.66 (2H, s,
naphthalene), 8.26-8.29 (2H, m, naphthalene), 8.19 (2H, t,
J = 7.3 Hz, pyridine H-4), 7.69-7.74 (4H, m, naphthalene,
pyridine H-3), 7.34-7.39 (4H, m, pyridine H-5, C6H4But-4),
7.23 (2H, t, J = 6.2 Hz, C6H4But-4), 1.30 (9H, s, But). IR (KBr
disk, ν/cm-1): 2115s (CtC).
Pt(L3)(CtCC6H4But-4) (11). This compound was prepared
by the same synthetic procedure as that of 4 except that 3 and
(4-tert-butylphenyl)acetylene were used in place of 1 and phenyl-
acetylene, respectively. Yield: 68%. Anal. Calcd for C40H31N7Pt: C,
59.70; H, 3.88; N, 12.18. Found: C, 59.88; H, 3.79; N, 11.95. ESI-
MS: m/z (%) 805.2 (100) [M þ 1]þ. 1H NMR (DMSO): δ 10.68
(2H, s, pyridine H-6), 8.22 (2H, t, J = 7.6 Hz, pyridine H-4), 8.02
(2H, d, J = 7.6 Hz, pyridine H-3), 7.50-7.52 (4H, m, Ph, C6H4But-
4), 7.36-7.45 (10H, m, Ph, pyridine H-5), 7.28 (2H, t, J = 6.3 Hz,
C6H4But-4), 1.30 (9H, s, But). IR (KBr disk, ν/cm-1): 2118s
(CtC).
Physical Measurements. UV-vis absorption spectra were
measured on a Perkin-Elmer Lambda 25 UV-vis spectrophoto-
meter. IR spectra were recorded on a Magna 750 FT-IR
spectrophotometer with KBr pellets. Elemental analyses (C,
H, and N) were carried out on a Perkin-Elmer model 240 C
elemental analyzer. Electrospray ionization mass spectrometry
(ESI-MS) was performed on a Finnigan LCQ mass spectro-
meter using dichloromethane/methanol mixtures as mobile
phases. The cyclic voltammograms (CVs) were made with a
potentiostat/galvanostat model 263A in dichloromethane solu-
tions containing 0.1 M Bu4NPF6 as the supporting electrolyte.
Pt(L1)(CtCC6H4But-4) (6). This compound was prepared
by the same synthetic procedure as that of 4 except that (4-tert-
butylphenyl)acetylene was used in place of phenylacetylene.
Yield: 80%. Anal. Calcd for C30H25N5Pt 1/2C6H14: C, 57.14;
3
H, 4.65; N, 10.10. Found: C, 57.20; H, 4.48, N, 9.77. ESI-MS:
m/z (%) 651.0 (100) [M þ 1]þ. 1H NMR (CDCl3): δ 10.80 (2H,
J = 6.4 Hz, pyridine H-6), 8.09-8.11 (2H, m, Ph-L1), 7.93 (2H,
t, J = 8.4 Hz, pyridine H-4), 7.69 (2H, d, J = 8.1 Hz, pyridine
H-3), 7.63-7.65 (2H, m, Ph-L1), 7.49 (2H, d, J = 8.4 Hz,
pyridine H-5), 7.36 (2H, d, J = 8.4 Hz, C6H4But-4), 6.95 (2H,
t, J = 6.7 Hz, C6H4But-4), 1.35 (9H, s, But). IR (KBr disk,
ν/cm-1): 2118s (CtC).
Pt(L1)(CtCC6H4NO2-4) (7). A mixture of 1 (200 mg, 0.38
mmol), [(4-nitrophenyl)ethynyl]trimethylsilane (387 mg, 1.90
mmol), CuI (4 mg, 0.02 mmol), and KF (330 mg, 5.7 mmol) in
dichloromethane/methanol (2:1, v/v; 30 mL) was refluxed for
1 day. After cooling to room temperature, the reaction mixture
was filtered and the filtrate was evaporated to dryness under

Article
Inorganic Chemistry, Vol. 49, No. 5, 2010 2213
The CV was made at a scan rate of 100 mV s-1. Platinum and
glassy graphite were used as the counter and working electrodes,
respectively, and the potential was measured against a Ag/AgCl
reference electrode. The potential measured was always refer-
enced to the half-wave potentials of the ferrocenium/ferrocene
couple (E1/2 = 0). Emission and excitation spectra were re-
corded on a Perkin-Elmer LS55 luminescence spectrometer with
a red-sensitive photomultiplier type R928. Emission lifetimes in
solid states and degassed solutions were determined on an
Edinburgh analytical instrument (F900 fluorescence spectro-
meter) using an LED laser at 440 nm excitation. The emission
quantum yield (Φem) in a degassed dichloromethane solution
at room temperature was calculated by Φs = Φr(Br/Bs)(ns/
nr)2(Ds/Dr) using [Ru(bpy)3](PF6)2 in acetonitrile as the stan-
dard (Φem = 0.062), where the subscripts r and s denote the
reference standard and sample solution, respectively, and n, D,
and Φ are the refractive index of the solvents, the integrated
intensity, and the luminescence quantum yield, respectively. The
quantity B is calculated by B = 1 - 10-AL, where A is the
absorbance at the excitation wavelength and L is the optical
path length.
Table 1. Crystallographic Data for 3, 4, and 6
3
4
6
empirical formula
fw
space group
a, A
b, A
C28H18C6N7Pt
683.04
P1
C26H17N5Pt
594.54
P1
C30H25N5Pt
650.64
P21/c
10.854(5)
11.573(5)
20.151(10)
8.591(4)
9.782(4)
15.367(6)
74.412(16)
74.060(16)
79.089(15)
1186.7(9)
2
7.266(3)
11.643(6)
12.473(6)
89.266(13)
82.760(13)
78.324(14)
1025.0(9)
2
c, A
R, deg
β, deg
γ, deg
V, A3
Z
101.016(8)
2485(2)
4
F
calcd, g cm-3
1.911
6.058
1.926
6.870
1.739
5.676
0.710 73
293(2)
0.0390
0.0834
0.999
μ, mm-1
radiation (λ, A)
temp, K
0.710 73
293(2)
0.0537
0.1424
1.075
0.710 73
293(2)
0.0435
0.1131
1.002
R1(Fo)a
wR2(Fo
GOF
2 b
)
P
P
P
P
a R1 = |Fo - Fc|/ Fo. b wR2 = [w(Fo2 - Fc2)2]/ [w(Fo2)]1/2
.
Crystal Structural Determination. Crystals of 3, 4, and 6
suitable for X-ray diffraction studies were obtained by layering
n-hexane onto the dichloromethane solution. Data collection
was performed on a Mercury CCD diffractometer by the ω-scan
technique at room temperature using graphite-monochromated
Mo KR (λ = 0.710 73 A) radiation. The CrystalClear software
package was used for data reduction and empirical absorption
correction. The structures were solved by direct methods. The
heavy atoms were located from an E-map, and the rest of the
non-hydrogen atoms were found in subsequent Fourier maps.
All non-hydrogen atoms were refined anisotropically, while the
hydrogen atoms were generated geometrically and refined with
isotropic thermal parameters. The structures were refined on F2
by full-matrix least-squares methods using the SHELXTL-97
program package.21 The crystallographic data are summarized
in Table 1.
using the time-dependent DFT (TD-DFT) method at the same
level as that mentioned previously.25,26 The conductor-like
polarizable continuum model (CPCM)27 with dichloromethane
as the solvent was used for calculations in solution. In these
calculations, the Hay-Wadt double-ξ method with a Los
Alamos relativistic effect basis set (LANL2DZ)28 consisting of
effective core potentials was employed for the platinum(II) atom
and the 6-31G(p,d) basis set was used for the remaining atoms.
To precisely describe the molecular properties, one additional
f-type polarization function was implemented for the platinum-
(II) atom (R = 0.18)29 and chloride atom (R = 0.514).30
Results and Discussion
Preparation and Characterization. The BPI derivatives
HL1-HL3 (Scheme 1) were synthesized by the reaction
of o-dicarbonitrile or 1,3-diiminobenz(f)isoindoline (for
HL2) with 2-aminopyridine in refluxing 1-butanol, using
CaCl2 as the catalyst.16,17 The Pt(BPI)Cl complexes 1-3
(Scheme 1) were prepared by the reactions of HL1-HL3
with Pt(tht)2Cl2 in refluxing methanol using triethyl-
amine (NEt3) as the base. 1-3 were purified by recrystall-
ization from dichloromethane/n-hexane. Alkynylplatinum-
(II) complexes 4-11 (Scheme 1) were obtained from the
reactions of Pt(BPI)Cl complexes with the corresponding
alkynes in the presence of KF or NEt3 and a catalytic amount
of CuI. They were purified by chromatography on silica gel
columns. Substitution of chloride in 1-3 with a σ-bonded
acetylide ligand increases significantly the solubility of 4-11
in halohydrocarbon solvents. The deprotonated BPI deri-
vatives L1-L3 act as anionic N∧N∧N tridentate ligands to
afford neutral platinum(II) complexes 1-3 with coordi-
nated Cl or 4-11 containing σ-bonded acetylides.
Theoretical Methodology. All of the calculations were carried
out by using the Gaussian 03 program package.22 The density
functional theory (DFT)23 at the gradient-corrected correlation
functional level PBE1PBE24 was used to optimize the ground-
state geometries of the 3-bis(2-pyridylimino)isoindoline-
platinum(II) complexes 1-4 and 6, giving the best results in
terms of the structural parameters and simulations of the
UV-vis properties by comparison of different functionals
(Table S1, Supporting Information). On the basis of the
ground-state optimized geometries, 80 singlet and 6 triplet
excited states were obtained to determine the vertical excitation
energies for all of the molecules in the dichloromethane media
(21) Sheldrick, G. M. SHELXL-97, Program for the Refinement of Crystal
€
€
Structures; University of Gottingen: Gottingen, Germany, 1997.
(22) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.;
Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa,
J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,
X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich,
S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.;
Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz,
P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson,
B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, revision
C.02; Gaussian, Inc.: Wallingford, CT, 2004.
(25) Casida, M. E.; Jamorski, C.; Casida, K. C.; Salahub, D. R. J. Chem.
Phys. 1998, 108, 4439–4449.
(26) Stratmann, R. E.; Scuseria, G. E.; Frisch, M. J. J. Chem. Phys. 1998,
109, 8218–8224.
(27) (a) Barone, V.; Cossi, M. J. Phys. Chem. A 1998, 102, 1995–2001. (b)
Cossi, M.; Regar, N.; Scalmani, G.; Barone, V. J. Comput. Chem. 2003, 24, 669–
681.
(28) (a) Wadt, W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284–298. (b) Hay,
P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299–310.
€
(29) (a) Pyykko, P.; Runeberg, N.; Mendizabal, F. Chem.;Eur. J. 1997,
€
(23) Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652.
3, 1451–1457. (b) Pyykko, P.; Mendizabal, F. Chem.;Eur. J. 1997, 3, 1458–
(24) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1997, 77,
3865–3868.
1465.
€
(30) Pyykko, P.; Mendizabal, F. Inorg. Chem. 1998, 37, 3018–3025.

2214 Inorganic Chemistry, Vol. 49, No. 5, 2010
Scheme 1. Synthetic Routes to Complexes 1-11
Wen et al.
Two different morphologies were obtained in solid
states with black and red forms for 4 and 5, respectively.
Complex 4 was mainly crystallized as the black form,
whereas the red form was isolated as a minor product
(>2%) so that the amount is insufficient for spectro-
scopic characterization, but the structure of the red form
was determined by X-ray crystallography. The black
crystals of 4 are too fragile to be characterized by X-ray
crystallography. For 5, the black form was isolated by
evaporating a dichloromethane solution to dryness under
reduced pressure or layering n-hexane onto the dichloro-
methane solution, while the red powder was obtained by
the slow evaporation of tetrahydrofuran (THF) or a
dichloromethane solution of 5.
Table 2. Selected Bond Distances [A] and Angles [deg] for 3, 4, and 6
3
4
6
Pt-Cl/C19
Pt-N1
2.335(2)
2.030(6)
1.977(6)
2.047(6)
1.965(8)
2.048(7)
1.985(6)
2.044(6)
1.224(12)
1.978(5)
2.051(4)
1.995(4)
2.049(4)
1.195(7)
Pt-N3
Pt-N5
C19-C20
N1-Pt-Cl/C19
N1-Pt-N3
88.59(18)
89.9(2)
174.3(2)
172.28(17)
89.2(2)
90.8(3)
89.0(3)
175.5(2)
172.0(3)
89.8(3)
91.0(3)
173.6(8)
90.25(19)
89.33(17)
172.35(14)
89.33(17)
89.42(16)
92.19(19)
174.8(5)
N1-Pt-N5
N3-Pt-Cl/C19
N3-Pt-N5
N5-Pt-Cl/C19
Pt-C19-C20
93.01(18)
Complexes 1-11 were characterized by elemental ana-
lysis, ESI-MS spectrometry, and 1H NMR and IR spec-
troscopies and 3, 4, and 6 by X-ray crystallography.
Elemental analysis of C, H, and N coincided well with
the calculated values for all of the compounds. Positive-
ion ESI-MS of the neutral complexes showed the corre-
sponding molecular ion peak [M þ 1]þ as the principal
peaks. Strong ν(CtC) frequencies were detected at
2110-2120 cm-1 in the IR spectra of alkynylplatinum(II)
complexes 4-11.
Slow diffusion of n-hexane into dichloromethane solu-
tions of 3, 4, and 6 afforded red crystals suitable for X-ray
diffraction measurements. Selected bond distances and
angles are summarized in Table 2. ORTEP drawings of 3,
4, and 6 are depicted in Figures 1-3, respectively. A
packing diagram of 3 showing an antiparallel stacking of
planar platinum(II) moieties is given in Figure 1
(bottom).
Platinum(II) complexes 3, 4, and 6 exhibit approxi-
mately square-planar geometry composed of ClN3 do-
nors for 3 or CN3 chromophores for 4 and 6. As indicated
by the adjacent and opposite angles (Table 2) around the
platinum(II) atoms, the square-planar structures of 3, 4,
and 6 are more perfect than those of related platinum(II)
complexes with neutral tridentate N∧N∧N ligands includ-
ing 2,20:60,200-terpyridine (tpy),2a,b 2,6-bis(N-pyrazolyl)-
pyridine (bpp),2f and bis(N-alkylbenzimidazol-2-yl)pyridines
(bzimpy).2d This is readily understandable because the
square-planar geometry with two six-membered chelating
rings in 3, 4, or6induces significantly less constraint than that
with two five-membered chelating rings in platinum(II)
complexes with tridentate tpy, bpp, or bzimpy.2-10 The
Pt-CtC angle is 173.6° for 4 and 174.8° for 5, indicating
a quasi-linear connection through σ-acetylide coordination.
Of the three Pt-N bonds for the deprotonated tridentate L
ligand, the central Pt-N3 [1.977(6)-1.995(4) A] distance is
obviously shorter than those of the two outer Pt-N1
[2.030(6)-2.051(4) A] and Pt-N5 [2.044(6)-2.049(4) A]
bonds. Noticeably, the distance difference between the cen-
tral and outer Pt-N bonds is more pronounced than that in
platinum(II) complexes with neutral tridentate N∧N∧N
ligands.2-10 In striking contrast with the coplanarity between
phenylacetylide and the CN3 donor atoms in platinum(II)
terpyridyl alkynyl complexes,2a,d,f phenylacetylide forms di-
hedral angles of 89.9 and 72.0° with the platinum(II) co-
ordination plane for 4 and 6, respectively. The Pt-C and
CtC bond distances are in the normal ranges for platinum-
(II) alkynyl complexes.2a,d,f The adjacent planar platinum(II)
moieties exhibit an antiparallel packing so as to induce a
severe slide from one another, as shown in Figure 1 (bottom).
The shortest intermolecular Pt Pt separations are 4.73 A
for 3, 6.33 A for 4, and 4.73 A for 6, precluding the possibility
of metallophilic Pt-Pt interactions.
3 3 3

Article
Inorganic Chemistry, Vol. 49, No. 5, 2010 2215
Figure 3. ORTEP drawing of complex 6 with an atom-labeling scheme
showing 30% thermal ellipsoids.
Table 3. Electrochemical Data for 1-11a in a 0.1 M (Bun4N)(PF6)/Dichlor-
omethane Solutiona
complex
Eox (V)b
Ered1 (V)
Ered2 (V)
HL1c
-1.88
-2.00
-2.06
-1.86
-1.92
-1.60
-1.96
-1.97
-1.97
-1.97
-1.97
-1.96
-2.00
-1.68
HL2c
HL3c
1
2
3
4
5
6
7
8
9
10
11
-1.65
-1.55
-1.64
-1.34
-1.64
-1.63
-1.62
-1.64
-1.64
-1.62
-1.70
-1.38
0.91
0.90
1.04
0.67
0.68
0.67
0.70
0.65
0.68
0.63
0.74
Figure 1. ORTEP drawing (top) with an atom labeling scheme showing
30% thermal ellipsoids and a packing diagram (bottom) of complex 3.
a Potential data in volts vs Fcþ/Fc are from single-scan CVs recorded
at 25 °C in a 0.1 M dichloromethane/(Bu4N)(PF6) solution. b This redox
wave is irreversible, and Eox is the potential of the anodic peak. c This
redox wave is irreversible, and Ered is the potential of the cathodic peak.
Figure 2. ORTEP drawing of complex 4 with an atom-labeling scheme
showing 30% thermal ellipsoids.
Figure 4. CV of 4 in a 0.1 M dichloromethane/(Bun4N)(PF6) solution.
The scan rate is 100 mV s-1
.
Electrochemical Properties. The CVs of 1-11 in a
0.1 M (Bun N)(PF6)/dichloromethane solution displayed
As indicated in Table 3, the irreversible anodic wave of
complexes 1-11 at þ0.63 to þ1.04 V is insensitive to
variations in both L and alkynyl ligands. This suggests
that this process arises mainly from metal-centered oxida-
tion, mixed probably with some ligand-centered charac-
ter.11b This is in accordance with the observation that
the corresponding oxidation potential is obviously low-
ered in alkynylplatinum(II) complexes 4-10 (0.63-
0.74 V) compared with those in the corresponding chlor-
ide-coordinated complexes 1 (0.91 V), 2 (0.90 V), and 3
(1.04 V) because the strong-field alkynyl ligand in
alkynylplatinum(II) complexes would destabilize the
dπ(Pt) orbital, leading to lower oxidation potentials for
4-10. The higher platinum-based oxidation potential for
3 (1.04 V) than for 1 (0.91 V) and 2 (0.90 V) is due to the
4
an irreversible anodic wave at þ0.63 to þ1.04 V and two
quasi-reversible reduction waves at -1.34 to -2.06 V vs
Fcþ/Fc. The electrochemical data for complexes 1-11,
together with the free ligands HL1-HL3, are summar-
ized in Table 3. The CV of 4 in a 0.1 M (Bun N)(PF6)/
4
dichloromethane solution is depicted in Figure 4. The free
ligands HL1-HL3 display one or two irreversible reduc-
tion waves and follow the order HL2 (-2.00 V) f HL1
(-1.88 V) f HL3 (-1.65 and -2.06 V). This is in
accordance with the trend of the absorption spectra and
the highest occupied molecular orbital (HOMO)-lowest
unoccupied molecular orbital (LUMO) energy gap (vide
infra). A detailed explanation is given in the UV-Vis
Absorption Spectra section.

2216 Inorganic Chemistry, Vol. 49, No. 5, 2010
Wen et al.
Table 4. UV-Vis Absorption and Luminescence Data for 1-11 at Ambient Temperature
medium
CH2Cl2
solid
CH2Cl2
solid
λ
abs/nm (ε/dm3 mol-1 cm-1
)
λ
max/nm (τem/μs)
φem/%
1
2
3
4
5
249 (48 270), 277 (30 470), 347 (19 990), 385 (11 000), 468 (11 300), 495 (11 260)
251 (33 100), 301 (54 700), 385 (18 950), 409 (20 270), 458 (14 100), 480 (13 900)
268 (35 470), 340 (34 640), 493 (9250), 514 (8760)
631 (0.96)
636 (0.63)
601 (2.98)
602 (0.27), 648sh
668 (0.28)
602sh, 660 (0.55), 720sh
625 (0.57)
598, 760 (<0.01)
625 (0.51)
594, 747 (<0.01)
637 (0.48), 690sh
630 (0.21)
617 (0.24), 666sh
612 (2.37)
616 (0.05), 671sh
635 (0.05)
650 (0.14)
0.54
3.79
0.06
0.67
0.70
CH2Cl2
solid
CH2Cl2
solid (black)
CH2Cl2
solid (black)
solid (red)
CH2Cl2
solid
CH2Cl2
solid
CH2Cl2
solid
CH2Cl2
solid
CH2Cl2
solid
CH2Cl2
solid
251 (46870), 280 (45650), 350 (19060), 472 (8910), 493 (8910)
251 (46 870), 277 (40 300), 350 (17 480), 472 (8910), 493 (8900)
6
249 (47 400), 278 (48 300), 348 (17 470), 378 (11 600), 472 (8520), 494 (7970)
251 (37 400), 278 (23 300), 367 (30 720), 463 (9320), 489 (9490)
250 (44 200), 279 (46 870), 349 (17 600), 471 (7710), 496 (7700)
251 (46 370), 287 (43 950), 349 (19 560), 468 (10 130), 490 (10 130)
302 (61 970), 312 (59 520), 384 (21 470), 408 (21 700), 462 (10 640), 481 (10 610)
269 (43 410), 344 (35 250), 491 (6200), 515 (5780)
0.36
3.05
0.10
2.86
3.79
0.03
7
8
9
614 (1.66)
602 (0.05), 656sh
605 (1.18)
594 (0.22)
681 (0.05)
weak
10
11
electron-deficient nature of L3, making oxidation of 3
more difficult than that of 1 and 2.
Because the reduction potentials (Table 3) are depen-
dent on the L ligand but insensitive to the R substituents
on the phenyl ring in the alkynyl ligands HCtCC6H4R-4,
it is suggested that the two quasi-reversible couples
originate most likely from L ligand-based reductions.
This is supported by DFT calculations, in which the
LUMO is found to be mainly derived from the π* orbital
localized on the L ligand (vide infra). This assignment is
also in line with the observation that 1, 2, and 4-10 show
more negative reduction potentials than 3 and 11 because
the electron-deficient substituents on the L3 ligand would
decrease the π*(L3)-orbital energy, making reduc-
tion easier for 3 and 11. The reduction potentials of 1-3
are in the order of 2 (-1.64 and -1.92 V) f 1 (-1.55 and
-1.86 V) f 3 (-1.34 and -1.60 V), and those of 6, 10, and
11 with the same acetylide ligand but different tridentate
L ligands follow 10 (-1.70 and -2.00 V) f 6 (-1.62 and
-1.97 V) f 11 (-1.38 and -1.68 V). The smaller reduc-
tion potentials for 3 (or 11) than for 1 (or 6) and 2 (or 10)
result most likely from the better π-accepting capability
because of the electron-deficient character of the L3 ligand,
making 3 (or 11) receive an electron more readily. The more
negative reduction potentials for 2 (or 10) than for 1 (or 6)
canbeassignedtothefactthattheHOMO-LUMO gap is 2
(or 10) > 1 (or 6) (vide infra), making it more difficult for 2
(or 10) to receive an electron.
UV-Vis Absorption Spectra. The UV-vis absorp-
tion spectral data of 1-11 are presented in Table 4. The
electronic absorption spectra of 1-11 are featured with
high-energy bands below 300 nm, middle-energy bands at
300-380 nm, and low-energy absorption bands beyond
420 nm. As suggested from DFT calculations (vide infra),
the high-energy bands result primarily from singlet in-
traligand (1IL) transitions of the L and acetylide ligands.
The middle-energy absorption bands can be ascribed to
predominant a π f π* (L) 1IL transition, mixed with some
character from 5d(Pt) fπ*(L) singlet metal-to-ligand charge-
transfer (1MLCT) and p(Cl)/π(CtCC6H4R-4) f π* (L)
Figure 5. UV-vis absorption spectra of HL1-HL3 and 1-3 in dichlor-
omethane solutions (c = 2 ꢀ 10-5 M) at room temperature.
ligand-to-ligand charge-transfer (LLCT) states. The low-
energy bands at 420-560 nm result from π f π*(L) 1IL
1
and 5d(Pt) f π*(L) MLCT transitions mixed with a
minor contribution from the p(Cl) f π*(L) 1LLCT state
for chloride-coordinated complexes 1-3. Upon substitu-
tion of chloride with acetylide ligands in 4-11, the low-
energy absorption bands are mainly contributed by the
1IL and 1MLCT states, together with an increased char-
acter from the π(CtCC6H4R-4) f π*(L) 1LLCT state.
Figure 5 depicts the UV-vis absorption spectra of
HL1-HL3 and 1-3 in dichloromethane solutions at
ambient temperature. Compared with those in ligands
HL1-HL3 (380-410 nm), the absorption maxima of
low-energy bands in complexes 1-3 (480-520 nm) are
significantly red-shifted to a shorter-wavelength region.
This is assignable to spin-orbit coupling from the heavy-
atom effect of the platinum(II) ion as well as a 5d(Pt) f
π*(L) MLCT transition upon deprotonated L1-L3 bind-
ing to the platinum(II) ion. It is intriguing that the low-
energy absorption wavelength of the free HL ligand in the
near-UV region exhibits the order HL2 (380 and 396 nm) <
HL1 (386 and 408 nm) < HL3 (395 and 420 nm), although
HL2 is more extensively conjugated than HL1. The higher
wavelength and lower energy of absorption features for HL3

Article
Inorganic Chemistry, Vol. 49, No. 5, 2010 2217
than for HL1 and HL2 result most likely from the better
π-accepting capability because of the electron-deficient char-
acter of HL3.
Supporting Information). In contrast, the LUMOs for
HL1 and HL2 arise from π*-orbital interaction between
the pure carbon moiety and the N-containing one, in
which the π* orbitals of the two moieties have similar
orbital energies. Compared with that of the naphthylene
in HL2, the π* orbital of the phenylene in HL1 is closer in
energy to the π* orbital of the N-containing moiety. As a
result, the orbital interaction is more significant for HL1
so as to give a lower energy of the LUMO, thus leading to
a smaller HOMO-LUMO gap in HL1, as depicted in
Figure S5 (Supporting Information). Although the
naphthylene in HL2 has a larger conjugated system, the
energy match between the π* orbitals of the naphthylene
and the π* orbitals of the N-containing moiety is worse
than that in HL1 so as to give a less significant orbital
interaction, thus resulting in a higher level of the LUMO
and a larger HOMO-LUMO gap in HL2. We have to
point out that in the schematic illustration shown in
Figure S5 (Supporting Information) we purposely
aligned the π- and π*-orbital energy levels of the N-
containing moiety to fit the resulting orbital levels of
HL1 and HL2.
In the same trend as ligands L1-L3, the absorption
maxima of the low-energy bands in platinum(II) com-
plexes 1-3 (Figure 5) follow 2 (458 and 480 nm) < 1 (468
and 495 nm) < 3 (493 and 514 nm), which is in accordance
with the HOMO-LUMO gap with 2 (3.54 eV) > 1 (3.46
eV) > 3 (3.31 eV) from DFT calculations (vide infra).
Similarly, the low-energy absorption bands of 6, 10, and
11 (Figure S4, Supporting Information) with the same
acetylide ligand [(4-tert-butylphenyl)acetylide] but differ-
ent L ligands follow 10 (462 and 481 nm) < 6 (472 and
494 nm) < 11 (491 and 515 nm). Thus, the low-energy
absorption bands can be modulated to some extent by
modification of the L ligands. By a comparison of the
low-energy absorption bands in L1 complexes 4-9
containing CtC(C6H4)R-4 with different electron-do-
nating or -withdrawing substituent R, it is found that
the lowest-lying absorption bands are insensitive to the
R substituent on the phenyl ring in the alkynyl ligands
HCtCC6H4R-4 probably because of the predominant
contribution of the π f π*(L) 1IL state to the absorption
character, as revealed by DFT calculations (vide infra).
This is in contrast with that of alkynylplatinum(II) com-
plexes of tpy or bzimpy,2,10 in which low-energy absorp-
tion bands are usually tunable to some extent by the
introduction of an electron-donating or -withdrawing
substituent in the phenylacetylide ligand.
The absorption wavelength trend of HL2 (380 and 396
nm) < HL1 (386 and 408 nm) is unexpected and in drastic
contrast with the general principle that the absorption
energy is always decreased as a result of increased con-
jugation.31 Although the conjugated system of HL2 is
larger than that of HL1, the absorption energy of HL2 is
higher than that of HL1. To understand the unexpectedly
abnormal absorption trend, a DFT calculation was per-
formed for HL1 and HL2.
The conjugate system for the ligand HL can be re-
garded as consisting of two electronically very different
structural moieties, one being a pure carbon moiety
(phenylene for HL1 or naphthylene for HL2) and the
other containing N-heteroatoms (the same for HL1 and
HL2). As depicted in Figure S4 (Supporting Informa-
tion), the HOMO for HL1 or HL2 is predominantly
contributed by an N-heteroatomic moiety so that the
HOMO level of HL1 (-5.9651 eV) is close to that of
HL2 (-5.9553 eV). The LUMO, however, is resident on
both N-heteroatomic and pure carbon moieties. As in-
dicated in the diagrams of the LUMO (Figure S4, Sup-
porting Information) for HL1 and HL2, although the
naphthylene in HL2 has a more extended system than the
phenylene in HL1, the naphthylene in HL2 contributes
more antibonding π* composition so as to afford a higher
level of LUMO for HL2 (-1.9957 eV) compared with that
for HL1 (-2.0896 eV). This leads to a larger HOMO-
LUMO gap for HL2 (3.9596 eV) than that for HL1 (3.8755
eV), thus explaining the absorption trend of HL1 and HL2.
To understand this more clearly, Figure S5 (Supporting
Information) shows a proposed schematic illustration of
the relevant orbital interaction. In this schematic illustra-
tion, we made an unconventional assumption that the π
and π* orbitals of the N-containing moiety are higher in
energy than the π and π* orbitals of the pure carbon
moiety (phenylene or naphthylene). This unconventional
assumption is based on the fact that the HOMOs of HL1
and HL2 are mainly contributed by the highest π orbital
from the N-containing moiety while the LUMOs of HL1
and HL2 are significantly contributed by the lowest π*
orbital of the pure carbon moiety (phenylene or
naphthylene). Our molecular orbital calculations on
HL1 and HL2 show that the HOMO for HL1 or HL2
corresponds to the out-of-phase combination between the
π orbitals of the pure carbon moiety and the N-containing
moiety while the LUMO is the in-phase combination of
the π* orbitals of the two moieties. The π orbitals of the
N-containing moiety and the pure carbon moiety
(phenylene or naphthylene) differ significantly in their
orbital energies so that the orbital interaction between
them is less significant and the HOMOs for HL1 and HL2
are mainly contributed by π orbitals from the N-contain-
ing moiety. As a consequence, the HOMOs for both
HL1 and HL2 have similar orbital energies (Figure S5,
The UV-vis electronic spectra of 1 (Figure S6, Sup-
porting Information) and 4 (Figure S7, Supporting In-
formation) in different solutions at ambient temperature
indicate that the low-energy absorption bands exhibit a
small shift (10-20 nm) depending on the solvents. The
absorbance of the low-energy bands displays a linear
relationship with the concentration from 1 ꢀ 10-6 to
5 ꢀ 10-4 M in dichloromethane solutions. Once the solution
concentration is higher than 5 ꢀ 10-4 M, the UV-vis
absorption spectra of 1 and 4 do not obey Lambert-Beer’s
law (Figure S8, Supporting Information).
(31) (a) Vala, M.; Vynuchal, J.; Toman, P.; Weiter, M.; Lunak, S., Jr.
Dyes Pigments 2010, 84, 176–182. (b) Wasserberg, D.; Meskers, S. C. J.;
Janssen, R. A. J.; Mena-Osteritz, E.; Bauerle, P. J. Am. Chem. Soc. 2006, 128,
17007–17017. (c) Adachi, M.; Nagao, Y. Chem. Mater. 1999, 11, 2107–2114. (d)
Lee, Y. H.; Kim, Y. S. Thin Solid Films 2007, 515, 5079–5083.
Luminescence Properties. The luminescence data in-
cluding emission wavelengths, lifetimes, and quantum
yields of 1-11 are summarized in Table 4. Upon irradiation
of these complexes with near-UV light, complexes 1-11

2218 Inorganic Chemistry, Vol. 49, No. 5, 2010
Wen et al.
show bright room-temperature luminescence in both solid
states and fluid dichloromethane solutions with micro-
second or submicrosecond lifetime ranges. Large Stokes
shifts together with long emissive lifetimes reveal that they
are phosphorescent in nature with triplet excited states. In
most cases, the emission spectra in solid states at 298 K
exhibit well-resolved vibronic-structured bands (Figure S9,
Supporting Information) with vibrational progressional
spacings in the range of 1160-1460 cm-1 (Table 4), char-
acteristic of the vibrational stretching frequencies of the
aromatic CdC and CdN modes of the tridentate N-hetero-
cyclic L ligands. The emission quantum yields in degassed
dichloromethane solutions are in the range of 0.03-3.79%
at ambient temperature (Table 4). The room-temperature
emission spectra of 1 (Figure S15, Supporting Information)
in various solvents including THF, N,N-dimethylforma-
mide, toluene, CH2Cl2, and CH3CN suggest that they are
insensitive to the solution character. Upon excitation of the
dichloromethane solution of 4 at λex = 460 nm, the room-
temperature emission at 625 nm becomes stronger and
stronger with increasing concentration from 1 ꢀ 10-6 to
1 ꢀ 10-4 M. At concentrations >10-4 M, the dichloro-
methane solution of 4 (Figure S16, Supporting Informa-
tion) displays a self-quenching phenomenon, but excimeric
emission is undetectable in the range of 300-900 nm.
Nevertheless, the excitation maxima of 4 (Figure 17, Sup-
porting Information) in dichloromethane solutions at high
concentrations (>10-4 M) are gradually red-shifted from
485 nm (1 ꢀ 10-4 M) to 550 nm (1 ꢀ 10-3 M) probably
because of an increasing contribution from the π(Ct
CC6H4R-4) f π*(L) 3LLCT state.
Figure 6. Emission spectra of1 (dotted line), 2 (dashed line), and 3 (solid
line) in degassed dichloromethane solutions (c = 2 ꢀ 10-5 M) at room
temperature (λex = 460 nm).
nyl)acetylide complexes 6, 10, and11 with different L ligands,
the emission wavelength (Figure S10, Supporting In-
formation) follows 10 (615 nm) < 6 (630 nm) < 11 (681
nm) like that for the lowest-energy absorption bands. Simi-
larly, this can be reasonably interpreted by the fact that the π*
energy of L2 is enhanced whereas that of L3 is reduced
compared with that of L1. For complexes 4-9 with the same
L1 ligand but different acetylide ligands, the emission shows
some dependence on the substituent R in the acetylide ligand
CtCC6H4R-4. As depicted in Figure S14 (Supporting In-
formation), the emission of 7(612nm) withR=NO2 is blue-
shifted whereas that of 8(635nm) withR=OCH3 displays a
red shift compared with that of 4 (625 nm). Obviously, the
introduction of an electron-withdrawing substituent to the
phenylacetylide would lower the energy of the 5d(Pt) and
π(CtCC6H4R-4) orbitals, thus increasing the HOMO-
It has been demonstrated that most of the [Pt(N∧-
N∧N)Cl]þ complexes with N∧N∧N = tpy,32,33 bpp,2f or
bzimpy2d are nonemissive or weakly luminescent in fluid
solutions at ambient temperature, although they are al-
ways emissive in solid states. In striking contrast, com-
plexes 1-3 show bright luminescence with structureless
emission bands at 631, 601, and 668 nm (Figure 6),
respectively, in fluid dichloromethane solutions at 298
K, arising primarily from 3[π f π* (L)] 3IL and 3[5d(Pt) f
3
LUMO gap of the 5d(Pt) f π*(L) MLCT and π(Ct
3
CC6H4R-4) f π*(L) LLCT states. In contrast, the intro-
duction of an electron-donating substituent would reduce
the HOMO-LUMO gap of the 3MLCT and 3LLCT transi-
tions, thus inducing a red shift of the emission.
Complex 5 with (4-fluorophenyl)acetylide affords two
differently colored crystalline forms. The red form exhibits
bright-red luminescence at 637 nm (Figure S12, Supporting
Information) analogous to that measured in a fluid dichloro-
methane solution, arising most likely from the π f π*(L) 3IL
and 5d(Pt) f π*(L) 3MLCT triplet excited states mixed with
3
π*(L)] MLCT triplet excited states as revealed from
DFT calculations (vide infra). It is obvious that, com-
pared with that of 1, the emission of 2 is blue-shifted,
whereas that of 3 exhibits a red shift. The emission
wavelength 2 (601 nm) < 1 (631 nm) < 3 (668 nm) is
well consistent with that of the lowest-energy absorption
bands and the energy trend of the HOMO-LUMO gap
with 2 > 1 > 3 (vide infra). It is worth noting that the
measured emission energy 2 (2.06 eV) > 1 (1.96 eV) > 3
(1.86 eV) coincides reasonably with the calculated triplet
excitations 2 (2.16 eV) > 1 (2.06 eV) > 3 (1.93 eV) from
DFT calculations (vide infra).
3
some π(CtCC6H4R-4) f π*(L) LLCT character. The
black form, however, is weakly luminescent at 747 nm, with
a significant red shift relative to that of the red form. The
differently colored crystalline forms for a given platinum(II)
complex are likely associated with the difference in the crystal
packing in the stacking of planar platinum(II) moieties,7,8
although the crystal structures of both forms have not been
characterized by X-ray crystallography. It is likely that a
significant red shift for the black form results from a change
in the emissive character from 3MLCT to 3MMLCT
(metal-metal-to-ligand charge-transfer) state probably be-
cause of the presence of significant Pt-Pt and/or π-π
interactions in the black form.7,34-36
Upon substitution of the coordinated chloride in 1-3
with an acetylide ligand in 4-11, the emission origins
3
3
become [π f π*(L)] IL and [5d(Pt) f π*(L)] MLCT
states mixed with an enhanced contribution from the
3
π(CtCC6H4R-4) f π*(L) LLCT transition, as suggested
from DFT calculations (vide infra). For (4-tert-butylphe-
(34) Field, J. S.; Gertenbach, J. A.; Haines, R. J.; Ledwaba, L. P.;
Mashapa, N. T.; McMillin, D. R.; Munro, O. Q.; Summerton, G. C. Dalton
Trans. 2003, 1176–1180.
(32) Lai, S.-W.; Chan, M. C. W.; Cheung, K.-K.; Che, C.-M. Inorg.
Chem. 1999, 38, 4262–4267.
(33) Buchner, R.; Field, J. S.; Haines, R. J. Inorg. Chem. 1997, 36, 3952–
3956.
(35) Miskowski, V. M.; Houlding, V. H. Inorg. Chem. 1991, 30, 4446–
4452.
(36) Yam, V. W. W.; Chan, K. H. Y.; Wong, K. M. C.; Zhu, N. Y.
Chem.;Eur. J. 2005, 11, 4535–4543.
€

Article
Inorganic Chemistry, Vol. 49, No. 5, 2010 2219
Table 5. Partial Molecular Orbital Compositions (%) in the Ground State for 1 in Dichloromethane Media under TD-DFT Calculations and the Absorptions and Emission
Transitions for 1 in Dichloromethane Media Calculated by the TD-DFT Method
MO contribution (%)
orbital
energy (eV)
Pt
L1
Cl
LUMOþ1
LUMO
HOMO
HOMO-1
HOMO-3
HOMO-4
HOMO-5
-1.3576
-2.5421
-5.9993
-6.7215
-7.0138
-7.1292
-7.2826
3.1
3.7
96.8
96.3
55.6
55.4
9.5
0.1
0.0
10.4
18.3
0.9
34.0
26.4
89.5
30.6
53.1
44.5
46.4
24.9
0.5
transition
contribution (%)
E [nm (eV)]
OS
assignment
measured value (nm)
T1
S1
S4
HOMO f LUMO
HOMO f LUMO
93
91
59
37
63
15
72
601 (2.06)
466 (2.66)
358 (3.47)
0.0000
0.1312
0.2283
3IL/3MLCT/3LLCT
1IL/1MLCT/1LLCT
1IL/1MLCT/1LLCT
1MLCT
631
468, 495
380 (sh)
HOMO-1 f LUMO
HOMO-3 f LUMO
HOMO-5 f LUMO
HOMO-4 f LUMO
HOMO-4 f LUMOþ1
S8
311 (3.99)
252 (4.92)
0.1978
0.2092
1IL/1MLCT
34
1IL/1MLCT/1LLCT
1IL/1MLCT/1LLCT
S22
277
Table 6. Partial Molecular Orbital Compositions (%) in the Ground State and the Absorptions and Emission Transitions for 4 in Dichloromethane Media Calculated by the
TD-DFT Method
MO contribution (%)
orbital
energy (eV)
Pt
L1
CtCC6H5
LUMOþ3
LUMOþ1
LUMO
-0.7388
-1.2466
-2.4548
-5.8064
-5.8475
-6.4655
-7.1958
3.5
1.8
3.8
12.7
33.9
12.5
54.5
95.9
98.2
96.2
11.9
46.0
62.1
45.5
0.6
0.0
0.0
75.4
20.1
25.4
0.0
HOMO
HOMO-1
HOMO-2
HOMO-6
transition
contribution (%)
E [nm (eV)]
OS
assignment
measured value (nm)
627
T1
S1
HOMO-1 f LUMO
HOMO-2 f LUMO
HOMO-1 f LUMO
HOMO-2 f LUMO
HOMO-2 f LUMO
HOMO-6 f LUMO
HOMO-2 f LUMOþ1
HOMO-1 f LUMOþ3
84
16
94
6
95
88
68
23
600 (2.07)
0.0000
3IL/3MLCT/3LLCT
3IL/3MLCT/3LLCT
1IL/1MLCT/1LLCT
1IL/1MLCT/1LLCT
1IL/1MLCT/1LLCT
1MLCT/1ILCT
474 (2.62)
0.1047
472, 493
S3
S10
S20
370 (3.35)
310 (3.99)
275 (4.52)
0.3305
0.1657
0.4205
shoulder
350
280
1IL/1MLCT/1LLCT
1IL/1MLCT/1LLCT
Theoretical Studies. DFT calculations were carried out
for 1-4 and 6 to gain better insight into the electronic and
spectroscopic properties as well as the nature of absorp-
tion and emission origins of these platinum(II) com-
plexes. On the basis of the ground-state optimized
geometry, 80 singlet and 6 triplet excited states for the
related complexes were calculated at the PBE1PBE/
LANL2DZ[6-31G(d,p)] level with the TD-DFT, in which
the solvent effect (CH2Cl2 as the solvent) with the CPCM
approach is taken into account. The relative composi-
tions of the different energy levels in terms of the compos-
ing fragments and the absorption transition characters
are summarized in Table 5 for 1, in Table 6 for 4, and in
Tables S2-S7 (Supporting Information) for 2, 3, and 6.
Electron-density diagrams of the frontier molecular orbi-
tals involved in the absorption spectra of 1-4 and 6 in
dichloromethane are depicted in Figures S19-S23
(Supporting Information). The energy diagrams of im-
portant frontier orbitals and the single electron-density
diagrams of HOMOs and LUMOs involved in the ab-
sorptions for 1-4 and 6 are shown in Figure 7.
chelating ligand L. For 1-3, the HOMO is primarily
contributed from the platinum atom (ca. 34%) and the
chelating L ligand (55-57%), with minor contribution
from the coordinated chloride (ca. 10%). The HOMO-1
is mainly composed of the chelating ligand L with 55.4%
(Table 5), 95.3% (Table S2, Supporting Information),
and 97.3% (Table S4, Supporting Information) contribu-
tions for 1-3, respectively. In contrast to the composi-
tions of the HOMOs in 1-3, those in 4 and 6 with
acetylide ligands are quite different. The HOMO is
mainly localized on the phenylacetylide for 4 (75.4%;
Table 6) and (4-tert-butylphenyl)acetylide for 6 (69.0%)
(Table S6, Supporting Information). The HOMO-1
is resident on the platinum atom and L and acet-
ylide ligands with 33.9%, 46.0%, and 20.1% composi-
tions for 4 (Table 6) and 29.5%, 42.3%, and 28.2%
contributions for 6 (Table S6, Supporting Information),
respectively.
For chloride-containing complexes 1-3, the HOMO-
LUMO energy gap is 3.46 eV for 1, 3.54 eV for 2, and
3.31 eV for 3 (Figure 7). The calculated lowest-energy
absorption wavelength follows 449 nm (2)<466 nm (1) <
490 nm (3), well in accordance with the corresponding
Complexes 1-4 and 6 display similar LUMO features,
with the π* orbitals mainly centered on the tridentate

2220 Inorganic Chemistry, Vol. 49, No. 5, 2010
Wen et al.
Figure 7. Diagrams of the energy levels of HOMOs and LUMOs involved in the absorptions for 1-4 and 6 under TD-DFT calculations.
values from the experimental measurement (Figure 4).
The lowest-energy absorption (HOMO f LUMO) can be
primarily assigned as π f π*(L) 1IL and 5d(Pt) f π*(L)
1MLCT transitions, mixed with minor π(Cl) f π*(L)
1LLCT character. The lowest-lying triplet transitions at
601 nm for 1 (Table 5), 574 nm for 2 (Table S3, Support-
ing Information), and 643 nm for 3 (Table S5, Supporting
Information) corresponding to excitation of HOMO f
LUMO are in reasonable agreement with the experimen-
tally measured emissions (631 nm for 1, 601 nm for 2,
and 668 nm for 3) in fluid dichloromethane solutions,
typical of 3[π f π*(L)] 3IL and 3[5d(Pt) f π*(L)] 3MLCT
character, mixed with a minor contribution from the
3[π(Cl) f π*(L)] LLCT state. As a result, the emis-
3
Figure 8. Measured (solid line) and calculated (dashed line) absorption
spectra of 6 simulated with Gaussian curve. The singlet excited states
calculated are shown as vertical bars with heights equal to the oscillator
strength.
sion origins of 1-3 coincide well with the low-energy
absorption character mentioned previously. The main
singlet and triplet vertical excitation energies for each
complex from TD-DFT calculations agree well with
the experimental values (Figures S24-28, Supporting
Information).
Conclusions
As indicated in Tables 6 and S7 (Supporting Infor-
mation), the calculated lowest singlet absorptions at
474 nm for 4 (HOMO-1 f LUMO) and 492 and 463 nm
for 6 (HOMO-1 f LUMO and HOMO f LUMO)
result from an admixture of the [π f π*(L)] 1IL, [5d(Pt)
f π*(L)] 1MLCT, and [π(CtCC6H4R-4) f π*(L)]
1LLCT states. Figure 8 depicts the measured (solid line)
and calculated (dashed line) absorption spectra of 6
simulated with Gaussian curve. The triplet excitations at
600 nm for 4 (Table 6) and 603 nm for 6 (Table S7,
Supporting Information) from the HOMO-1 f LUMO
(84% for 4 and 65% for 6) transition coincide reason-
ably with the measured emissions at 625 nm for 4 and
630 nm for 6 in fluid chloromethane solutions. The
emission transitions are most likely composed of an
admixture of the 3[π f π*(L1)] 3IL, 3[5d(Pt) f π*(L1)]
3MLCT, and 3[π(CtCC6H4R-4) f π*(L1)] 3LLCT
states. By comparison with the low-energy transition
character in 1, it is found that substitution of chloride
with an acetylide ligand in 4 and 6 increases obviously
the contribution from the π(CtCC6H4R-4) f π*(L1)
LLCT state.
A series of neutral platinum(II) complexes with mono-
anionic tridentate BPI derivatives were synthesized and
characterized. As revealed from X-ray crystallography,
the platinum(II) center adopts a more perfect square-
planar geometry than that in platinum(II) terpyridine
complexes. The square-planar platinum(II) complexes
with a terminally coordinated chloride or phenylacetylide
display bright solution luminescence at ambient tempera-
ture, originating mainly from 3[π f π*(L)] 3IL and
3[5d(Pt) f π*(L)] 3MLCT triplet excited states, as verified
by DFT calculations. It is demonstrated that substitution
of a coordinated chloride in Pt(L)Cl complexes with a
phenylacetylide induces a significantly enhanced contri-
bution from the 3[π(CtCC6H4R-4) f π*(L)] 3LLCT
state. The solution luminescence can be fine-tuned by
modification of the substituents in both L and phenyl-
acetylide ligands. The low-energy absorption and emission
energy follow 2 > 1 > 3 and 10 > 6 > 11, respectively, which
coincide well with the HOMO-LUMO gap with 2 > 1 > 3
from DFT calculations and can be reasonably interpreted
by the π* energy level of the tridentate L ligands with L2 >
L1 > L3.

Article
Acknowledgment. We are thankful for financial
support from the NSFC (Grants 20625101,
20633020, 20821061, and 20931006), the 973 project
(2007CB815304) from MSTC, and the NSF of Fujian
Province (Grants 2008I0027 and 2008F3117). We are
grateful to Professor Zhenyang Lin at the Hong Kong
University of Science and Technology for his helpful
Inorganic Chemistry, Vol. 49, No. 5, 2010 2221
discussion and suggestions in the revision of this
manuscript.
Supporting Information Available: Figures giving additional
UV-vis and emission spectra, tables and figures giving DFT
calculation data, and X-ray crystallographic file in CIF format
for the structure determination of 1, 4, and 6. This material is
available free of charge via the Internet at http://pubs.acs.org.