Effect of Peripheral Substituents on Luminescent Properties of the Porphyrin Platinum(Ⅱ) Complexes†

doi:10.7503/cjcu20130944

Abstract

Abstract:

Porphyrin platinum(Ⅱ) complexes with efficient red phosphorescent emission have attracted extensive interest due to their potential application in the organic light emitting diodes(OLEDs). However, the strong π-π intermolecular interactions derived from their rigid planar coordination geometry result in the occurrence of self-quenching and affect their performance. In this work, a series of porphyrin platinum(Ⅱ) complexes with different peripheral substituents(PtTEMP, PtTBMP, PtOMPP and PtDMPP) were designed, synthesized and characterized, for the purpose of effectively restraining the intermolecular π-π interaction. Single crystal X-ray structure analysis indicated that they had ideal square-planar geometry around Pt atom, and bulky t-butyl substituent could inhibit effectively π-π interactions. The peripheral substituents hardly affected absorption and emission properties of the complexes, and the luminescent peaks at 646—656 nm were assigned to ³LC phosphorescent emission. PtTBMP showed the highest emission quantum yield(0.58) and external quantum efficiency(EQE, 6.3%) due to strong steric effect of t-butyl. The luminous efficiency of PtDMPP with three methoxyl substitutents was better than PtOMPP with two methoxyl, the corresponding emission quantum yield were 0.36 and 0.29, and were 2.4% and 1.7%, respectively. The results indicated that the encapsulating effect of the peripheral substituents could improve luminescent efficiency of porphyrin platinum(Ⅱ) complexes.

Key words: Porphyrin platinum(Ⅱ) complex, Substituent, Intermolecular interaction, Hindrance effect, Electroluminescent

CLC Number:

O621.22

TrendMD:

YUAN Wei, REN Qingjiang, SUN Hengda, LI Hui, CHENG Yanxiang, MA Dongge. Effect of Peripheral Substituents on Luminescent Properties of the Porphyrin Platinum(Ⅱ) Complexes^†[J]. Chem. J. Chinese Universities, 2014, 35(6): 1229.

Figures/Tables 7

Fig.1 Molecular structures of ligands(A) and porphyrin platinum(Ⅱ) complexes(B)

Fig.2 ORTEP drawings(30% probability ellipsoids)(A, B) and packing structures(A1, B1, B2) of PtTEMP(A, A1) and H2TBMP(B, B1, B2) H atoms are omitted for clarity.

Fig.3 Normalized UV-Vis absorption(solid) and PL spectra(dash) of ligands(A) and corresponding

Table 1 Photophysical data of porphyrin ligands and corresponding platinum(Ⅱ) complexes

Compound	λ_abs/nm/lgε^a	$λ em a$ /nm	τ^b/μs	$Φ PL b, c$	10^-4 $k r d$ /s^-1	10^-4 $k nr d$ /s^-1
H₂TEMP	396/5.56; 497/4.55; 526/4.43; 568/4.32; 621/4.28	620, 689	0.017
H₂TBMP	402/5.76; 501/4.65; 534/4.48; 572/4.35; 627/4.32	626, 691	0.021
H₂OMPP	417/5.84; 512/4.57; 541/4.04; 589/4.11; 645/3.85	650, 709	0.019
H₂DMPP	420/6.07; 514/4.81; 546/4.30; 590/4.30; 646/4.04	652, 711	0.015
PtOEP	378/5.49; 500/4.17; 534/4.87	648	74	0.45	0.61	0.74
PtTEMP	380/5.74; 500/4.23; 534/4.61	646	15	0.43	2.86	3.81
PtTBMP	380/5.88; 500/4.37; 534/4.78	656	34	0.58	1.71	1.23
PtOMPP	400/5.60; 508/4.58; 540/4.69	656, 712	40	0.29	0.73	1.78
PtDMPP	404/5.65; 510/4.28; 540/4.77	654, 710	57	0.36	0.63	1.12

Table 1 Photophysical data of porphyrin ligands and corresponding platinum(Ⅱ) complexes

Compound	λ_abs/nm/lgε^a	$λ em a$ /nm	τ^b/μs	$Φ PL b, c$	10^-4 $k r d$ /s^-1	10^-4 $k nr d$ /s^-1
H₂TEMP	396/5.56; 497/4.55; 526/4.43; 568/4.32; 621/4.28	620, 689	0.017
H₂TBMP	402/5.76; 501/4.65; 534/4.48; 572/4.35; 627/4.32	626, 691	0.021
H₂OMPP	417/5.84; 512/4.57; 541/4.04; 589/4.11; 645/3.85	650, 709	0.019
H₂DMPP	420/6.07; 514/4.81; 546/4.30; 590/4.30; 646/4.04	652, 711	0.015
PtOEP	378/5.49; 500/4.17; 534/4.87	648	74	0.45	0.61	0.74
PtTEMP	380/5.74; 500/4.23; 534/4.61	646	15	0.43	2.86	3.81
PtTBMP	380/5.88; 500/4.37; 534/4.78	656	34	0.58	1.71	1.23
PtOMPP	400/5.60; 508/4.58; 540/4.69	656, 712	40	0.29	0.73	1.78
PtDMPP	404/5.65; 510/4.28; 540/4.77	654, 710	57	0.36	0.63	1.12

Table 2 EL performance of porphyrin platinum(Ⅱ) complexes(8% complexes in TCTA)*

Compound	V_on/V	B_max/(cd·m^-2)	η_c/(cd·A^-1)	η_P/(lm·W^-1)	EQE(%)	λ_max/nm	CIE(x, y)
PtOEP	4.0	271	2.14	1.98	5.8	648	(0.71, 0.28)
PtTEMP	4.2	247	1.73	1.56	4.3	648	(0.70, 0.28)
PtTBMP	4.0	412	2.21	1.98	6.3	648	(0.71, 0.28)
PtOMPP	4.3	457	0.42	0.36	1.7	665, 731	(0.65, 0.27)
PtDMPP	4.2	656	0.46	0.37	2.4	665, 733	(0.52, 0.25)

Fig.4 EL spectra(A) and EQE vs. current density(B) of the devices(8% complexes in TCTA)

Fig.5 EQE vs. doping concentration of complexes at the same current density(10 mA/cm2)

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