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

Porphyrin platinum (IT) 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 pi-pi 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 pi-pi 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 pi-pi interactions. The peripheral substituents hardly affected absorption and emission properties of the complexes, and the luminescent peaks at 646-656 nm were assigned to (LC)-L-3 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.