Structures, Electronic States, Photoluminescence, and Carrier Transport Properties of 1,1-Disubstituted 2,3,4,5-Tetraphenylsiloles

Abstract

The excellent electroluminescent (EL) properties of 1,1-disubstituted 2,3,4,5-tetraphenylsiloles, 1-methyl-1,2,3,4,5-pentaphenylsilole (MPPS), and 1,1,2,3,4,5-hexaphenylsilole (HPS) have been found. Despite some studies devoted to these materials, very little is known about the real origin of their unique EL properties. Therefore, we investigated the structures, photoluminescence (PL), and charge carrier transport properties of 1,1-disubstituted 2,3,4,5-tetraphenylsiloles as well as the effect of substituents on these characteristics. The single crystals of the three siloles involving 1,1-dimethyl-2,3,4,5-tetraphenylsilole (DMTPS), MPPS, and HPS were grown and their crystal structures were determined by X-ray diffraction. Three siloles have nonplanar molecular structures. The substituents at 1,1-positions enhance the steric hindrance and have predominant influence on the twisted degree of phenyl groups at ring carbons. This nonplanar structure reduces the intermolecular interaction and the likelihood of excimer formation, and increases PL efficiency in the solid state. The silole films show high fluorescence quantum yields (75-85%), whereas their dilute solutions exhibit a faint emission. The electronic structures of the three siloles were investigated using quantum chemical calculations. The highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs) are mainly localized on the silole ring and two phenyl groups at 2,5-positions in all cases, while the LUMOs have a significant orbital density at two exocyclic Si-C bonds. The extremely theoretical studies of luminescent properties were carried out. We calculated the nonradiative decay rate of the first excited state as well as the radiative one. It is found that the faint emission of DMTPS in solutions mainly results from the huge nonradiative decay rate. In solid states, molecular packing can remarkably restrict the intramolecular rotation of the peripheral side phenyl ring, which has a large contribution to the nonradiative transition process. This explains why the 1,1-disubstituted 2,3,4,5-tetraphenylsiloles in the thin films exhibit high fluorescence quantum yields. The charge carrier mobilities of the MPPS and HPS films were measured using a transient EL technique. We obtained a mobility of 2.1 x 10(-)(6) cm(2)/V.s in the MPPS film at an electric field of 1.2 x 10(6) V/cm. This mobility is comparable to that of Alq(3), which is one of the most extensively used electron transport materials in organic light-emitting diodes (LEDs), at the same electric field. The electron mobility of the HPS film is about approximately 1.5 times higher than that of the MPPS film. To the best of our knowledge, this kind of material is one of the most excellent emissive materials that possess both high charge carrier mobility and high PL efficiency in the solid states simultaneously. The excellent EL performances of MPPS and HPS are presumably ascribed to these characteristics.

Synthesis, structure, optoelectronic properties of novel zinc Schiff-base complexes

“…On the other hand, fluorescent complexes have been extensively studied mainly because they may be good candidates for fluorescent sensors and electroluminescent (EL) devices [9,10]. Zinc Schiff-base complexes exhibited strong electroluminescence as well as photoluminescence [1113] which are strongly coupled to molecular structures and bulk molecular packing characteristics [14,15]. Most of the zinc Schiff-base complexes may exist as either five or six-coordinated ones in their crystals.…”

Aggregation-induced emissions of tetraphenylethene derivatives and their utilities as chemical vapor sensors and in organic light-emitting diodes

“…[12][13][14][15][16] A number of AIE molecules with different structures have subsequently been developed by various research groups. [1][2][3][4][5][6][7][17][18][19][20][21] Many of these AIE dyes, however, are difficult to prepare, involving multistep reactions under stringent conditions.…”

A theoretical investigation of the two-photon absorption and fluorescent properties of coumarin-based derivatives for Pd2+ detection

“…To the best of our knowledge, the HuangRhys factors (HR) can characterize the modications of vibrational quanta (absorbed or emitted) when going from one electronic state to another, which are important for determining the K IC . 53,54 It is calculated and clearly seen from Fig. 4 that (i) in general the HR factors for R1 (with a maximum value of 3.7) are much larger than those for P 0 1 (with a maximum value of 2.8) and (ii) the C^C bond stretching modes of probe R1 appear at the 3255 cm À1 high frequency region, which further indicates that R1 has larger vibrational relaxation consumption.…”