Star-Shaped Donor-π-Acceptor Conjugated Oligomers with 1,3,5-Triazine Cores: Convergent Synthesis and Multifunctional Properties

Abstract

Monodispersed oligomers have been widely developed and used in different optoelectronic areas due to their well-defined molecular structures, high purity, and solution processability. Star-shaped oligomers are especially interesting for OLED application because of their antiaggregation abilities and stable electroluminescence. In addition, star-shaped donor-pi-acceptor conjugated molecules are known to afford good nonlinear optical and two-photon absorption properties due to the intramolecular charge transfer and cooperative enhancement effects. In this context, three generations of highly soluble 1,3,5-triazine based donor-pi-acceptor compounds, TFT1, TFT2, and TFT3, were prepared through a convergent synthetic strategy and their optoelectronic properties were fully studied, which showed distinct correlations with the structures. Closed-aperture and open-aperture Z-scan methods were employed to measure the nonlinear refractive index and two-photon absorption properties of the oligomers, respectively. TFT1 showed a high nonlinear refractive index of 4.14 x 10(-12) esu in THF solution with an excitation wavelength of 800 nm. Also, TFT1 exhibited a large two-photon absorption cross section of 234 GM and a frequency up-converted two-photon excited fluorescence with a lambda(TPEF)(max) value of 527 nm under 800 nm laser irradiation with a pulse duration of 140 fs. OLED devices using the spin-coated films of these oligomers as an active layer showed intensive blue electroluminescence with a maximum luminance of 3093 cd/m(2) at a current efficiency of 1.47 cd/A from TFT1.

Synthesis and luminescent properties of star-burst D-π-A compounds based on 1,3,5-triazine core and carbazole end-capped phenylene ethynylene arms

“…Triazine core compounds have attracted a great deal of interest in recent years due to their intriguing photophysical properties and versatile applications in organic light-emitting diodes (OLED) [1][2][3][4], organic photovoltaic cells (OPV) [5][6][7][8], thin film transistors (TFT) [9,10] and nonlinear optics [11][12][13][14]. As a unique building-block, 1,3,5-triazine (TRZ) becomes a focus due to its strong electron-accepting ability, high symmetry and easy modification.…”

“…The connections of aromatic rings at the 2, 4, and 6 positions of TRZ will not create the steric interactions of the ortho-hydrogens. Consequently, introducing a TRZ unit into the backbone, especially the central core of the star-burst conjugated molecules can not only improve the abilities of electron-injection and electron-transportation of the molecules, but also enhance their thermal stability [9].…”

“…The donor-π-acceptor (D-π-A) configuration produces a strong photo-induced charge separation in the excited state, and strong solvatochromism in the emission spectra. Fang and Wong's groups [2,3,9] reported the performance of OLED devices based on TRZ derivatives respectively, which indicated that introducing electron-donating groups and extending π-conjugated were facile methodologies to improve the optoelectronic properties of the TRZ molecules. Rogers and co-workers [12][13][14] also reported the photophysical properties of fluorene-based D-π-A or A-π-A molecules with TRZ center cores, which exhibit effective excited-state absorption and two-photon absorption (TPA) in the visible region.…”

Synthesis and Characterization of Fluorene-Based Polymers Having Azine Unit for Blue Light Emission

“…However, to develop stable pure blue polymeric emitters with their color coordinates in the Commission Internationale de L'Eclairage (CIE) chromaticity diagram within the standard blue (CIE: x< 0.15; y< 0.1) are still rare since the large energy bandgap (E g ) of these materials makes the achievement of high efficiency and a good charge balance difficult [11]. In this framework, the rational design of p-type conjugated polymers by incorporating electron-withdrawing groups, such as azine unit, seems to be a straightforward strategy to tune carrier injection and transporting properties of known materials [12]. A new donor-acceptor (D-A) system has been designed, which is expected to lower both the energy level of the highest occupied molecular orbital (E HOMO ) and energy level of the lowest unoccupied molecular orbital (E LUMO ), giving rise to a series of intriguing properties such as improved resistance to oxidation, facilitated electron injection, and ambipolar characteristics, which could simplify device fabrication and operation.…”

“…Herein, the fluorene sequences were selected as D for the reason of good thermal and electrochemical stability, high fluorescence yield and facile chemical functionalization [13,14], while 1,2,4,5-tetrazine (tetrAz) and 1,3,5-triazine (triAz) were chosen as A for their electron deficiency [12]. …”