No abstract

Perylene derivatives of N,N′-bis(2,6-diisopropylphenyl)-1,6(7)-dibromoperylene-3,4,9,10-tetracarboxylic diimide (DBrPDI) and 1,7-dibromo perylene-3,4,9,10-tetracarboxylic acid butyl ester (DBrPTE) were synthesized, and their structural and optical characterizations were explored. Both DBrPDI and DBrPTE, which were utilized as wavelength converters on a GaN/InGaN based blue LED, were singlet sensitizers and had molar absorptivity constants around 104 Lmol−1cm−1. The blue LED that was used had Commission internationale de l’eclairage (CIE) coordinates of x, y = 0.13, 0.06; power and luminous efficiencies of 2.7 lm/W and 6.6 cd/A @5 mA, respectively. Because the fluorescence quantum yield of DBrPDI was much higher than that of DBrPTE, a meaningful white light efficiency was obtained with the diimide derivative. The use of DBrPDI resulted in white light with CIE coordinates of x, y = 0.34, 0.29 and luminous efficiency of 6.35 cd/A @5 mA, respectively. Using DBrPDI in a resin matrix resulted in more than three orders of magnitude increase in the luminous efficiency value (23.0 cd/A @5 mA) while the CIE coordinates remained the same. Whenever the applied current reached 20 mA, a CRI value of Ra = 90 was obtained.

Here, we reported the photophysical studies, single-crystal X-ray crystallography, and density functional theory (DFT) calculations of two bipyridine derivative molecules. In addition, thermal gravimetric analysis and cyclic voltammetry studies were also performed for both compounds. According to crystallographic data, the π-conjugated molecules have high-quality crystal structures as a result of intramolecular and intermolecular hydrogen bonds occurring through the molecules of the compound. It was determined that when the functional groups (F– and CH3O−) were introduced to the para positions, the molecules adopted slipped stacking (J-aggregate) and antiparallel cofacial stacking (H-aggregate). It was observed that these two bipyridine derivatives disclose the relationship between molecular conformation-molecular packing modes and photophysical behavior of organic solids. The results of DFT calculations supported the structural, spectroscopic, and photophysical data and confirmed the compositions of frontier molecular orbitals in both molecules.

Amber color emitting novel Ir(III) complexes were synthesized: [Ir-(Meppy) 2 (Fpbpy)][PF 6 ] (1bPF 6 ), [Ir(Meppy) 2 (Fpbpy)][TFSI] (1bTFSI), [Ir-(Meppy) 2 (MeObpy)][PF 6 ] (2bPF 6 ) and [Ir(Meppy) 2 (MeObpy)][TFSI] (2bTFSI), where Meppy = 2-(p-methylphenyl)-pyridine (b), Fpbpy = 4,4′-bis(4-fluorophenyl)-2,2′-bipyridine(1), and MeObpy = 4,4′-bis(4-methoxy)-2,2′-bipyridine (2). The photophysical and X-ray results showed that the complexes have aggregation-induced phosphorescent emission (AIPE) and a salt-induced polymorphism effect. The highest photoluminescence intensity was observed in complex 2bTFSI compared to other complexes in the solid state. Their theoretical absorption and phosphorescence emission transitions in acetonitrile were also investigated by using double-and triple-ζ basis sets with B3LYP and PBE0 hybrid functional. The best lightemitting electrochemical cell (LEC) performance was exhibited by complex 2bTFSI, and the data obtained were as follows: Luminance, current density, luminous efficiency, turn-on time, power efficiency, and external quantum efficiency were measured as 16 156 cd/m 2 , 554 mA/ cm 2 , 8.49 cd/A, 17 s, 3.95 lm/W and 6.37%, respectively. The investigation of crystallographic characteristics have shown that the LEC performance of these complexes depends on cationic−anionic interaction which has a significant influence on molecular stacking of the molecules. Because, complex 2bTFSI, with weak cationic−anionic interactions, shows strong π•••π stacking interactions between the adjacent molecules, it is the best lighting application candidate among the complexes.

Red shift in the emission wavelength by 149 nm as a result of increased solvent polarity.