Two small molecular cathode interlayer (CIL) materials with pyridinium ion or quaternary ammonium ion terminated 1,2,3-trihexyloxybenzene as pendant polar groups and anthrathiadiazole-4,11-dione (ATD) as a conjugated backbone, namely PBATD and TBATD, were synthesized for PCDTBT:PC71BM (PCDTBT:poly[poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)]]; PC71BM:[6,6]-phenyl C71-butyric acid methyl ester) based polymer solar cells (PSCs). A dramatic improvement in the device performance was observed when the CILs were inserted between the active layer and the Al electrode. Especially, the device modified by quaternary ammonium ion terminated TBATD exhibits a power conversion efficiency (PCE) of 7.26%, which was 1.4 times that of the device with bare Al as the cathode, due to the simultaneously enhanced open-circuit voltage (Voc), short-circuit current density (Jsc) and fill factor (FF). Importantly, the Voc (0.93 V) achieved for the TBATD modified device was among the top values that used the same kind of active layer in conventional single-junction PSCs so far. It demonstrated that the CILs presented in this study may be a promising candidate for applications in high performance PSCs.

Two phenanthro[9,10-d]imidazole (PI) derivatives, 9-N,N-diphenyl-amino-10-(4-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)phenyl)anthracene (DPAA-PPI) and 9-N,N-dipheny-amino-10-(4-(1-(4-tert-butylphenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)phenyl)anthracene (tBuDPAA-PPI), have been designed and synthesized. The two compounds exhibited high photoluminescence quantum yields (at around 0.80) in the solid state and bipolar carrier transport properties. The non-doped OLEDs using DPAA-PPI and tBuDPAA-PPI as emitting layers showed the maximum power efficiencies (PEs) of 13.9 lm W−1 and 11.4 lm W−1, corresponding to the maximum external quantum efficiencies (EQEs) of 5.2% and 4.1%, respectively. The DPAA-PPI-based OLED exhibited an extremely low turn-on voltage of 2.4 V and its luminescence reached 100, 1000, 10000 and over 100000 cd m−2 under driving voltages of 2.8, 3.6, 5.1 and 7.5 V, respectively.

A beryllium complex, Be(FBTZ)2 (HFBTZ: 2-(benzo[d]thiazol-2-yl)-5-fluorophenol), has been synthesized with the aim of developing electron transport materials (ETMs) for phosphorescent organic light-emitting diodes (PhOLEDs). The complex exhibits a high triplet energy of 2.62 eV which is able to confine triplet excitons of green or lower-energy emissive phosphorescent emitters within the emitting layer. Moreover, it possesses a low-lying LUMO energy level (−3.14 eV) allowing efficient electron injection and a high election mobility of 1.8–1.1 × 10−4 cm2 V−1 s−1 for efficient electron transport. These characters enable Be(FBTZ)2 to act as an excellent ETM in PhOLEDs. By using the complex as an electron transport layer (ETL), structurally simple green, yellow and red PhOLEDs exhibiting extremely low turn-on voltages (Von) of 2.3, 2.1 and 2.2 V and high power efficiencies (PE) up to 65.0, 84.9 and 23.1 lm W−1, respectively, have been successfully fabricated. Be(FBTZ)2 can also work as a host material for PhOLEDs as demonstrated by a green device with a maximum PE of 42.8 lm W−1 and a Von value of 2.3 V.

Acenaphtho[1,2-k]fluoranthene derivatives DPAF-n as new building blocks for one-dimensional (1D) structure assembly have been developed and employed to fabricate luminescent twisted nano/micro-wires; and the DPAF rigid core attached via flexible alkyl chains with suitable lengths is critical for the formation of twisted architectures.

Two novel four-coordinate boron-containing emitters 1 and 2 with deep-blue emissions were synthesized by refluxing a 2-(2-hydroxyphenyl)benzimidazole ligand with triphenylborane or bromodibenzoborole. The boron chelation produced a new π-conjugated skeleton, which rendered the synthesized boron materials with intense fluorescence, good thermal stability, and high carrier mobility. Both compounds displayed deep-blue emissions in solutions with very high fluorescence quantum yields (over 0.70). More importantly, the samples showed identical fluorescence in the solution and solid states, and the efficiency was maintained at a high level (approximately 0.50) because of the bulky substituents between the boron atom and the benzimidazole unit, which can effectively separate the flat luminescent units. In addition, neat thin films composed of 1 or 2 exhibited high electron and hole mobility in the same order of magnitude 10–4, as determined by time-of-flight. The fabricated electroluminescent devices that employed 1 or 2 as emitting materials showed high-performance deep-blue emissions with Commission Internationale de L’Eclairage (CIE) coordinates of (X = 0.15, Y = 0.09) and (X = 0.16, Y = 0.08), respectively. Thus, the synthesized boron-containing materials are ideal candidates for fabricating high-performance deep-blue organic light-emitting diodes.

Highly efficient phosphorescent organic light-emitting diodes (PhOLEDs) based on two iridium complexes constructed by the N^C^N-coordinated terdentate ligands (also called pincer ligands) have been achieved. They exhibit high peak power efficiency (PE) and external quantum efficiency (EQE) values of 35.5 lm W−1 & 15.8% for blue-green emission, 47.4 lm W−1 & 16.7% for green emission, which maintain the high levels of 19.2 lm W−1 & 14.5% and 30.6 lm W−1 & 16.1% at rather high and practical luminance of 500 cd m−2 with low driving voltages of less than 6 V. These values show almost a twofold enhancement over the most efficient PhOLEDs based on pincer iridium complexes ever reported. Here, the appropriate selection of a prominent electron-transport molecule TPBi as a host to match the dopant molecules (1 or 2) that possess sufficient hole-transport ability is critical in the remarkable EL-performance improvement compared to previous reports. We will present a comprehensive investigation that not only encompasses the conventional thermal, photophysical and electrochemical properties of both complexes, but also emphatically studies the charge carrier injecting/transporting and electroluminescent (EL) characteristics of two phosphorescent emitters doped in different hosts.

Three alcohol/water-soluble porphyrins (Zn-TPyPMeI:zinc(II) meso-tetra(N-methyl-4-pyridyl) porphyrin tetra-iodide, Zn-TPyPAdBr:zinc(II) meso-tetra[1-(1-adamantylmethyl ketone)-4-pyridyl] porphyrin tetra-bromide and MnCl-TPyPAdBr:man-ganese(III) meso-tetra[1-(1-adamantylmethyl ketone)-4-pyridyl] porphyrin tetra-bromide were employed as cathode interlayers to fabricate polymer solar cells (PSCs). The PC71BM ([6,6]-phenyl C71 butyric acid methyl ester) and PCDTBT (poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)])-blend films were used as active layers in polymer solar cells (PSCs). The PSCs with alcohol/water-soluble porphyrins interlayer showed obviously higher power conversion efficiency (PCE) than those without interlayers. The highest PCE, 6.86%, was achieved for the device with MnCl-TPyPAdBr as an interlayer. Ultraviolet photoemission spectroscopic (UPS), carrier mobility, atomic force microscopy (AFM) and contact angle (θ) characterizations demonstrated that the porphyrin molecules can result in the formation of interfacial dipole layer between active layer and cathode. The interfacial dipole layer can obviously improve the open-circuit voltage (Voc) and charge extraction, and sequentially lead to the increase of PCE.

The structures and properties of an indole-ring-fused quinacridone derivative 5,8,15,18-tetraoctyl-5,8,15,18-tetrahydroindolo[3,2-a]indole[3′,2′:5,6]quinacridone (IDQA), which was synthesized by an improved procedure, have been carefully investigated and compared with its parent compound N,N′-di(n-octyl)quinacridone (C8-QA). Concentration-dependent 1H NMR spectra revealed that the strong aggregations of IDQA existed in solution because of the flat and extended π-conjugation. Two polymorphs of IDQA with and without π⋯π interactions exhibited red and non emissions, respectively. One-dimensional micromaterials with different morphologies constructed by IDQA molecules were fabricated by a reprecipitation approach and they displayed different emission properties due to the different molecular packing. The nine-ring fused flat skeleton endowed this material with several elegant properties, including a high photoluminescent quantum yield in solution, and a high thermal and electrochemical stability. Therefore, the efficient doped organic light emitting device (OLED) with IDQA as the emitter was fabricated. Moreover, the large π-conjugation system endowed the IDQA thin film with ordered molecular packing and good hole transport properties (hole mobility μh = 0.047 cm2 V−1 s−1).

A series of π-conjugated dendrimers Cn-QA and Tn-QA (n = 1–3) composed of quinacridone core and carbazole dendrons have been designed and synthesized. These dumbbell-like dendrimers with carbazole dendrons from first to third generation were achieved by convergent synthetic strategy. Their 1H NMR spectra, electrochemical, photophysical properties, and film formation behaviors as well as aggregation structures in solid states have been fully investigated. The relationships between the structures and properties of dendrimers have been established. The electron-withdrawing substituent effects and the limited conjugations of the carbazole dendrons have been studied. Compared with the parent molecule N,N′-di(n-butyl)quinacridone (DBQA), the HOMO levels of the dendrimers increased and the LUMO levels decreased due to the carbazole dendrons substitution. The absorptions and emissions of dendrimers displayed red-shift feature compared with that of DBQA, while the higher generation dendrimer displayed slightly blue-shift tendency compared with the lower one. The aggregation structures of films and solid powder samples could be efficiently modulated by the carbazole dendrons and tert-butyl groups. In particular, dendrimers C2-QA and C3-QA exhibited piezochromic luminescence phenomenon, and the mechanism was preliminarily investigated.

Two novel quinacridone (QA) cyclophanes with intrinsic intramolecular dye-dye interactions have been designed and synthesized. X-ray crystal structures as well as detailed photophysical properties have been well demonstrated. These two dyes have a major advantage that efficient fluorescence quenching can be observed even in their dilute solutions. A comparison of photophysical properties between the dimeric QA cyclophane and its reference monomeric counterpart indicates that the dimerization is predominant for the fluorescence quenching of QA dyes in solution. This study provided some model QA derivatives with dimeric structures for understanding the fluorescence quenching of QA dyes in solutions.

A series of cholesterol-appended quinacridone (QA) derivatives 1a–1d have been synthesized, in which 1b and 1c could form stable organogels in a wide range of organic solvents upon ultrasound irradiation. Field emission scanning electronic microscope (FESEM) and transmission electron microscopy (TEM) of xerogels or precipitates indicated that 1b and 1c formed 1D fibrous nanostructure, while 1a assembled into 3D flower-like microstructures. The ultrasound-induced organogel process was characterized by kinetic UV-vis and photoluminescence spectroscopic methods suggesting the formation of π-π aggregates in the gel state. Experimental results demonstrated that the ultrasound could promote molecules to contact frequently in the solution and induce semistable initial aggregates, which propagate to form nano/micro superstructures. The aggregation model was optimized by semiempirical AM1 calculation suggesting the hierarchical self-assembly process. In addition, the formed xerogel film exhibited mechanochromic property, and the phase transition process was accompanied by the fluorescence changes between yellowish green and orange.

The structures and properties of an indole-ring-fused quinacridone derivative 5,8,15,18-tetraoctyl-5,8,15,18-tetrahydroindolo[3,2-a]indole[3′,2′:5,6]quinacridone (IDQA), which was synthesized by an improved procedure, have been carefully investigated and compared with its parent compound N,N′-di(n-octyl)quinacridone (C8-QA). Concentration-dependent 1H NMR spectra revealed that the strong aggregations of IDQA existed in solution because of the flat and extended π-conjugation. Two polymorphs of IDQA with and without π⋯π interactions exhibited red and non emissions, respectively. One-dimensional micromaterials with different morphologies constructed by IDQA molecules were fabricated by a reprecipitation approach and they displayed different emission properties due to the different molecular packing. The nine-ring fused flat skeleton endowed this material with several elegant properties, including a high photoluminescent quantum yield in solution, and a high thermal and electrochemical stability. Therefore, the efficient doped organic light emitting device (OLED) with IDQA as the emitter was fabricated. Moreover, the large π-conjugation system endowed the IDQA thin film with ordered molecular packing and good hole transport properties (hole mobility μh = 0.047 cm2 V−1 s−1).

Two phenanthro[9,10-d]imidazole (PI) derivatives, 9-N,N-diphenyl-amino-10-(4-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)phenyl)anthracene (DPAA-PPI) and 9-N,N-dipheny-amino-10-(4-(1-(4-tert-butylphenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)phenyl)anthracene (tBuDPAA-PPI), have been designed and synthesized. The two compounds exhibited high photoluminescence quantum yields (at around 0.80) in the solid state and bipolar carrier transport properties. The non-doped OLEDs using DPAA-PPI and tBuDPAA-PPI as emitting layers showed the maximum power efficiencies (PEs) of 13.9 lm W−1 and 11.4 lm W−1, corresponding to the maximum external quantum efficiencies (EQEs) of 5.2% and 4.1%, respectively. The DPAA-PPI-based OLED exhibited an extremely low turn-on voltage of 2.4 V and its luminescence reached 100, 1000, 10000 and over 100000 cd m−2 under driving voltages of 2.8, 3.6, 5.1 and 7.5 V, respectively.

Acenaphtho[1,2-k]fluoranthene derivatives DPAF-n as new building blocks for one-dimensional (1D) structure assembly have been developed and employed to fabricate luminescent twisted nano/micro-wires; and the DPAF rigid core attached via flexible alkyl chains with suitable lengths is critical for the formation of twisted architectures.