66 Table 3.4: Different device parameters of the PLEDs based on these newly synthesized carbazole-based copolymers. 130 Table 5.2: Photophysical properties and energy levels of the DT1 and DP1 monomers 130 Table 5.3: Device characteristics of WPLEDs.
Introduction to Organic Semiconductors
Due to lower energy of the bonding (π) orbital both the 2Pz electrons will occupy this orbital, leaving the anti-bonding (π*) orbital without electrons. In the later sections, the main discussion consists of the development of organic semiconductor materials for the production of efficient OLEDs/PLEDs.
Invention of Light Bulb
By chemically doping the CPs, the photophysical and electrochemical properties can be improved, and as shown in Figure 1.2, many derivatives of CPs are synthesized and investigated. 8 organic field-effect transistors (OFETs),9-12 organic photovoltaic devices (OPVs)13-15 and biosensors.16 There are certain challenges to be met in terms of high photoluminescence (PL) quantum yields, mainly in the solid state and environmental stability of the organic semiconductors.
Organic Light Emitting Diode (OLED)
Unlike conventional incandescent bulbs and compact fluorescent tubes (CFLs), SSL uses a semiconductor light-emitting diode (LED), where light is produced directly by the principle of electroluminescence (EL). Furthermore, since OLEDs are broadband emitters, they have the ability to exhibit a very good CRI, which is not the case for cheap inorganic LEDs.
History of Electroluminescence
In the last few decades, a new field of research called solid state lighting (SSL) has emerged. The biggest breakthrough in OLED came later in 1987 when Ching W.
Advantages and Disadvantages of OLEDs
Advantages
In addition, the same group also reported EL in a small molecule anthracene crystal with a thickness from 10 µm to 5 mm for a voltage of several hundreds of volts applied across it.25 Later in the year 1983, P. This flexibility due to the solution processing method creates a new challenge in the solubility of the polymers, which was solved by introducing the less polar alkyl chains on the backbone of the polymers.
Disadvantages
High brightness and high resolution: OLEDs are very bright at low operating voltage (white OLEDs can be bright up to 150,000 cd/m2). Wide viewing angle: OLED emission is lambartic, so the viewing angle is as high as 160 degrees.
Basic Structure of OLED and EL Mechanism
By applying the voltage to the device, the electrons and holes are injected into the LUMO and HOMO of the organic material from the cathode and anode, respectively (Figure 1.4). These inserted layers can facilitate efficient injection and enhance the exciton formation, due to the well-balanced charge that also shifts the recombination zone to the center of the active layer.
Characterization Parameters for Organic Light Emitting Diodes
The most important point is that the exciton zone must be in the center of the active layer (emissive layer), therefore it is necessary that organic materials have identical mobility of electrons and holes. The efficiency of the device depends mainly on the number of charges inserted in active materials and the number of electrons and holes that recombine.
Materials for the OLED
To be used for indoor lighting, a light source must have a minimum CRI value greater than or equal to 80. Some of the aromatic amines such as N,N'-di(naphthalen-1-yl)-N, N'-diphenyl-biphenyl-4,4'-diamine (NPD), bis-(4-carbazol-9-yl)-biphenyl (CBP) N,N'-Bis(3-methylphenyl)-N,N'- diphenylbenzidine (TPD) and tris-(4-carbazol-9-yl-phenyl)-amine (TCTA) (Figure 1.6) are typical hole-transporting materials for OLED applications.
Small Molecules as Active Materials
Polymers as Active Materials
The emission colors of the devices exhibited orange to red light (570–600 nm) and were slightly red-shifted gradually with increasing BSeD concentrations in the PF backbone. The emission colors of the device showed predominantly red emission, which was attributed to the red emitting monomers.62.
Aggregation Induced Emission Luminogens as Active Materials
Blue Emitting AIE Active Materials
EL of BTTPPE emits blue color at ∼448 nm and exhibits lower EL properties (2.8 cd A-1 and 1.6%).90 This is due to low conjugation caused by steric crowding between the triphenylvinyl units. The EL device was fabricated with ITO/NPB/BTPE/TPBi/Alq3/LiF/Al configuration and it exhibits the emission at ~488 nm with peak brightness of 11180 cd m-2, current efficiency of 7.26 cd A-1 and EQE of 3.17%.91 The devices showed low turn-on voltage (4 V), clearly indicating that BTPE is a promising active material for OLEDs (Figure 1.13).
Green Emitting AIE Active Materials
The PTPE compound exhibits the green EL at ~520 nm, which is very similar to the PL spectra. These compounds showed good results with the highest brightness of 14100 cd m-2, highest current efficiency of 8.8 cd A-1 and power efficiency of 7.8 lm W-1 for TPE-4TPA.
Red Emitting AIE Active Materials
Moreover, the voltage-independent EL spectra were easily achieved by incorporating the active AIEE monomers into the polymer host. This is due to the non-flatness of the active AIEE molecules that can effectively reduce TH.
An OLED device is a semiconductor device that requires high solid-state quantum yields with organic materials with a well-balanced charge. The introduction of donor-acceptor moieties into the AIE active core can show high solid-state quantum yields and achieve better device performance, which has great scope for future development.
Synthesis and Characterization of Color Tunable, Highly
Experimental section
- Materials and measurements
- Synthesis of 4-bromo-9-N-4-bromophenyl-1,8-naphthalimide (2)
- General polymerization procedure
- Poly[2,7-(9,9’-dioctylfluorene)-co-N-phenyl-1,8-naphthalimide]
- Poly[2,7-(9,9’-dioctylfluorene)-co-N-phenyl-1,8-naphthalimide]
- Poly[2,7-(9,9’-dioctylfluorene)-co-N-phenyl-1,8-naphthalimide]
- Poly[2,7-(9,9’-dioctylfluorene)-co-N-phenyl-1,8-naphthalimide]
- Poly[2,7-(9,9’-dioctylfluorene)-co-N-phenyl-1,8-naphthalimide]
- PLED fabrication and characterization
1H NMR and 13C NMR spectra were recorded on Varian AS 400 MHz and Bruker 600 MHz NMR spectrometers. Current density–voltage (J–V) characteristics of the fabricated PLEDs were measured using a Keithley 2400 source meter, whereas the luminance and EL spectra were recorded using an LCS-100 integrating sphere.
Results and discussion
- Synthesis and characterization of the polymers
- Optical and photoluminescence properties
- Electrochemical and Electroluminescence properties
The emission color of the PFO is completely quenched due to energy transfer from the PFO to NPN unit. The peak in the blue region is due to the fluorene unit, while the peak in the green region is due to the NPN unit. It was observed that the intensity of the green peak increases when the NPN content in the polymer chain is increased.
As the concentration of the NPN unit increases, the electron-accepting capacity of the polymer increases.
Summary
Color Tunable Donor-Acceptor Electroluminescent Copolymers
Experimental Section
- Materials and Measurements
- General polymerization procedure
- Poly[3,6-(9,-octylcarbazole)-co-N-phenyl-1,8-naphthalimide](PCzNPN50)
- Poly[3,6-(9,-octylcarbazole)-co-N-phenyl-1,8-naphthalimide]
- Poly[3,6-(9,-octylcarbazole)-co-N-phenyl-1,8-naphthalimide]
- Poly[3,6-(9,-octylcarbazole)-co-N-phenyl-1,8-naphthalimide]
- Poly[3,6-(9,-octylcarbazole)-co-N-phenyl-1,8-naphthalimide]
- Poly[3,6-(9,-octylcarbazole)-co-N-phenyl-1,8-naphthalimide]
- PLEDs Fabrication and characterization
The reaction mixture was degassed three times by freeze-thaw cycles to completely remove any traces of oxygen and purify the argon gas to create an inert atmosphere. The reaction mixture was stirred at 80°C for 48 hours and iodobenzene was added as a final cap. Finally, after 4 hours, the benzeneboronic acid was added to the reaction mixture as another end cap and the reaction was continued for another 4 hours.
The reaction mixture was then cooled to room temperature, poured into 100 mL methanol and further stirred at room temperature for 3 h.
Results and discussion
- Synthesis and characterization of the polymers
- Electrochemical properties
- Electroluminescence properties
The TGA curves and starting decomposition temperature (Td) for the copolymers are shown in Figure 3.3a and Table 3.1. The DSC curves and the glass transition temperature (Tg) of the copolymers are shown in Figure 3.3b and Table 3.1. The oxidation onset values, energy levels (HOMO and LUMO) and band gaps of the copolymers are summarized in Table 3.3.
The optical band gaps were estimated from the initial absorption spectra of the CPs in the thin film state.
Summary
Monosubstituted Dibenzofulvene-Based Luminogens: Aggregation-
Experimental section
- Materials and measurements
- Synthesis of 4-Bromo-7-(4-methoxy-phenyl)-benzo[1,2,5]thiadiazole (1)80
- Synthesis of 5-[7-(4-Methoxy-phenyl)-benzo[1,2,5]thiadiazol-4-yl]-
- Synthesis of 4-(5-Bromo-thiophen-2-yl)-7-(4-methoxy-phenyl)-
- Synthesis of 4-{5-[7-(4-Methoxy-phenyl)-benzo[1,2,5]thiadiazol-4-yl]-
- Synthesis of 4-{5-[4-(2,7-Dibromo-fluoren-9-ylidenemethyl)-phenyl]-
- Synthesis of 4-[5-(4-Fluoren-9-ylidenemethyl-phenyl)-thiophen-2-yl]-7-(4-
- Synthesis of 4-(5-Fluoren-9-ylidenemethyl-thiophen-2-yl)-7-(4-methoxy-
- Crystal Data
The residue was purified by column chromatography to give the product as an orange solid compound DP2. The residue was purified by column chromatography to give the product as a red solid compound DT2. The residue was purified by column chromatography to give the product as an orange solid compound DP1.
The residue was purified by column chromatography to give the product as an orange solid compound DT1.
Results and discussion
- Optical and photoluminescence properties
- Intramolecular Charge Transfer (ICT)
- Aggregation Induced Emission Enhancement (AIEE) Properties
- Density Functional Theory (DFT) Calculations
As shown in Figure 4.4 (summarized in Table 4.3), the UV-vis spectra of the luminogens were modified when the solvent polarity was changed from non-polar to polar. Furthermore, Figure 4.8a-d shows the PL spectra, relative intensity and actual changes in the solution color of DP1 and DP2 in water and THF mixtures (40 μM) with different fw. As shown in the structure of DT1 (Figure 4.9b-d), two adjacent molecules are packed with highly tilted and end-to-end arrangement as dimers through intermolecular S···S interactions (3.596 Å) between the thiophene 'S' from one molecule.
The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of luminogens were assessed by cyclic voltammetry (CV) (Figure 4.18).
Summary
To confirm the dual state property of DP1 and DP2, the AIEE studies were also conducted. These results showed that DP1 and DP2 luminogens possessed exceptional optical properties with dual emission behavior. Incorporation of the phenyl ring between the thiophene and DBF led to the twisted conformations in the aggregated state and stiffer conformations in solution due to the extensive conjugation.
Based on these results, we concluded that M-DBF acts as a mediator between ACQ and AIE materials, and this strategy provided a new class of AIE and dual-state active materials.
Saturated and Stable White Electroluminescence from Linear Single
- Experimental section
- Materials and measurements
- General polymerization procedure
- Poly[2,7-(9,9’-dioctylfluorene)] (PFO)
- Poly[2,7-(9,9’-dioctylfluorene)-co-4-[5-(4-Fluoren-9-ylidenemethyl-
- Poly[2,7-(9,9’-dioctylfluorene)-co-4-[5-(4-Fluoren-9-ylidenemethyl-
- Poly[2,7-(9,9’-dioctylfluorene)-co-4-[5-(4-Fluoren-9-ylidenemethyl-
- Poly[2,7-(9,9’-dioctylfluorene)-co-4-(5-Fluoren-9-ylidenemethyl-
- Poly[2,7-(9,9’-dioctylfluorene)-co-4-(5-Fluoren-9-ylidenemethyl-
- Poly[2,7-(9,9’-dioctylfluorene)-co-4-(5-Fluoren-9-ylidenemethyl-
- WPLEDs Fabrication and characterization
- Results and discussion
- Synthesis and characterization of the polymers
- Optical Properties
- Electrochemical Properties
- Summary
- References
This is due to too low concentrations of M-DBF in the main chain of the polymer. In contrast, the solid state of the copolymers shows a dominant blue emission from the PFO main chain along with an additional peak in the orange region. The monomer concentrations (DT1 or DP1) were carefully adjusted in the PFO backbone to create a partial energy transfer from the PFO to the monomers, thereby achieving the desired white light.
As shown in Figure 5.3b, the PL intensity of the copolymers depended on the monomer concentrations in the polymer backbone, and the PL intensity was directly proportional to the monomer concentration.
Bridge-Driven Aggregation control in Dibenzofulvene-Naphthalimide
Experimental section
- Materials and Instrumentation
- Synthesis of 4-(2-Cyclohexyl-1,3-dioxo-2,3-dihydro-1H-
- Synthesis of 5-(2-Cyclohexyl-1,3-dioxo-2,3-dihydro-1H-
- Synthesis of 2-Cyclohexyl-6-[4-(2,7-dibromo-fluoren-9-ylidenemethyl)-
- Synthesis of 2-Cyclohexyl-6-[5-(2,7-dibromo-fluoren-9-ylidenemethyl)-
- Synthesis of 2-Cyclohexyl-6-(4-fluoren-9-ylidenemethyl-phenyl)-
- Synthesis of 2-Cyclohexyl-6-(5-fluoren-9-ylidenemethyl-thiophen-2-yl)-
- Crystal Data
The residue was purified by column chromatography to give product as a yellow solid compound DP2NC. The residue was purified by column chromatography to give product as an orange solid compound DT2NC. The residue was purified by column chromatography to give product as a yellow solid compound DP1NC.
The residue was purified by column chromatography to give product as an orange solid compound DT1NC.
Results and discussion
- Synthesis and characterization
- Solvatochromism
- Aggregation Induced Emission Enhancement (AIEE) Properties
- Density Functional theory (DFT) Calculations
- Electrochemical properties
- Thermal Properties of the Luminogens
However, the arrangement of the DBF part is different compared to that of the NC part. As shown in Figure 6.7, the two DP2NC luminogens are strongly packed by C-H···π (2.841 Å) intermolecular interactions. This is due to the greater electron-donating capacity of the thiophene bridge-substituted DBF moiety.
The thermal properties of the four luminogens were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), and the curves are shown in Figure 6.15.
Summary
