Difluorinated cyclopentadithiophene derivatives for green emitters in organic light-emitting diodes: A theoretical investigation
Graphical abstract
Introduction
Small molecules based on 1,3,4-oxadiazole as an electron transport material are extensively studied because of their interesting properties. They may provide several benefits, such as good electron-withdrawing behavior, thermal and chemical stability, and tunable optical properties [[1], [2], [3], [4]]. Additionally, they have emerged as compounds with great utility in the field of medicinal and materials chemistry [5]. 1,3,4-Oxadiazole-based small molecules and polymers are used in organic applications as materials for organic light-emitting diodes (OLEDs) [6] and organic solar cells [[7], [8], [9]]. Besides, they are used as electron transport and hole-blocking materials in OLEDs [10,11]. Studies have revealed that the electron-deficient 1,3,4-oxadiazole may be incorporated with electron-rich conjugated segments acting as a donor to yield strong intramolecular charge transfer (ICT) [[12], [13], [14]]. Currently, donor-acceptor-type conjugated materials are of great interest because of their high molecular hyperpolarizability (β) and large dipole moment (μ), which can produce a third-order nonlinear optical (NLO) effect [15].
More recently, our research group has made a systematic effort to investigate theoretically two kinds of homodimer and co-dimer from cyclopentadithiophene (CPDT) derivatives [[16], [17], [18]], having rigid and planar structures added to their excellent electro-optical properties. Moreover, easier π→π* ICT is observed in various CPDT derivatives [19,20]. The bridge-head position was functionalized with electron-withdrawing groups, such as carbonyl (>CO) or dicyanomethylene (>CC–(CN)2). These groups can yield various donor-acceptor materials with a low band gap [21]. The factors influencing CPDT's semiconductor nature and charge carrier mobility were analyzed in detail, revealing the role of the bridging groups in CPDT-based materials. Meanwhile, carbonyl as a bridging group on CPDT induces ICT, resulting in photoluminescence quenching [16].
In view of these facts, we have designed new donor-acceptor conjugated molecules containing CPDT and 1,3,4-oxadiazole derivatives as donor and acceptor moieties, respectively (see Fig. 1).
The fluorine-substituted side chain of both donor-acceptor subunits will result in a significant increase in the rigidity of the backbone, as shown for fluoro anisole [22]. It is expected that the resulting molecules will exhibit better NLO properties.
In the present work, quantum theoretical calculations of the molecular structure of the two types of compounds were performed with density functional theory (DFT). The geometries of the compounds were optimized with the B3LYP hybrid functional (Becke's three-parameter hybrid exchange functional combined with the Lee-Yang-Parr correlation functional) in combination with the 6–311g(d,p) and 6–311++g(d,p) basis sets in tetrahydrofuran (THF). The estimated energy barriers of electron and hole injection into the compounds are based on calculations of the ionization potential (IP) and the electron affinity (EA) as well as the reorganization energies ( for hole and electron transport processes.
The most important properties that have to be controlled for OLEDs are the IP, EA, efficiency of charge carrier injection, electron and hole mobility, and light absorption and emission. To give a more quantitative description that can be related to the structure of organic electronic materials, it is important to understand the significant influence of tuning the molecular structure on electronic properties and device performance.
The time-dependent DFT (TD-DFT) method was used to calculate the absorption and emission spectra. The radiative lifetimes of spontaneous fluorescence from the lowest singlet excited state (S1) of the studied compounds were computed with use of the calculated emission energies and the oscillator strengths. The simulated current-voltage (I–V) characteristics and the spectral response of OLEDs were constructed with Silvaco TCAD software.
Section snippets
Computational methods
To understand the operation of OLEDs and predict theoretically their electric behavior, the electronic descriptors were introduced, computed, and compared. These descriptors include the energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) and the energy gap between the molecular orbitals of the two examples of CPDT derivatives. All calculations were performed with Gaussian 09 [23] by DFT at the B3LYP level of theory. Two basis sets,
Geometry and electronic structures
Firstly, the geometries of both molecules were optimized with the DFT/B3LYP and CIS methods in the S0 and S1 states, respectively, with use of the 6–311g(d,p) basis set. The results showed slight deviations from planarity for the two molecules. The dihedral angles 1 between CPDT and fumaronitrile and 2 between fumaronitrile and 1,3,4-oxadiazole units for the two compounds (see Fig. 2) in the S0 and S1 states are given in Table 1. The ground-state optimized structures proved that the two
Conclusion
The present work aimed to design theoretically two novel green fluorescent emitters with push-pull structures and high charge mobility to be effectively applied in OLEDs. Computational calculations using the DFT/B3LYP method with the 6–311g(d,p) and 6-311++g(d,p) basis sets were used in this investigation in THF solution with use of the conductor-like polarizable continuum model. The geometries of the ground state (S0) and the first excited state (S1) were optimized, and vertical excitation
Author contributions
Said HAJAJI: Conceptualization, Investigation, Methodology, Software, Validation, Visualization, and Writing - original draft.
Rania ZAIER: Methodology, Software, Validation and Visualization.
Sahbi AYACHI: Investigation, Methodology, Project administration, Supervision, Validation, Writing - review & editing.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
All calculations in this work were performed at the Center for Research on Microelectronics and Nanotechnology of Sousse, Tunisia.The authors are grateful to Sonia Ouada, English language teacher, National School of Engineers, for grammatical and language corrections.
References (40)
- et al.
Five-membered rings-triazoles, oxadiazoles, thiadiazoles
- et al.
Organic light-emitting diodes with 2-(4-biphenylyl)-5(4-tert-butyl-phenyl)-1,3,4-oxadiazole layer inserted between hole-injecting and hole-transporting layers
Vacuum
(2010) - et al.
Enhancement of efficiency in luminescent polymer by incorporation of conjugated 1,3,4-oxadiazole side chains as hole-blocker/electron-transporter
Synth. Met.
(2004) - et al.
Synthesis, characterization and photophysical properties of a new class of pyrene substituted 1,3,4-oxadiazole derivatives
Opt. Mater.
(2019) - et al.
The effect of molecular structure on intra-molecular charge-transfer in 1,3,4-oxadiazole derivatives
J. Photochem. Photobiol. Chem.
(2019) - et al.
Enhancement of intramolecular charge transfer strength in diphenylamine substituted symmetric 1,3,4-oxadiazole derivatives
RSC Adv.
(2019) - et al.
DFT and TD-DFT studies on the electronic and optical properties of linear π-conjugated cyclopentadithiophene (CPDT) dimer for efficient blue OLED
Opt. Mater.
(2019) - et al.
Optoelectronic properties of cyclopentadithiophene-based D-A copolymers as donors in BHJ organic solar cells: a theoretical study
J. Phys. Chem. Solid.
(2020) - et al.
About some properties of electro-synthesized short oligo(para-fluoro-anisole) (OPFA): a combined experimental and theoretical study
J. Mol. Struct.
(2011) - et al.
The DFT and MP2 based computational scrutiny on blue-shifted H–F stretching vibrational frequencies in hydrogen-fluoride complexes with nitriles: insights into the decisive role of intermolecular hydrogen bonding (IMHB) in ground and electronic excited states
Arab. J. Chem.
(2019)
Theoretical studies on electronic structures and photophysical properties of anthracene derivatives as hole-transporting materials for OLEDs
Spectrochim. Acta Part A Mol. Biomol. Spectrosc.
Theoretical study of α-fluorenyl oligothiophenes as color tunable emissive materials for highly efficient electroluminescent device
Org. Electron.
Molecular structures, spectroscopic (FT-IR, NMR, UV) studies, NBO analysis and NLO properties for tautomeric forms of 1, 3-dimethyl-5-(phenylazo)-6-aminouracil by density functional method, Spectrochim
Acta Part A Mol. Biomol. Spectrosc.
Study of the spectroscopic properties and first hyperpolarizabilities of disperse azo dyes derived from 2- amino-5-nitrothiazole
J. Photochem. Photobiol. Chem.
Structural parameters, electronic, linear and nonlinear optical exploration of thiopyrimidine derivatives: a comparison between DFT/TDDFT and experimental study
J. Mol. Struct.
Second and third-order nonlinear optical and DFT calculations on 2-amino-5-chloro pyridinium-L-tartrate: a phasematchable organic single crystal
Opt. Mater.
Prediction of structural, vibrational and nonlinear optical properties of small organic conjugated molecules derived from pyridine
J. Mol. Struct.
Nonlinear optical properties of urea
Opt Commun.
Bipyridyloxadiazoles as efficient and durable electron-transporting and hole-blocking molecular materials
J. Mater. Chem.
A NEw 1,3,4-oxadiazole-based hole-transport material for efficient CH3NH3PbBr3perovskite solar cells
Chem. Sustain. Chem.
Cited by (13)
Quantum computational investigation into optoelectronic and topological properties of a synthesized nanocomposite containing Hydroxyapatite-alt-Polyethylene Glycol (HAP/PEG)
2024, Colloids and Surfaces A: Physicochemical and Engineering AspectsExploration of intramolecular charge transfer in para-substituted nitrobenzofurazan: Experimental and theoretical analyses
2023, Spectrochimica Acta - Part A: Molecular and Biomolecular SpectroscopyComputational studies on optoelectronic and nonlinear optical properties of para-substituted nitrobenzofurazan compound
2023, Materials Today CommunicationsComputational modeling for the design of new fluorescent organic compounds based on both diketopyrrolopyrrole and nitrobenzofurazan moieties
2022, Journal of Molecular LiquidsCitation Excerpt :Molecular geometry of the designed molecules (both the neutral and charged) in ground states (S0) were fully optimized by employing the density function theory (DFT) at B3LYP (Becke three-parameter Lee-Yang-Parr) exchange–correlation functional [25,26] in conjunction with the 6–311 g(d,p) basis set. Calculations have been investigated in polar acetonitrile (CH3CN) by applying the conductor polarizable continuum model (CPCM) [27] with the Gaussian 09 program [28] and the output files were generated for use with Gauss View (5.0.8) program [29]. It should be noted that no imaginary frequency has been found in all cases, indicating that each compound optimized structure is at a local minimum.