Computational study on thermally activated delayed fluorescence of donor–linker–acceptor network molecules

Abstract

We have investigated the structure property relationship of organic molecules with Donor-Linker-Acceptor (DLA) framework which can be used as precursors of OLED materials employing Density Functional Theory (DFT) and Time dependent DFT calculations. Two types of linkers' thiophene (π-conjugated) and ethylene (non-π-conjugated), carbazole as electron donor and cyano-substituted benzene as electron acceptor in DLA framework are chosen. Donor-Linker-Acceptor network allows the HOMO and LUMO orbitals to be spatially separated reducing the overlap of frontier orbitals decreasing the exchange energy (J) which results in smaller ΔEST (energy gap between excited singlet and triplet states) thus allowing us to realize metal free molecules suitable for OLED applications. Incorporation of donor and acceptor groups in the same moiety helps in reducing the number of layers conventionally used in OLEDS, reducing the cost with more simplified device fabrication. By enhancing the electron donating nature of donor group and increasing the withdrawing nature of acceptor group we observe a decrease in exchange energy, which is further decreased by a non-conjugated linker. Important properties like change in dipole moments, absorption and emission energies corresponding oscillator strengths, transport energy gaps, electron affinities, ionization potentials (vertical and adiabatic), reorganization energies, and exciton binding energies of various substituted molecules are investigated and their role in determining the efficiencies are discussed. In order to account the effects of solvents and their role in altering various properties, the studies are carried out in polar and non-polar solvent phases in addition to the gas phase calculations. Please do not adjust marginsPlease do not adjust margins towards HOMO are found to be 89%, 9% and 2% and for LUMO 2%, 35% and 63% respectively. For 2.a, the contribution of donor, linker and acceptor towards HOMO are found to be 95%, 4% and 1% and for LUMO 1%, 4% and 95% respectively. Figure 3. HOMO, LUMO orbitals of molecules with thiophene linker (1.a-1.e) and ethylene linker (2.a-2.e). Grey, white, blue, red and yellow colours indicate carbon, hydrogen, nitrogen, oxygen and sulphur atoms respectively. Graphical AbstractWe have investigated the structure property relationship of organic molecules with Donor-Linker-Acceptor (DLA) framework which can be used as precursors of OLED materials employing Density Functional Theory (DFT). Two types of linkers thiophene (π-conjugated) and ethylene (non-πconjugated), carbazole as electron donor and cyano-substituted benzene as electron acceptor in DLA framework are chosen. By enhancing the electron donating nature of donor group and increasing the withdrawing nature of acceptor group we observe a decrease in exchange energy, which is further decreased by a non-conjugated linker. Important properties like energy gap between excited singlet and triplet states, change in dipole moments, absorption and emission energies corresponding oscillator strengths, tra...

Limitations of Global Hybrids in Predicting the Geometries and Torsional Energy Barriers of Dimeric Systems and the Role of Hartree Fock and DFT Exchange

“…[1][2][3][4][5] For example, a twist in dihedral angle between donor and acceptor moieties is required to reduce the overlap between HOMO and LUMO wave functions to decrease the exchange integral (J) and lower the singlet-triplet energy gaps, which is a crucial parameter in determining the efficiency of OLED molecules. [4] On the other hand, planarity between these groups is required to enhance the efficiency in photo voltaic applications of solar cells. [6] The impact of dihedral (torsional) angle in varying the bandgaps of polymers is predominantly high even compared to the strength of donor or acceptor groups substitution to the polymeric backbone.…”

“…Accurate prediction of geometry plays a decisive role in evaluating various properties like band gaps, exchange energies, singlet‐triplet energy gaps, spin orbit coupling interactions, optical gaps, exciton binding energies, and so forth . For example, a twist in dihedral angle between donor and acceptor moieties is required to reduce the overlap between HOMO and LUMO wave functions to decrease the exchange integral (J) and lower the singlet‐triplet energy gaps, which is a crucial parameter in determining the efficiency of OLED molecules . On the other hand, planarity between these groups is required to enhance the efficiency in photo voltaic applications of solar cells .…”

Impact of non‐empirically tuning the range‐separation parameter of long‐range corrected hybrid functionals on ionization potentials, electron affinities, and fundamental gaps

“…These materials are gradually replacing the traditional materials (e.g., their inorganic counterparts) in different fields that have been dominating the markets over the past few decades. The function and performance of these materials depends heavily on their optoelectronic properties, including the vertical ionization potentials (IPs), vertical electron affinities (EAs), fundamental gaps (FGs), optical gaps, and so forth . For example, organic light emitting diodes contain several layers of different stacked organic films, and there exists an energy barrier to the flow of charge between these layers, therefore, the knowledge of transport energy levels is required along with IPs, EAs, and FGs that can help in optimizing and designing the devices with higher efficiencies.…”

Assessing the role of Hartree-Fock exchange, correlation energy and long range corrections in evaluating ionization potential, and electron affinity in density functional theory

“…With the widespread usage and growing interest in organic semiconductors (OSCs) due to their versatile properties and their potential in replacing the inorganic counterparts in application of various technologies like photovoltaics (PVs), thin field transistors, light emitting diodes (LEDs) devices, etc., accurate determination of ionization potentials (IPs), electron affinities (EAs), and frontier molecular orbital energies of OSCs attracts a great attention. Precise prediction of IPs, EAs helps in determining various properties like exciton binding energies, electron, and hole injections, which plays a crucial role in determining the efficiencies of these devices and calculation of accurate transport energy levels (HOMO, LUMO) helps in the right choice of selection of electrodes in OLEDs and solar cells setup . Hence, a reliable theoretical methodology, which predicts the above mentioned properties accurately is required to design and develop the devices of higher efficiencies.…”