Elsevier

Synthetic Metals

Volume 246, December 2018, Pages 39-44
Synthetic Metals

Photophysical, spectroscopic properties and electronic structure of BND: Experiment and theory

https://doi.org/10.1016/j.synthmet.2018.09.013Get rights and content

Highlights

  • Effects of solvent were studied on optoelectronic properties.

  • The optical and electrical conductance can be controlled with solvent environment.

  • BND compound in DCM is more stable than that of chloroform solvent.

  • B3LYP functional actually underestimates excited-state energies.

  • The theoretical calculations were found consistent with the experimental ones.

Abstract

The electronic structure, photophysical and spectroscopic properties of 2,5-Bis(1-naphthyl)-1,3,4-oxadiazole (BND) have been researched based on different solvent environments. The refractive index n is calculated using the semi-empirical relations based on measured energy gap Eg data. The lowest harmonic frequencies, Mulliken atomic charges, dipole moments, HOMO and LUMO energies were investigated using density functional theory (DFT). Moreover, ultraviolet-visible (UV–vis), energy gaps and radial distribution functions (RDFs) have been carried out using experiment and theory with B3LYP and CAM-B3LYP functionals. We also obtained the absorbance band edge and mass extinction coefficient of the BND solutions for dichloromethane (DCM) and chloroform. In addition, we investigated the optical and electrical conductance of the BND for related solvents. The HOMO and LUMO energy levels of the BND molecule in different solvent environments range from -2.17 to 2.21 eV and from -6.10 to -6.22 eV, indicating that the BND molecule will function well as electron transport materials in OLED applications. From obtained results, BND material has suitable optoelectronic parameters for the construction of functional materials, especially OLEDs.

Graphical abstract

Experimental and theoretical (for B3LYP and CAM-B3LYP functionals) results of density of state (DOS) spectrum and absorptivity spectra of BND organic molecule.

  1. Download : Download high-res image (227KB)
  2. Download : Download full-size image

Introduction

Organic light-emitting diodes (OLEDs) have a wide range of applications such as optical, electronic, optoelectronic and photonic technology [[1], [2], [3], [4], [5], [6], [7]]. Especially, OLEDs have widely been used in the panel displays and solid-state lightings [8,9]. To obtain the practical application of OLEDs, achieving highly efficient OLEDs with a simple structure is always essential [[10], [11], [12], [13]]. In this regard, the designed materials for OLEDs require special properties such as proper HOMO and LUMO energy levels [14], high luminescence efficiency [15], balanced charge-carrier mobility [16], and good stability [17]. Among OLEDs, oxadiazoles are the most widely used in areas in pharmaceutical chemistry and material science due to their remarkable optoelectronic properties [18]. In the literature, a series of available oxadiazoles and its derivatives were studied due to their high potential of electron-transporting from evaluating electron mobility, facile injection, good chemical and thermal stability [[19], [20], [21], [22], [23]]. Especially, compounds bearing the 1,3,4-oxadiazole core, mainly the 2,5-disubstituted ones, have been continuously developed due to their desirable optical and electronic properties that make them suitable candidates for the preparation of OLEDs [[24], [25], [26]]. Among these compounds, 2.5-bis(1-naphthyl)-1,3,4-oxadiazole (BND) is a very important material which exhibits the highest value of electron mobility than that of the other derivatives [27]. In this regard, various studies have been conducted on BND organic molecule. For example, the anthracene derivatives of BND have considerable potential as multifunctional layers and an electron transport layers in OLED [28].

Structure of organic compounds has a significant impact on the properties of materials, especially in the solvent environment [[29], [30], [31], [32]]. A solute-solvent morphology plays a crucial role in the performance of devices based on those materials because the solvent environments induce the significant changes in the physical and chemical properties of material [33]. To our knowledge, there is no any information on the photophysical, electronic structure and spectroscopic properties of BND organic material in different solvent environments. From this viewpoint, the major aim of the present study is to probe the features mentioned above of the BND organic material in different solvent environments using experimental technique and density functional theory (DFT) approach in the literature.

This article is organized as follows: we theoretically analyzed the lowest harmonic frequencies with positive value to gain insight into the most stable optimized structure. Then, Mulliken atomic charges, dipole moments, the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) and the frontier molecular orbital energy gap (HOMO–LUMO difference in energy gap,Eg) were investigated using DFT approach. These properties were controlled with different solvents such as dichloromethane (DCM), dichloroethane (DCE), dimethyl sulfoxide (DMS), acetonitrile and chloroform. Calculated Eg values obtained from B3LYP and CAM-B3LYP functionals were compared with the measured Eg values for different solvents. The calculated ultraviolet-visible (UV–vis) spectra obtained from time-dependent (TD)-DFT method have been compared with the measured results. In addition, the photoluminescence (PL) spectra have been calculated in different solvents based on TD-DFT calculations. The optical refractive index n is calculated using the semi-empirical relations based on measured energy gap Eg data. Later, the effects of the solvents on the mass extinction coefficient, αhϑ2 curves based on the photon energyE, density of state (DOS) spectrum obtained Mulliken population analysis, optical conductance σopt and electrical conductance σelect and the radial distribution functions (RDFs) were investigated. Finally, we discussed these parameters based on different solvent environments in detail.

Section snippets

Experimental details

DCM and chloroform solvents, and 2,5-bis(1-naphthyl)-1,3,4-oxadiazole (BND), whose synonym is 2,5-di(naphthalen-1-yl)-1,3,4-oxadiazole were purchased from a chemical company (Sigma-Aldrich, USA). The BND material was adjusted for 0.35 mM molarity and was separately dissolved in 20 mL volume of the DCM and chloroform solvents. Thence, we obtained the BND solutions for different solvents. Then, we took the measurements of the UV-spectra with a UV-1800 Spectrophotometer (Shimadzu model, Japan) at

Computational details

Photophysical, electronic structure and spectroscopic properties of BND organic material have been searched using DFT [34] with B3LYP functional [[35], [36], [37]] and 6–311 G (d, p) basis set. CAM-B3LYP [38] functional were also tested for accuracy and efficiency of the calculations because B3LYP actually underestimates excited-state energies [[39], [40], [41]]. Even so, the results obtained from B3LYP were also compared with CAM-B3LYP in this study because, especially for some molecular

Structural analysis

Optimized geometry of BND organic molecule with atom numbering calculated by B3LYP/6-311-G (d, p) is indicated in Fig. 1. From DFT calculations, the positive vibrational spectra were found that the optimized geometry is located at stationary point on the potential energy surface. The lowest vibrational harmonic frequencies of BND molecule are found to be 12.6, 12.7, 14.6, 14.4 and 13.9 cm-1 in DCM, DCE, DMS, acetonitrile and chloroform solvents, respectively. From this results, one can conclude

Conclusions

Based on the experimental and theoretical techniques, photophysical, electronic structure and spectroscopic properties of BND organic material have been investigated. From the results, the optimized structure with minimum total energy is the C1 form. Predicted band energy values using B3LYP functional give better results than that of CAM-B3LYP, comparing with experimental data, however; calculated molar extinction coefficients using CAM-B3LYP functional gives reasonable results than that of

Acknowledgments

The numerical calculations reported in this paper were partially performed at TUBITAK ULAKBIM, High Performance and Grid Computing Centre (TRUBA resources), Turkey. This work was supported by the Ahi Evran University Scientific Research Projects Coordination Unit. Project Number: PYO-FEN.4001.14.009.

References (50)

  • J. Chen et al.

    Mater. Today

    (2014)
  • A. Ltaief et al.

    Synth. Met.

    (2004)
  • M. Kurban et al.

    J. Mol. Struct.

    (2017)
  • C.-H. Chang et al.

    Dyes Pigm.

    (2015)
  • M. Reig et al.

    Dyes Pigm.

    (2017)
  • K. Krukiewicz et al.

    Synth. Met.

    (2016)
  • B. Gündüz et al.

    Vib. Spectrosc.

    (2018)
  • T. Yanai et al.

    Chem. Phys. Lett.

    (2004)
  • İ. Muz et al.

    Inorganica Chim. Acta

    (2018)
  • M. Kurban et al.

    Optik

    (2018)
  • S.K. Tripathy

    Opt. Mater.

    (2015)
  • M. Kurban et al.

    Chem. Phys. Lett.

    (2018)
  • S. Reineke et al.

    Nature

    (2009)
  • F. So et al.

    MRS Bull.

    (2008)
  • T. Nakayama et al.

    SID

    (2008)
  • J. Lee et al.

    ETRIJ

    (2016)
  • F. Wudl, G. Srdanov, US Patent 5189136,...
  • F.-M. Hsu et al.

    Chem. Mater.

    (2009)
  • K.T. Kamtekar et al.

    Adv. Mater.

    (2010)
  • B. Zhang et al.

    Adv. Mater.

    (2012)
  • Z. Yu et al.

    Adv. Mater.

    (2011)
  • S. Reineke et al.

    Nature

    (2009)
  • Y. Sun et al.

    Nature

    (2006)
  • J. Zhao et al.

    J. Mater. Chem. C

    (2018)
  • T.-H. Han et al.

    Sci. Adv.

    (2016)
  • Cited by (4)

    • Characterization, optical and nonlinear optical properties of TAZ organic material

      2019, Optik
      Citation Excerpt :

      The high efficiency of OLEDs with a simple structure has always been of great importance, for example by optics, electronics and optoelectronics, because of the wide range of applications [1–9].

    View full text