Rational Design of π-Conjugated Tricoordinated Organoboron Derivatives With Thermally Activated Delayed Fluorescent Properties for Application in Organic Light-Emitting Diodes.

Ruifa Jin,Jingfan Xin

doi:10.3389/fchem.2020.577834

Abstract

A series of donor–acceptor (D–A) tricoordinated organoboron derivatives (1–10) have been systematically investigated for thermally activated delayed fluorescent (TADF)-based organic light-emitting diode (OLED) materials. The calculated results show that the designed molecules exhibit small singlet-triplet energy gap (ΔEST) values. Density functional theory (DFT) analysis indicated that the designed molecules display an efficient separation between donor and acceptor fragments because of a small overlap between donor and acceptor fragments on HOMOs and LUMOs. Furthermore, the delayed fluorescence emission color can be tuned effectively by introduction of different polycyclic aromatic fragments in parent molecule 1. The calculated results show that molecules 2, 3, and 4 possess more significant Stokes shifts and red emission with small ΔEST values. Nevertheless, other molecules exhibit green (1, 7, and 8), light green (6 and 10), and blue (5 and 9) emissions. Meanwhile, they are potential ambipolar charge transport materials except that 4 and 10 can serve as electron and hole transport materials only, respectively. Therefore, we proposed a rational way for the design of efficient TADF materials as well as charge transport materials for OLEDs simultaneously.

Highlights

Organic light-emitting diodes (OLEDs) have drawn considerable attention for applications in displaying and lighting fields owing to their outstanding advantages nowadays (Choy et al, 2014; Zhang et al, 2015; Im et al, 2017a; Liu et al, 2017b, 2018; Pal et al, 2018; Zhu et al, 2018)
Density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches have been remarkably successful in accurately evaluating a variety of ground and excited-state properties, in particular for thermally activated delayed fluorescence (TADF) materials (Lu et al, 2015a,b; Wang et al, 2017; Hussain et al, 2019)
Comparing the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) in S1 states with those in S0 states, we find that the electron density plots of both HOMOs and LUMOs in S1 states are similar to those in S0 states for all the investigated molecules, respectively

Summary

INTRODUCTION

Organic light-emitting diodes (OLEDs) have drawn considerable attention for applications in displaying and lighting fields owing to their outstanding advantages nowadays (Choy et al, 2014; Zhang et al, 2015; Im et al, 2017a; Liu et al, 2017b, 2018; Pal et al, 2018; Zhu et al, 2018). It is critically important to develop novel metal-free materials, which can be functionalized as efficient emitters and exhibit environment friendliness To address this issue, thermally activated delayed fluorescence (TADF) materials have been considered recently as promising candidates because of their potential in achieving 100% IQEs by harvesting all the triplet excitons (Uoyama et al, 2012; Wu et al, 2017; Yang et al, 2017; Chatterjee and Wong, 2019; Wang et al, 2019). Density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches have been remarkably successful in accurately evaluating a variety of ground and excited-state properties, in particular for TADF materials (Lu et al, 2015a,b; Wang et al, 2017; Hussain et al, 2019) In this regard, the rational design of a twisted donor– acceptor (D–A)-type structure can endow the molecules with TADF characteristics. The AIP, AEA, and λ for the electron (λe) and hole (λh) of the designed molecules were predicted at the B3LYP/631G(d,p) level

RESULTS AND DISCUSSION

CONCLUSION

DATA AVAILABILITY STATEMENT