Synthesis and Photophysical Properties of a Series of Dimeric Indium Quinolinates

Yongseog Chung,Ju Hyun Hong,Sang Hoon Lee,Min Kim,Sang Woo Kwak,Myung Hwan Park,Youngjo Kim,Kang Mun Lee

doi:10.3390/molecules26010034

Abstract

A novel class of quinolinol-based dimeric indium complexes (1–6) was synthesized and characterized using 1H and 13C(1H) NMR spectroscopy and elemental analysis. Compounds 1–6 exhibited typical low-energy absorption bands assignable to quinolinol-centered π–π* charge transfer (CT) transition. The emission spectra of 1–6 exhibited slight bathochromic shifts with increasing solvent polarity (p-xylene < tetrahydrofuran (THF) < dichloromethane (DCM)). The emission bands also showed a gradual redshift, with an increase in the electron-donating effect of substituents at the C5 position of the quinoline groups. The absolute emission quantum yields (ΦPL) of compounds 1 (11.2% in THF and 17.2% in film) and 4 (17.8% in THF and 36.2% in film) with methyl substituents at the C5 position of the quinoline moieties were higher than those of the indium complexes with other substituents.

Highlights

The creation of tris(8-hydroxyquinolinato)aluminum (Alq3 ) by Tang and Van Slyke pioneered a new era of group 13-based organometallic luminescent materials that can be used in versatile optoelectronic fields [1]
These complexes are endowed with photophysical properties that originate from the control of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels
Scheme 1 shows the 1routes forthe theroutes synthesis dimeric quinoline-based indium comcomplexes which were produced in moderate yields

Summary

Introduction

The creation of tris(8-hydroxyquinolinato)aluminum (Alq3 ) by Tang and Van Slyke pioneered a new era of group 13-based organometallic luminescent materials that can be used in versatile optoelectronic fields [1]. Numerous efforts and approaches have been used to modulate the quinolinate ligands and expand their applications in organic light-emitting diodes (OLEDs) [2,3,4,5,6]. In this context, particular emphasis has been placed on the development of tris-incorporated metal complexes (Mq3 ). Owing to the ease of introducing various substituents at the C2 and C5 positions of the quinolinolate moiety, studies of various tris-organometallic complexes based on quinolinate derivatives have been conducted [7,8] These complexes are endowed with photophysical properties that originate from the control of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels. The systematic variation in the substituents at the C5 position of the quinolinolate groups led to excellent optical properties such as emission-color tuning and enhanced quantum efficiencies [9,10,11,12,13,14,15,16,17,18]

Methods

Results

Conclusion