Studies on Organoantimony and OrganoboronCompounds Containing Donor (D)–Acceptor(A) Motifs: Application to Anion Sensing and TADF for OLEDs

Abstract

This thesis describes research carried out on organoantimony and organoboron compounds containing donor-acceptor motifs, investigating their photophysical, electrochemical and/or electroluminescent properties. Chapter one gives a brief overview of fluoride sensing and organic light-emitting diodes. Chapter two describes the synthesis and photophysical studies of donor-antimony(V) lewis acids and its turn-on fluorescence response towards fluoride binding. The cationic antimony(V) compounds are almost nonemissive, but their fluorostiboranes display donor-centered fluorescence due to the locally excited * state. The carbazole donor containing compound exhibits the most intense turn-on fluorescence response toward fluoride binding with a high binding constant (K>107 M1) in MeCN. Chapter three presents synthesis and photophysical studies of a series of ortho-carbazole-appended triarylboron compounds (CzRoB, Cz = 9H-carbazolyl, R = electron-withdrawing groups; where the substituents (R) were introduced to the phenylene ring of the triarylboron acceptor moiety to control LUMO level. It was shown that gradual bathochromic shifts in emission wavelength could be attained by increasing the electron-withdrawing strength of R substituent due to the stabilization of the LUMO level. Chapter four discusses the perfluoro substitution effect on boron-based TADF compounds. A series of ortho-carbazole-appended triarylboron compounds were synthesized, in which the perfluoroalkyl (CF3 and C3F7) and perfluoroaryl (4-CF3C6F4) groups were introduced to induce the electron-inductive-effect and/or conjugated-effect. The compounds exhibit a light greenish to yellow emission in toluene with very high photoluminescence quantum yields up to 100% and show a small energy splitting (EST< 0.1 eV). The optimized OLEDs based on the CF3-substituted emitter (5) show a high external quantum efficiency of 29.9%with a low turn-on voltage of 2.35 V. In particular, the devices achieve an ultrahigh power efficiency (PE) of 123.9 lm/W without any light-outcoupling enhancement, which is among the best PE values for the reported TADF-OLEDs. Chapter five describes the noble ortho-donor-appended diboron compounds. A series of ortho-DAD emitters based on 9,10-dihydro-9,10-diboraanthracene (DBA) compounds in which different donor groups, such as carbazole (Cz), 3,6-Di-tert-butyl- carbazole (BuCz) or 9,9-dimethyl-acridine (DMAC), are appended to the ortho-position of the phenyl ring of the DBA acceptor, has been prepared. The low lying LUMO orbital of DBA core guaranty the red emissive TADF compound with DMAC. The photophysical studies of the ortho-DAD emitters suggest its potential application in TADF OLEDs.