Modulation Of The Molecular Structures Of Cationic Iridium Complexes:Photoelectric Performance And Structure-property Relationship

Organic-metal based photoelectric materials have attracted increased attention in material science due to their easy synthesis, tunable emission wavelength and flexible displays during the past two decades. Phosphorescent Ir(III) complexes are capable of utilizing both singlet and triplet excitions by means of enhanced intersystem crossing(ISC), via the heavy atom effect, and have been used widely to increase the emission yield to 100% theoretically. In particular, cationic Ir(III) complexes become star molecule as a class of excellent organic photoelectric materials, because of their promise for applications in electroluminescence, cell imaging, chemical sensor as well as catalytic reaction owing to their unique advantages of tailor preparing method, easy purification as well as tunable emission colors. Nevertheless, there are currently two issues which have limited their applications in the fields of electroluminescence(EL). On the one hand, the severe concentration quenching effects in the emission layer will drastically decrease the device efficiencies; on the other hand, luminescent molecule are vulnerable to nucleophilic attack in the operation process of devices, which increases the possibility of ligand-exchange reaction, leading to low operational stability. Given these considerations, introducing steric hindrance into ligands of the complexes, and designing and synthesizing novel materials with aggregation-induced emission(AIE) characteristics are effective strategies to suppress the concentration quenching and enhance the device performance. Moreover, in terms of improve the operational stability and efficiency of functional devices, constructing supermolecular cage molecules are feasible approaches to avoid nucleophilic attack.In this paper, in order to overcome these problems which have limited cationic Ir(III) complexes applications in the fields of electroluminescence, we designed and synthesized a series of novel cationic Ir(III) complexes and investigate structure-photoelectric properties relationships via experimental methods and theoretical calculation.1. By modifying the phenylpyridine groups, supermolecularcage cationic Ir(III) complexes consisted of cyclometalated ligands with suspended benzene and rigid ancillary ligands were synthesized, their photophysical and electroluminescence properties were investigated in detail. The results suggested that the dual strong π-π interaction caused by suspended benzene of cyclometalated ligands have a negative effecton the operational stability of devices because of the high steric hindrance effection involved.2.Cationic Ir(III) complexes with AIE characteristics have been synthesized, their structure-property relationships and charge carrier injection/transporting were successful explored. The experimental results indicated that their photoelectric characters can be tuned dramatically by suitable chemical modifications, which can exhibit aggregation-induced emission(AIE) properties and effectively suppress the quenching of luminescence, thus simultaneously improve the device performance.3. Based on pyrazoline derivatives, a series of AIE-activecationic iridium(III) complexes were designed and synthesized, which simultaneously experience strong π-π stacking interactions in the face to face packing manner. Their photophysical and electroluminescence properties were systematically studied. In addition, the selective detection of TNP(2, 4, 6-trinitrophenol) using these complexes as chemosensors has been successfully realized. The experimental results clearly revealed that the strong π-π interactions existed in intermolecular have the benefit of improving the device stability, while the molecules bearing AIE character could overcome the concentration quenching effect, thus enhancing the EL performance. Owing to their two unique features, these novel cationic iridium(III) complexes are of great value for the practical application of functional devices.4. A series of orangecationic iridium(III) complexesbased on phenylisoquinolineand 1-phenyl-3, 4-dihydro-isoquinolinewere synthesized and their photophysicaland photocatalytic hydrogen production properties were well investigated. As a result, 1-phenyl-3, 4-dihydro-isoquinoline has a substantial impact on excited states lifetimes, although the nature of their excited states and emission color seldom changedcompared with their parent complexes. Hence, these complexes exhibited remarkably photocatalytic behavior due to long excited states lifetimes, broad and strong absorption as well as separated holes and electrons.