Chemical modification of phenothiazine-benzophenone derivatives tunes the emission behavior from triplet states by selecting the geometry of the intramolecular charge transfer (ICT) state.Afundamental principle of planar ICT (PICT) and twisted ICT (TICT) is demonstrated to obtain selectively either room temperature phosphorescence (RTP) or thermally activated delayed fluorescence (TADF), respectively.T imeresolved spectroscopya nd time-dependent density functional theory (TD-DFT) investigations on polymorphic single crystals demonstrate the roles of PICT and TICT states in the underlying photophysics.This has resulted in aRTP molecule OPM,w here the triplet states contribute with 89 %o ft he luminescence,a nd an isomeric TADF molecule OMP,w here the triplet states contribute with 95 %ofthe luminescence.

Chemical modification of phenothiazine-benzophenone derivatives tunes the emission behavior from triplet states by selecting the geometry of the intramolecular charge transfer (ICT) state.Afundamental principle of planar ICT (PICT) and twisted ICT (TICT) is demonstrated to obtain selectively either room temperature phosphorescence (RTP) or thermally activated delayed fluorescence (TADF), respectively.T imeresolved spectroscopya nd time-dependent density functional theory (TD-DFT) investigations on polymorphic single crystals demonstrate the roles of PICT and TICT states in the underlying photophysics.This has resulted in aRTP molecule OPM,w here the triplet states contribute with 89 %o ft he luminescence,a nd an isomeric TADF molecule OMP,w here the triplet states contribute with 95 %ofthe luminescence.

(2017) 'Synthesis, diastereomer separation, and optoelectronic and structural properties of dinuclear cyclometalated iridium(III) complexes with bridging diarylhydrazide ligands. ', Organometallics., 36 (5). pp. 981-993.Further information on publisher's website:https://doi.org/10.1021/acs.organomet.6b00887Publisher's copyright statement:This document is the Accepted Manuscript version of a Published Work that appeared in nal form in Organometallics, copyright c 2017 American Chemical Society after peer review and technical editing by the publisher. To access the nal edited and published work see https://doi.org/10.1021/acs.organomet.6b00887. Additional information:Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. ABSTRACT: A series of diiridium complexes 13-16 bridged by diarylhydrazine ligands and cyclometalated by phenylpyridine or phenylpyrazole ligands was synthesized. In all cases the ɅΔ meso and ɅɅ/ΔΔ rac diastereomers were separated and characterized by single-crystal X-ray diffraction, revealing intramolecular - stacking between arenes of the bridging and cyclometalating ligands. Density functional theory (DFT) calculations show that in general the HOMOs are mainly localized on the iridium centers, the cyclometalating phenyl moieties and the central hydrazide components of the bridging ligands, while the LUMOs are primarily localized on the N-heterocycles (pyridine or pyrazole) of the cyclometalating ligands. This series of complexes, especially with the separated diastereomers, provides an ideal opportunity to study the effects of subtle structural changes on the optoelectronic properties of diiridium systems: significant differences are observed between the rac and meso isomers in some cases. A cyclic voltammetric study of the electrochemical properties of the eight complexes reveals strong intramolecular interactions between the iridium centers. The photophysical properties are reported in solution, and in rigid poly(methyl methacrylate) (PMMA) or 2-methyltetrahydrofuran (2-MeTHF) (at 77 K) matrices where some of the complexes are strongly emissive in the turquoise and green regions (Φ PL 42-68 ±10%) due to matrix-induced restricted intramolecular motion (RIM).

The potential of intramolecular π-π interactions to influence the photophysical properties of diiridium complexes is an unexplored topic, and provides the motivation for the present study. A series of diarylhydrazide-bridged diiridium complexes functionalised with phenylpyridine (ppy)-based cyclometalating ligands is reported. It is shown by NMR studies in solution and single crystal X-ray analysis that intramolecular π-π interactions between the bridging and cyclometalating ligands rigidify the complexes leading to high luminescence quantum efficiencies in solution and in doped films. Fluorine substituents on the phenyl rings of the bridge promote the intramolecular π-π interactions. Notably, these non-covalent interactions are harnessed in the rational design and synthesis of the first examples of highly emissive sky-blue diiridium complexes featuring conjugated bridging ligands, for which they play a vital role in the structural and photophysical properties. Experimental results are supported by computational studies.

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To conclude, it is worth noting that although the results presented here are mainly qualitative, the technique employed allows (1) the detection of the presence of different conformers of a molecule in the gas phase and the estimation of their energy differences and (2) the detection of molecular complexes and the study of their polarity, which gives insight into their structure and symmetry.