Opposite behavior with an emission enhancement upon aggregation of the fluorophores is also known, but early reports are rare. [7] This phenomenon is coined aggregationinduced-emission (AIE) and became more popular through the work of Tang and co-workers since the early 2000s. [7,8,9] A plethora of molecules with AIE-behavior was investigated and a general understanding of their photophysical properties was achieved. [10,11] The emission quenching is referred to internal motion of suitable substituents like tetra phenylethylene and hexaphenylsilole at the fluorophore. [6,12] Rotation and vibration of these groups open non-radiative pathways which result in radiationless decay in solution. [9,13] Aggregation confines the flexibility of the substituents to restrict the internal motion. [14] Consequently, the non-radiative pathways are blocked, and the emission enhances in highly aggregated-solutions and in the solidstate. [11,15] Further strategies for obtaining solid-state luminescent materials aim at the introduction of bulky substituents at the fluorophores to prevent strong interchromophoric interactions. [16] These approaches are mainly based on intramolecular modifications and therefore the resulting fluorescence of the aggregates can be considered to be close to the emission from a monomeric state of the fluorophores.Controlling photophysical properties through non-covalent interactions (NCIs) [17] is more challenging. In early works, Jelley and Scheibe observed the appearance of new absorption and emission bands in pseudoisocyanine solutions with increasing dye-concentration, which were attributed to the formation of aggregates. [18] More recently a different approach for controlling and optimizing the photophysical properties of polyaromatic hydrocarbons in the solid-state has been successfully introduced. Instead of avoiding intermolecular interactions, molecules are designed, which allow specific interactions between their fluorophores in the aggregated state. The occurring π-π interactions lead to the formation of an excited dimer (excimer) after irradiation. [19] The formation of excimers in solution is well known since the investigations of the pyrene excimer by Förster [20] and Birks. [21] The typical features of spectral broadening and increased lifetime are also well investigated. In recent publications, this approach was successfully transferred to efficient solid-state emitters. Through control of the NCIs, the formation of excimers or exciplexes in the solid-state is possible and allows tuning of the photophysical properties. [22][23][24][25][26] Solid-state luminescent materials are essential for the development of optoelectronic devices like lasers, sensors, and organic light-emitting diodes. Organic molecules reveal several benefits like stability, costs, and environmental compatibility compared to metal-based materials. As common organic fluorophores often suffer from aggregation-caused quenching, different strategies have been established to overcome this quenching, which are mainly based...

On the basis of the bulky bis(4-benzhydryl-benzoxazyl-2-yl)methane ligand ( 4 -B z h H 2 Box 2 CH 2 ), neutral monovalent group 13 complexes [M 13 ( 4-BzhH2 Box 2 CH)] [M 13 = Tl (1), In (2), or Ga (3)] have been synthesized by salt metathesis reaction of the corresponding potassium or sodium precursor and TlOTf, InOTf, or "GaI". The diiodido gallium species [GaI 2 ( 4-BzhH2 Box 2 CH)] (3a) was realized as a byproduct once the synthesis of 3 was carried out at higher temperatures. The synthesis of [AlI 2 ( 4-BzhH2 Box 2 CH)] ( 6) as a potential precursor for an aluminum(I) congener was accomplished by two alternative synthetic routes. During one of those procedures, [AlMe 2 ( 4-BzhH2 Box 2 CH)] (4) was synthesized in good yields by deprotonation with an AlMe 3 solution (method A). Subsequently, 4 was converted to the monoiodinated species [AlMeI( 4-BzhH2 Box 2 CH 2 )] ( 5) using 1 equiv of I 2 or to 6 by iodination with 2 equiv of I 2 at 70 °C for 4 days. As an alternative, complex 6 could be prepared by iodination of 1 equiv of I 2 and [AlH 2 ( 4-BzhH2 Box 2 CH)] ( 7), which was previously obtained by facile reaction of 4-BzhH2 Box 2 CH 2 and AlH 3 NMe 2 Et. All main products 1−7 were completely characterized by nuclear magnetic resonance spectroscopy, mass spectrometry, elemental analysis, and single-crystal X-ray structure determination. Alane 7 was additionally analyzed by solid-state fluorescence spectroscopy. Density functional theory calculations on [M 13 ( 4-BzhH2 Box 2 CH)] [M 13 = Tl (1), In (2), Ga (3), or Al] revealed that the complexes consist of monovalent group 13 cations coordinated by an anionic ( 4-BzhH2 Box 2 CH) ligand similar to metallacycles incorporating a NacNac ligand.

Within this work, an aluminum dihydride complex ([(4‑MeBox2CH)­AlH2]) (1) based on the bis­(4-methyl-benzoxazol-2-yl)­methanide ligand was synthesized and characterized by spectroscopic methods (NMR, ATR-IR, and fluorescence), DSC (differential scanning calorimetry), mass spectrometry (LIFDI), and single crystal X-ray diffraction. The reactivity of alane 1 was investigated toward the reducing agents [DippNacNacAlI] and [(MesNacNacMgI)2], which gave the dialane compounds [(4‑MeBox2CH)­HAlII–AlIIH­(DippNacNac)] (2) and [{(4‑MeBox2CH)­AlIIH}2] (4a), respectively. Furthermore, dialuminoxanes [{(4‑MeBox2CH)­AlH}2(μ-O)] (4b) and [({(MesNacNac)­Mg}2(μ-H))­{H3AlII–AlIIH­(4‑MeBox2CH)}] (4c) were isolated as byproducts, with 4b co-crystallizing with 4a. The hydricity of both hydrides in the mixed-ligated dialane 2 were examined by a reaction with 1 equiv of trityl borate ([Ph3C]­[B­(C6F5)4]), which resulted in [(4‑MeBox2CH)­HAlII–AlII(DippNacNac)]­[B­(C6F5)4] (3). Due to the formation of 4b, complex 1 was reacted with 0.5 equiv of water, which causes the likely synthesis of insoluble oligomeric alumoxanes. To prevent this reaction and support the formation of well-defined dialumoxanes, 1 was initially converted to [(4‑MeBox2CH)­(DippO)­AlH] (5) by the deprotonation of 2,6-diisopropylphenol (propofol). This sterically encumbered compound 5 was subsequently reacted with 0.5 equiv of water, which resulted in defined molecules of [{(4‑MeBox2CH)­(DippO)­Al}2(μ-O)] (6). All these compounds exemplify the versatility of the 4‑MeBox2CH ligand in low-valent aluminum chemistry.

A novel sterically demanding bis(4‐benzhydryl‐benzoxazol‐2‐yl)methane ligand 6 (4−BzhH2BoxCH2) was gained in a straightforward six‐step synthesis. Starting from this ligand monomeric [M(4‐BzhH2BoxCH)] (M=Na (7), K (81)) and dimeric [{M(4‐BzhH2BoxCH)}2] (M=K (82), Rb (9), Cs (10)) alkali metal complexes were synthesised by deprotonation. Abstraction of the potassium ion of 8 by reaction with 18‐crown‐6 resulted in the solvent separated ion pair [{(THF)2K@(18‐crown‐6)}{bis(4‐benzhydryl‐benzoxazol‐2‐yl)methanide}] (11), including the energetically favoured monoanionic (E,E)‐(4‐BzhH2BoxCH) ligand. Further reaction of 4−BzhH2BoxCH2 with three equivalents KH and two equivalents 18‐crown‐6 yielded polymeric [{(THF)2K@(18‐crown‐6)}{K@(18‐crown‐6)K(4‐BzhBoxCH)}]n (n→∞) (12) containing a trianionic ligand. The neutral ligand and herein reported alkali complexes were characterised by single X‐ray analyses identifying the latter as a promising precursor for low‐valent main group complexes.

Three positional isomers of thiophosphoranyl anthracene were synthesized and their divers photophysical properties were investigated.