Ring Size Effects on Multi‐Stimuli Responsive Luminescent Properties of Cyclic Amine Substituted β‐Diketones and Difluoroboron Complexes

Abstract

Emissive b-diketones (bdks) and difluoroboron complexes (BF 2 bdks) show multi-stimuli responsivel uminescence in both solution and the solid state. As eries of bdk ligands and boron coordinated dyes were synthesized with different cyclic amine substituents in the 4-position to explore ring size effects on variousl uminescent properties, including solvatochromism, viscochromism, aggregation-induced emission (AIE), mechanochromic luminescence( ML) and halochromism. Red-shifted absorption and emission were observed in CH 2 Cl 2 forb oth bdk ligandsa nd boron dyes with increasing substituent ring size. The compounds displayed bathochromic emission in more polar solvents, and higher fluorescence intensity in more viscous media. The AIE compounds exhibited enhanced emission when aggregated. For solid-statep roperties, al arge emission wavelength shift was shown for the piperidine substituted bdk after melt quenching on weighing paper.L arge blue-shifted emissions were observed in all the boron dye spin cast films after trifluoroacetic acid vapor annealing, and the original emissions were partially recovered after triethylamine vapor treatment.

Recent advances in the synthesis of luminescent tetra-coordinated boron compounds

“…Boronβ-diketonates showed interesting properties such as aggregation induced emission (AIE), mechanochromic luminescence (ML), solvatochromism, and viscochromism. 23,24 Recently, boron-coordinated β-diketonates having a triphenylamine moiety (4) that exhibits different fluorescent colour in the amorphous and crystalline states were reported. The red emission of the amorphous state and orange emission of the crystalline state were able to be reversibly switched by grinding and fuming processes.…”

“…Compound 21 also exhibits reversible mechanochromic behaviour with the emission colour changing between yellow and orange-red upon grinding and fuming. 39 The mechanochromic behaviour of a series of aryl groups with carbonyl substituted-boron-β-diketonates was studied (23)(24)(25). Combined experimental and theoretical studies reveal the presence of a varying number of straps in the amorphous and crystalline states which are responsible for the mechanochromic behaviour.…”

Supercooled Liquid β-Diketones with Mechanoresponsive Emission

“…Because of their facile synthesis from commercially available starting materials and tunable optical properties, luminescent β-diketones (bdks) are a particularly promising class of stimuli-responsive materials. Their emission properties are tunable via boron coordination, alkyl chain length, , substituent ring size, heavy atom, , and donor and acceptor substitution, , as well as heteroatom and steric effects . However, the mechanoresponsive emission of these materials is due to crystalline-to-amorphous phase transitions.…”

Environment-Sensitive Azepane-Substituted β-Diketones and Difluoroboron Complexes with Restricted C–C Bond Rotation

“…Thus, viscochromic dyes can be used to probe lipid and cell membranes. 8,9 For example, Kuimova et al utilized a boron dipyrromethene (BODIPY) dye and fluorescence lifetime imaging microscopy (FLIM) to sense and image cell membrane viscosities. 10 In addition to dye sensitivity to solvent polarity and viscosity, dye emission can also be affected by solubility.…”

“…Such dyes possess a freely rotating bond in the structure, and after light excitation, a twisted intramolecular charge transfer (TICT) state is formed with bond rotation, leading to enhanced nonradiative decay. , In more viscous environments, enhanced emission intensity is observed due to restricted bond rotation. Thus, viscochromic dyes can be used to probe lipid and cell membranes. , For example, Kuimova et al utilized a boron dipyrromethene (BODIPY) dye and fluorescence lifetime imaging microscopy (FLIM) to sense and image cell membrane viscosities …”