The change in emission wavelength of a fluorophore in response to a mechanical stimulus is referred to as mechanochromic luminescence (ML).  ML materials are responsive materials with diverse properties that are suitable for applications ranging from luminescent switches and mechanosensors, to optoelectronic devices and data storage. One class of mechanochromic material, previously reported by Fraser et al., are difluoroboron  �-diketonate complexes (BF2bdks) that exhibit tunable emission in solution as well as in the solid state.  Furthermore, the ML is reversible at room temperature.  Perturbed regions recover their original blueshifted emission and can be smeared again many times. It is also possible to generate dark images via mechanochromic luminescence quenching (MLQ) through heavy atom substitution (e.g. iodide). In order to better understand the effects of electron donation and heavy atom substitution, dinaphthoylmethane ligands (dnm) with bromide and methoxy substituents were synthesized.  Surprisingly, dnm ligands show visible ML absent coordination to the Lewis acidic difluoroboron. Dnm ligands have other interesting optical properties, including aggregation induced emission (AIE) and one derivative can be isolated in three distinct forms, each with unique optical properties. Optical properties of both dnm ligands and their boron complexes were investigated in solution and in the solid state.  ML was studied for thin films on both glass and paper substrates, and AIE was explored by measuring the emission of each fluorophore in various THF/H2O mixtures.  With acidic protons and an open coordination site, diketone ligand derivatives present opportunities for pH and ion detection in addition to mechanosensing.

Mechanochromic luminescence and aggregation induced emission of naphthyl �-diketones and their boron difluoride complexes

247th National Meeting (2014)

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