Restricted Photoinduced Conformational Change in the Cu(I) Complex for Sensing Mechanical Properties

When designing photoresponsive materials, the impact of a polymer host matrix on the photophysical and photochemical properties of chromophores can be dramatic and advantageous for correlating macromolecular properties. Some compounds possess changes in their photophysical response with variation in the surrounding media (e.g., crystalline glass vs solution). This study demonstrates how changes in the excited state dynamics of [Cu(dmp)₂]⁺, where dmp = 2,9-dimethyl-1,10-phenanthroline, are used to quantitatively probe the viscosity of the surrounding polymer matrix. A correlation of both excited state lifetime and photoluminescence emission wavelength on viscosity was observed in different supramolecular materials containing [Cu(dmp)₂]⁺. These effects were attributed to restricted photoinduced structural distortion of the Cu(I) complex as the polymer matrix hardened. This photoluminescence sensor features a greater dynamic range for viscosity sensing (6 orders of magnitude) and displayed larger changes in lifetime response with respect to typical organometallic mechanosensitive probes.