Dipyrene-Terminated Oligosilanes Enable Ratiometric Fluorescence Response in Polymers toward Mechano- and Thermo-Stimuli

Here, a series of excimer-type chromophore Sin-Py (n = 1‒3) consisting of two pyrenes linked with oligosilanes of one to three silicon atoms is developed as the fluorescent motif incorporated in polymer. The fluorescence of Sin-Py is steered with the linker length where Si2-Py and Si3-Py with disilane and trisilane linkers display prominent excimer emission accompanied with pyrene monomer emission.

Covalent incorporation of Si2-Py and Si3-Py in polyurethane gives fluorescent polymers PU-Si2-Py and PU-Si3-Py, respectively, where intramolecular pyrene excimers and corresponding combined emission of excimer and monomer are obtained. Polymer films of PU-Si2-Py and PU-Si3-Py display instant and reversible ratiometric fluorescence change during uniaxial tensile test. The mechanochromic response arises from the reversible suppression of excimer formation during mechanically induced separation of the pyrene moieties and relaxation.