Reversible mechanochromism and aggregation induced enhanced emission in phenothiazine substituted tetraphenylethylene

Mono and tetra phenothiazine (PTZ) functionalized tetraphenylethylene (TPE) derivatives PTZTPE-1 and PTZTPE-4 were designed and synthesized by the Suzuki cross-coupling reactions between PTZ boronate ester and bromo TPEs. The PTZTPE-1 and PTZTPE-4 are highly emissive in the solid state, which is crucial for a molecule to show mechanofluorochromism. The strong donor ability of PTZ could affect the donor ability of TPE leading to changes in the electronic and photophysical properties of the target molecules. The number of PTZ moieties attached to TPE could vary the twisting in the molecules, which could further affect the mechanochromic properties. The photophysical, electrochemical, solvatochromic, mechanochromic and AIE properties of PTZTPE-1 and PTZTPE-4 were studied. Both PTZTPE-1 and PTZTPE-4 show significant mechanochromic behavior and comparable spectral shift on grinding. The single crystal X-ray analysis of PTZTPE-1 reveals a twisted confirmation of PTZ and TPE phenyl rings confirming strong AIE characteristics and reversible mechanochromic behavior.