Mechanochromic luminescence based on a phthalonitrile-bridging salophen zinc(ii) complex

Abstract

A 4,5-diaminophthalonitrile based zinc(II)–salophen complex CN-Zn was designed and synthesized with obvious mechanochromic properties to meet application demands for stimuli-responsive luminescent materials composed of cost-efficient organometallic molecules. CN-Zn solid exhibits reversible luminescence color alteration between vibrant yellow and orange (emission maximum from λ_max = 560 nm to λ_max = 591 nm) after first being mechanically ground and then treated by organic vapor fuming. The process is repeatable and highly sensitive, which makes CN-Zn a potential sensor of both external pressure and organic volatile gases. Thermal annealing of the ground CN-Zn powder at 150 °C and 230 °C resulted in red emission (λ_max = 611 nm) and orange emission (λ_max = 599 nm), respectively. Investigations were conducted using photophysical analyses, powder X-ray diffraction (XRD), and thermal testing (DSC and TGA) to apprehend the mechanism behind the stimuli-responsive properties. The results demonstrate that external treatment can lead to a packing mode transformation between the crystalline and amorphous phase in CN-Zn, thus creating morphology dependent emission features. In view of all properties, CN-Zn is a promising option for cost-efficient stimuli-responsive materials.