Multiple Near-Infrared Chromisms of a Heteromerous Overcrowded Ethylene with Large Permanent Dipole Moment.

An overcrowded ethylene composed of electron-donating anion, naphthoxide, and electron-accepting cation, acridinium, has been synthesized. It is in equilibrium between a folded conformer having a smaller permanent dipole moment with visible light absorption and a twisted conformer having a larger permanent dipole moment with NIR light absorption. The overcrowded ethylene shows multiple NIR chromisms, such as solvatochromism, thermochromism, mechanochromism, vapochromism, halochromism, and amphoteric electrochromisms, which are caused by the conformational change between folded and twisted conformers or by controlling the energy difference between the HOMO of the donor moiety and the LUMO of the acceptor moiety.