Design strategies and recent results for near-infrared-emissive materials based on element-block χ-conjugated polymers

Abstract

The significance of NIR light-absorbing and/or emitting materials is growing day by day in industrial applications as well as research fields because of intrinsic versatility of NIR light. The unique properties of NIR light, such as invisibility to human eyes, high permeability and transmissibility, are readily applicable to novel functional devices for detection sensors, optical communications, imaging probes and photomedical therapy. However, there are several problems to be overcome especially for obtaining efficient NIR-emissive materials, and therefore development of new skeletons which can present efficient NIR emission is still challenging. Herein, we demonstrate molecular design strategies and recent results for preparing the NIR-emissive materials based on element-block π-conjugated polymers. By focusing on the isolated lowest molecular orbital (LUMO), selective perturbation of one frontier molecular orbital (FMO) is accomplished, leading to narrow-energy-gap materials without expanding π-conjugated systems. As another example, it is shown that hypervalent bonds of main group elements are also effective for narrowing energy gap to generate emission in the NIR region. It can be said that the combination of the inherent element features with π-conjugated polymeric systems is expected to be one solution to overcome these problems. On the basis of this strategy, we obtained a variety of π-conjugated polymers showing light-absorption and/or emission in the NIR region with versatile functions. Our approaches presented in these recent studies could be new tactics for developing next-generation optical materials with NIR-light absorption and/or emission.