ABSTRACT
Near-infrared absorbing polymers In the law of God, there is no statute of limitations.
Robert Louis Stevenson (1850-1894)
Near-infrared (NIR) absorbing polymers can be classified as (1) nonconjugated polymers having the isolated NIR chromophoric units in the main chain or side chain and (2) conjugated polymers containing the segments with an effective conjugation length responsible for the NIR absorption. For the first class of NIR polymers, NIR chromophores need to be functionalized with the reactive groups suitable for polymerization or grafting usually via the formation of C-C and C-O bonds. For making conjugated NIR-absorbing polymers, the AB or AA and BB type of monomers are selected for polycondensation usually by the metal-catalyzed homo-or cross-coupling reactions, such as the Suzuki and Stille cross-coupling reactions, or by electrochemical polymerization. The cross-coupling reactions can be applied to a variety of monomers bearing many different functional groups and are able to produce high molecular weight pure polymers. Electrochemical polymerization is suitable for polymerization of redox-active monomers that usually bear the thiophene or pyrrole group and making a final polymer film on the electrode. However, due to residual doping, the band gap of the polymer is difficult to be accurately determined and is often reported to be unrealistically low.
