Near-Infrared-I to III Absorption and Emission via Core Engineering of Open-Shelled Organic Mixed-Valence Systems

Abstract

A novel class of agents is developed based on the core engineering of open-shelled organic mixed-valence (MV) systems, which enable tunable absorption and emission across the near infrared (NIR)-I to III biowindow (700-1850 nm) by adjusting the number of central nitrogen oxidation sites and the length of the conjugated bridge. Organic mixed-valence (MV) systems are synthesized through a one-step partial chemical oxidation of starburst oligoarylamines, with varying nitrogen oxidation sites and conjugated bridge lengths, including tris(4-[diethylamino]phenyl)amineⁿ⁺ (T4EPA^{n +} ), N,N,N',N'-tetrakis(4-[diisobutylamino]phenyl)-1,4-phenylenediamineⁿ⁺ (TPDA^{n +} ), and N,N,N',N'-tetrakis(4-methoxyphenyl)benzidineⁿ⁺ (TMPB^{n +} ). The absorption wavelength of the MV systems redshifted clearly as the number of central nitrogen oxidation sites increased or the conjugated bridge length is prolonged. T4EPA^{n +} with one central nitrogen oxidation site exhibits fluorescence emission in the range of 900-1400 nm, while TPDA^{n +} with two central nitrogen oxidation sites demonstrate strong heat generation capabilities. Additionally, the absorption peak of TMPB^{n +} with a biphenyl conjugated bridge reaches up to 1610 nm. Especially, these MV systems are highly stable for biological applications due to their high steric hindrance and hyperconjugation effect. These characteristics make MV systems promising candidates for constructing NIR-I/II/III emitters and photothermal agents, representing a significant advance toward developing the next generation of NIR-I to III agents.

Keywords: NIR-II emission; intervalence charge-transfer; mixed-valence systems; near-Infrared-I/II/III.