Near‐Infrared (>1000 nm) Light‐Harvesters: Design, Synthesis and Applications

Abstract

Organic molecules can absorb or emit light in UV, visible and infra‐red (IR) region of solar radiation. Fifty percent of energy of solar radiation lies in the IR region of solar spectrum and extended π‐conjugated molecules containing low optical band gap can absorb NIR radiations. Recently IR molecules have grabbed the attention of synthetic chemists. Although only few molecules have been reported so far such as derivative of BODIPY, naphthalimide, porphyrins, perylene, BBT etc., they have shown highest absorbing capacity towards greater than 1100 nm. These compounds have potential applications in different fields, such as for biomedical and optoelectronic applications. In this review, we present different classes of light‐harvesters with harvesting range above 1000 nm.

A Borondifluoride‐Complex‐Based Photothermal Agent with an 80 % Photothermal Conversion Efficiency for Photothermal Therapy in the NIR‐II Window

“…Although numbers of NIR-I absorbing molecules are successfully designed and synthesized via strengthening the D-A conjugation or expanding the polycyclic p-systems,small organic molecules with advantageous extinction ability over 1000 nm are still rare. [33] Due to the lack of suitable building blocks as well as the synthetic challenges,c urrently reported NIR-II absorbing molecules are typically limited to BBTD, [30,31,34] perylene, [35,36] porphyrin, [37,38] and cyanine [29,39,40] derivatives.T hus,i ti safundamental challenge to explore alternative building blocks to expand the library of NIR-II absorbing materials.B orondifluoride complexes with boron dipyrromethene (BODIPY) as an example,a re commonly used for constructing low band gap materials because of their strong electron-withdrawing ability. [41] Moreover, these borondifluoride-based materials usually show excellent biocompatibility,p hotostability,a nd chemostability,w hich make them potential phototherapy agents.…”

A Borondifluoride‐Complex‐Based Photothermal Agent with an 80 % Photothermal Conversion Efficiency for Photothermal Therapy in the NIR‐II Window

“…Although numbers of NIR‐I absorbing molecules are successfully designed and synthesized via strengthening the D‐A conjugation or expanding the polycyclic π‐systems, small organic molecules with advantageous extinction ability over 1000 nm are still rare [33] . Due to the lack of suitable building blocks as well as the synthetic challenges, currently reported NIR‐II absorbing molecules are typically limited to BBTD, [30, 31, 34] perylene, [35, 36] porphyrin, [37, 38] and cyanine [29, 39, 40] derivatives.…”

“…Although numbers of NIR-I absorbing molecules are successfully designed and synthesized via strengthening the D-A conjugation or expanding the polycyclic p-systems,small organic molecules with advantageous extinction ability over 1000 nm are still rare. [33] Due to the lack of suitable building blocks as well as the synthetic challenges,c urrently reported NIR-II absorbing molecules are typically limited to BBTD, [30,31,34] perylene, [35,36] porphyrin, [37,38] and cyanine [29,39,40] derivatives.T hus,i ti safundamental challenge to explore alternative building blocks to expand the library of NIR-II absorbing materials.B orondifluoride complexes with boron dipyrromethene (BODIPY) as an example,a re commonly used for constructing low band gap materials because of their strong electron-withdrawing ability. [41] Moreover, these borondifluoride-based materials usually show excellent biocompatibility,p hotostability,a nd chemostability,w hich make them potential phototherapy agents.…”

Unsymmetric Molecular Hinges Showing Intramolecular Charge Transfer Excitation: Strong Photoluminescence Properties in the Red to Near-Infrared Region Exhibited by Tri-BF2Complexes

“…Organic small-molecule red to near-infrared (NIR) fluorescent chromophores have become essential in various applications, such as organic photovoltaics, organic light-emitting diodes, biological imaging, and sensing to light harvesting. − Some traditional luminophores, such as polycyclic or macrocyclic molecules, , perylene bisimide, , porphyrin, , porphycene, − phthalocyanine, cyanine, , xanthene, − boron dipyrromethene, − and donor–acceptor dyes, ,, are common powerful red emitters. − BODIPY, as a typical boron dipyrromethene compound, stands out for its large molar absorptivity, high fluorescence, and excellent (photo)­chemical stability, making it a potential chromophore for targeting the red to NIR region via structural modification. ,− Recently, we developed a series of novel tetra-boron difluoride (tetra-BF 2 ) complexes using 2,2′-bipyrroles and 2-hydrazinopyridines or 2-hydrazinobenzothiazole in a one-pot reaction, demonstrating green-to-orange luminescence in solution, high quantum yield reaching 100%, large Stokes shift, excellent (photo)­chemical property, and efficient circularly polarized luminescence . The chromophores that were produced are symmetric and highly fluorescent compounds consisting of four different bidentate binding pockets based on 2,2′-bipyrrole to provide four BF 2 moieties in the structures after BF 2 complexation (Figure ).…”