Rational Design, Synthesis, and Optical Properties of Film‐Forming, Near‐Infrared Absorbing, and Fluorescent Chromophores with Multidonors and Large Heterocyclic Acceptors

Abstract

A new series of film-forming, low-bandgap chromophores (1 a,b and 2 a,b) were rationally designed with aid of a computational study, and then synthesized and characterized. To realize absorption and emission above the 1000 nm wavelength, the molecular design focuses on lowering the LUMO level by fusing common heterocyclic units into a large conjugated core that acts an electron acceptor and increasing the charge transfer by attaching the multiple electron-donating groups at the appropriate positions of the acceptor core. The chromophores have bandgap levels of 1.27-0.71 eV, and accordingly absorb at 746-1003 nm and emit at 1035-1290 nm in solution. By design, the relatively high molecular weight (up to 2400 g mol(-1)) and non-coplanar structure allow these near-infrared (NIR) chromophores to be readily spin-coated as uniform thin films and doped with other organic semiconductors for potential device applications. Doping with [6,6]-phenyl-C(61) butyric acid methyl ester leads to a red shift in the absorption only for 1 a and 2 a. An interesting NIR electrochromism was found for 2 a, with absorption being turned on at 1034 nm when electrochemically switched (at 1000 mV) from its neutral state to a radical cation state. Furthermore, a large Stokes shift (256-318 nm) is also unique for this multidonor-acceptor type of chromophore, indicating a significant structural difference between the ground state and the excited state. Photoluminescence of the film of 2 a was further probed at variable temperatures and the results strongly suggest that the restriction of bond rotations certainly helps to diminish non-radiative decay and thus enhance the luminescence of these large chromophores.

Near‐Infrared Organic Compounds and Emerging Applications

“…The spacer unit between the donor and acceptor also plays an important role in controlling the energy gap of organic compounds, because it can change the interaction of electronic orbitals of donor and acceptor 26. In addition, the D–A charge transfer interaction can be further enhanced by attaching multiple electron‐donating groups at the appropriate positions of the acceptor or with different donor–acceptor topology 27…”

Organic Ambipolar Conjugated Molecules for Electronics: Synthesis and Structure–Property Relationships

“…[20,21] core ( Figure 6). [28] To clarify and suppress the long wavelength in fluorenebased EL blue materials, [29] Hsu et al have tethered gold nanoparticles to the side chains of 32 through its ArSCH 3 anchor groups ( Figure 7). The presence of 1 wt.-% of the tethered gold nanoparticles led to a reduction in the degree of aggregation of the polymer chains, resulting in a 50% increase in its quantum yield.…”

Mono‐ and Polyazatriphenylene‐Based Ligands: An Updated Library of Synthetic Strategies (2001–2018)

“…Wang et al synthesized four azatriphenylene derivatives as film‐forming, near‐IR absorbing and fluorescent chromophores (Scheme ) . The starting materials ( 116 ) were obtained by a Stille coupling reaction between 4,7‐dibromo‐5,6‐dinitro‐2,1,3‐benzothiadiazole and tributyltin derivatives .…”