A Supramolecular Nanocomposite as a Near‐Infrared‐Transmitting Optical Filter for Security and Forensic Applications

Abstract

Visibly opaque but near-infrared (NIR)-transparent materials are an essential component for night-vision photography, security imaging, and forensic applications. Herein, the development of a novel supramolecular black dye from a diketopyrrolopyrrole (DPP)-based low-molecular-weight organogelator is described. In the solution state, the monomer of DPP-Amide exhibits a deep green color with a broad absorption in the visible region due to firm intramolecular charge transfer from the donor to the acceptor unit. Interestingly, due to the synergistic effect of H-bonding and π-stacking, DPP-Amide can form a black organogel in toluene with complete spectral coverage from 300 to 800 nm, and transmits beyond 850 nm. In the gel state, complete visible-spectrum coverage is achieved due to the simultaneous formation of both H- and J-type aggregates, which is confirmed via absorption studies. To create a free-standing NIR-transmitting elastomeric black filter, nanoscopic molecular aggregates of DPP-Amide (0.15 wt%) are embedded into a poly(dimethylsiloxane) matrix. This nanocomposite possesses high NIR transparency with good thermal and photostability for practical applications. Finally, the use of the developed material for NIR photography, security, and forensic-related applications is demonstrated.

A Hybrid Organogel of a Low Band Gap Diketopyrrolopyrrole with PC71BM: Phase Separated Morphology and Enhanced Photoconductivity

“…Under moderate concentration ( c =1.2×10 −4 M) of DPP‐Amide in toluene, in addition to monomer bands, presence of a new band at 773 nm was observed due to molecular aggregation. Furthermore, in the gel state, DPP‐Amide exhibited hypsochromically and bathochromically shifted absorption bands with respect to the monomer, indicating the formation of both H‐ and J‐aggregates ,,,. Reversibility of the aggregates was confirmed by variable temperature UV‐Vis spectral studies of DPP‐Amide in toluene ( c =1.2×10 −4 M) (Figure S2).…”

“…We have synthesized an A−D−A−D−A based small molecule, abbreviated as DPP‐Amide (Scheme a) having terminal H‐bonding groups that can self−assemble in toluene, leading to the formation of a black organogel. In a recent communication, we have used this organogel to make an opaque but NIR transparent flexible optical filters . In this work, we report the morphological features and the photoconductivity of the hybrid‐assembly of DPP‐Amide with PC 71 BM (Scheme a and b).…”

“…Figure a shows the normalized absorption spectra of the DPP‐Amide in monomer, aggregate and gel states. At very low concentrations, two distinct absorption bands, one at ∼ 428 nm, which arise due to π‐π* transition and a broad absorption with a maximum at ∼ 628 nm due to firm internal charge transfer from the donor to acceptor unit were observed . Extended conjugation results in broad absorption from 300–750 nm with an optical band gap of 1.61 eV.…”

“…DPP‐Amide and DPP‐Ester were prepared by Knoevenagel condensation between 5′,5′′‐(2,5‐didodecyl‐3,6‐dioxo‐2,3,5,6‐tetrahydropyrrolo[3, 4‐ c ]pyrrole‐1,4‐diyl)di‐2,2′‐bithiophene‐5‐carbaldehyde ( DPP‐3 ) and the corresponding active methylene derivative (Scheme S1). The synthesis of DPP‐3 was carried out via known synthetic procedures (see Supporting Information) . All compounds were characterized by FT‐IR, 1 H and 13 C NMR, mass and elemental analyses.…”

Self-Assembly of Bodipy-Derived Extended π-Systems

“…In addition, molecular self-assembly including gelation can also be considered to be an alternative approach towards the modulation of emission wavelength. 60,61 In recent times, NIR emitting Bodipy-derived soft materials based on the self-assembly process have been reported. 6265 For instance, the π-extended Bodipy derivative 1 ( Figure 2) exhibited absorption maxima at 370 and 646 nm and a fluorescence maximum at 669 nm in THF.…”