Synthesis of a New Series of Organic Solid-State Near-Infrared Emitters: The Role of Crystal Packing and Weak Intermolecular Interactions and Application in Latent Fingerprint Detection

Abstract

The development of novel metal-free solid-state near-infrared (NIR) emitters is a challenging task. Herein, the facile synthesis of two organic solid-state NIR emitters emitting at 705 and 673 nm are reported. The mechanism of NIR emission is shown to be an excited-state intramolecular proton transfer through a series of experiments as well as theoretical calculations. X-ray crystallography analyses revealed that the unique solid-state packing arrangement of the molecules with a slipped face-to-face arrangement helps to prevent the π−π stacking interaction and prevent aggregation-caused quenching in these molecules. A Hirshfeld analysis was performed to quantify the contribution of intra-and intermolecular interactions to the supramolecular assembly. Appropriate control compounds were synthesized, and their fluorescence and structural aspects have been studied to confirm the proposed NIR emission mechanism. These new solid-state NIR emitters have been tested as latent fingerprint (LFP) imaging probes on a variety of porous and nonporous surfaces including aluminum foil, glass, ceramic tile, wooden surface, and stainless steel using a powder dusting approach. High-quality LFP images with high selectivity, sensitivity, contrast, and low background interference were obtained using these probes with the clear identification of up to 16 characterizable level 2 and level 3 features.

Mono- and Rare Trinuclear Zn(II) Complexes with Near-Infrared Emissive Ligands: Anion-Responsive Nuclearity Control, Interconversion, Solid-State NIR Emission, and Latent Fingerprint Imaging

“…Among the mononuclear complexes, M2 exhibited the highest PLQY, and M3 showed the lowest PLQY, which may be attributed partly to the efficient ILCT from the −OMe group in M2 and the spin−orbit coupling effect of the heavier −Br moiety in M3, respectively. 6,52 An enhancement in the quantum efficiency of the mononuclear complexes compared to their ligands 23 was observed, which may be due to the comparatively lower dihedral angles exhibited by the complexes between the planes of their aromatic rings. A lower dihedral angle enhances the planarity and π-electron delocalization, possibly contributing to higher fluorescence efficiency.…”

“…The synthesis and characterization of HL1 and HL2 have been reported earlier. 23 The synthesis, characterization, and single-crystal Xray data of HL3 are given in the Supporting Information.…”

Organic Near‐Infrared Luminescent Materials Based on Excited State Intramolecular Proton Transfer Process†

“…prepared novel organic solid‐state NIR emitters 1AA (compound 15 ) and 1A (compound 16 ) with ESIPT phenomenon by Schiff base reaction. [ 68‐69 ] Due to the presence of Schiff bases, 1A and 1AA can produce photoinduced electron transfer (PET) phenomenon, which affects their fluorescence properties. However, one of the two arms of 1AA and 1A (the D1 arm) exhibits a strong intramolecular hydrogen bond interaction between the phenol‐OH and the imine N, which allows the ESIPT phenomenon to occur and prevent the PET.…”

Thermally Activated Delayed Fluorescence Emitters with Intramolecular Proton Transfer for High Luminance Solution-Processed Organic Light-Emitting Diodes

“…The asymmetric unit consists of one molecule of TPXZBM (Figure 2, Figure S25, and Table S2). The dihedral angles between the bridging phenyl rings and the mean planes of the PXZ donor moieties are 65.95 (15), 64.49 (13), and 75.98(15)°, indicating a highly twisted structure. A similar set of dihedral angles between PXZ units and bridging phenyl groups was also observed in PXZPDO.…”

“…ESIPT luminescence is thus characterized by large changes in the Stokes shift and an emission that can be tunable by the local environment. − A potential consequence of ESIPT is that the electron density distribution of the frontier molecular orbitals can change significantly between the two tautomeric forms, leading to changes in Δ E ST , which will then affect the efficiency of TADF. Because of these unique photophysical properties, ESIPT molecules are attractive for fluorescence sensing, bioimaging, NIR emitters, UV absorbers, and for lighting materials. − Additionally, a small number of reports exist that employ ESIPT-based fluorophores as emitters in OLEDs (Chart ); ,− however, the performance of these devices is poor, in part due to the inefficient harvesting of excitons. The first report of a molecule ( HPI-Ac ) exhibiting both ESIPT and TADF dates back to 2007; however, no OLEDs were fabricated .…”