A slippery molecular assembly allows water as a self-erasable security marker

Abstract

Protection of currency and valuable documents from counterfeit continues to be a challenge. While there are many embedded security features available for document safety, they are not immune to forgery. Fluorescence is a sensitive property, which responds to external stimuli such as solvent polarity, temperature or mechanical stress, however practical use in security applications is hampered due to several reasons. Therefore, a simple and specific stimuli responsive security feature that is difficult to duplicate is of great demand. Herein we report the design of a fluorescent molecular assembly on which water behaves as a self-erasable security marker for checking the authenticity of documents at point of care. The underlying principle involves the disciplined self-assembly of a tailor-made fluorescent molecule, which initially form a weak blue fluorescence (λem = 425 nm, Φf = 0.13) and changes to cyan emission (λem = 488 nm,Φf = 0.18) in contact with water due to a reversible molecular slipping motion. This simple chemical tool, based on the principles of molecular self-assembly and fluorescence modulation, allows creation of security labels and optically masked barcodes for multiple documents authentication.

An unprecedented amplification of near-infrared emission in a Bodipy derived π-system by stress or gelation

“…4a ). 7b , 14 In addition, several weak signals were seen in the range of 2 θ = 10–30°, indicating a lesser extent of π-stacking ( Fig. 4a inset).…”

“…4b ) with a sharp peak at 2 θ = 2.25° ( d -spacing = 39.6 Å). 7b , 14 A comparison of the diffraction peaks of the xerogel with the n -decane film before and after shearing at the wide-angle region of 10–30° is shown in Fig. 4c .…”

“…S15 † ), indicating 1-D supramolecular polymer formation through amide H-bonding. 11f , 14 , 15 Shearing resulted in the rupture of the amide H-bonding which is clear from the appearance of the 3421 cm –1 band.…”

Tunable Electrochromic Luminescence of Iridium(III) Complexes for Information Self‐Encryption and Anti‐Counterfeiting

“…The obtained complexes were characterized by nuclear magnetic resonance (NMR) and matrix-assisted laser desorption ionization time-of-fl ight mass spectrometry, cyclic voltammetry, UV/Vis absorption spectrometry, and steady-state and transientstate photoluminescence spectrometry Complexes Ir1 − Ir4 exhibit tunable emission colors from green to red in CH 3 CN solution (Figure 1 , middle), which are dependent on the C^N ligands. [17][18][19][20] The electric fi eld has been widely applied as an important external stimulus in many optoelectronic devices, because it is very convenient to handle. [ 15,16 ] These stimuli can induce signifi cant changes in various intrinsic physical properties of the materials, including absorption, photoluminescence, conductivity, ferroelectricity, magnetism polarity, and phase state, rendering the materials good candidates for information recording and storage devices.…”

Molecular modelling of supramolecular one dimensional polymers

“…Commercial exploitation of supramolecular polymers use the advantage of reversibility and responsiveness, specically in adhesives, printing, cosmetics, personal care, and coatings [5][6][7] and in many bio-medical applications. [8][9][10][11][12][13][14][15][16][17][18][19][20] The mechanism of self-assembly of molecules in solution can be broadly classied into two categories based on the dependence of the association constant K, between species on oligomer size. 21 These are isodesmic and cooperative mechanisms.…”