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

Thirumalai R, Mukhopadhyay RD, Praveen VK, Ajayaghosh A - Sci Rep (2015)

Bottom Line: While there are many embedded security features available for document safety, they are not immune to forgery.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.

View Article: PubMed Central - PubMed

Affiliation: Photosciences and Photonics Group, Chemical Sciences and Technology Division, CSIR-National Institute for Interdisciplinary Science and Technology (CSIR-NIIST), Trivandrum 695019, India.

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.

No MeSH data available.


Related in: MedlinePlus

Mechanism of the fluorescence change based on molecular packing.(a) SAXS pattern of PE1 in the (i) absence and (ii) presence of water, (iii) PE2 and (iv) PE3. The corresponding molecular arrangements are shown on the top of the SAXS patterns. (b) Schematic illustration of sliding of the PE1 molecule in the absence and presence of water on paper surface. Disruption of H-bonds and the breathing of the oxyethylene chains in presence of water experience an inward pushing of the molecules resulting in the change of an H-type (B-phase) to J-type (C-phase) packing. The images in panel ‘b’ (right) show the zoomed portion of the molecular arrangement illustrating the H-bond breaking and molecular sliding (arrows show the direction of sliding).
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f5: Mechanism of the fluorescence change based on molecular packing.(a) SAXS pattern of PE1 in the (i) absence and (ii) presence of water, (iii) PE2 and (iv) PE3. The corresponding molecular arrangements are shown on the top of the SAXS patterns. (b) Schematic illustration of sliding of the PE1 molecule in the absence and presence of water on paper surface. Disruption of H-bonds and the breathing of the oxyethylene chains in presence of water experience an inward pushing of the molecules resulting in the change of an H-type (B-phase) to J-type (C-phase) packing. The images in panel ‘b’ (right) show the zoomed portion of the molecular arrangement illustrating the H-bond breaking and molecular sliding (arrows show the direction of sliding).

Mentions: For an insight on the mechanism of the water induced fluorescence colour change, we performed film state small angle X-ray scattering (SAXS) analysis of the PE1 molecular assembly before and after exposing to water. These data are compared with X-ray diffraction pattern of PE2 and PE3. The initial blue emitting film of PE1 (Fig. 5a, i) showed two sharp diffraction patterns at 42.5 and 21.6 Å, which are assigned to an H-type molecular arrangement. The 42.5 Å peak corresponds to the width of a single one-dimensional (1-D) layer of the molecules and the 21.6 Å peak corresponds to the rigid rod PE moiety. In THF, the emission arises from excitation of the monomer band at the 310–350 nm region. In the case of the film state, a strong blue shift in the excitation with red shift in emission was observed (Supplementary Fig. S22) indicating the formation of fluorescent H-type aggregates. After spraying water, the cyan emitting film showed four sharp diffractions 41.3, 37.5, 24.8 and 21.8 Å of varying intensities (Fig. 5a, ii). These peaks indicate the sliding of the molecules in the presence of water3536 as depicted in (Fig. 5b, Supplementary Movie S4). The diffraction peak corresponding 24.8 Å may be associated with the slipped packing of the rigid PE moiety and 41.3 Å can be assigned to the total width of the 1-D assembly. The 21.8 and 37.5 Å peaks are assigned to the rigid PE part and the total length of the PE1 molecule respectively. After complete removal of water, the regenerated blue emitting film exhibited the original X-ray pattern revealing the sliding back of the assembly to its original form. The X-ray diffraction pattern of PE2 film (Fig. 5a, iii) showed four different peaks (42.6, 35.2, 26.6 and 22.5 Å) almost similar to that of the PE1 film after water treatment, indicating identical slipped molecular packing. This slipped packing is formed due to the absence of hydrogen bonding amide groups in PE2. On the other hand, the PE3 molecule (Fig. 5a, iv) having the alkyl chain exhibited diffraction patterns (42.1 and 22.5 Å) identical to that of the blue PE1 film indicating the formation of hydrogen bonded H-type 1-D assembly in the film state.


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

Thirumalai R, Mukhopadhyay RD, Praveen VK, Ajayaghosh A - Sci Rep (2015)

Mechanism of the fluorescence change based on molecular packing.(a) SAXS pattern of PE1 in the (i) absence and (ii) presence of water, (iii) PE2 and (iv) PE3. The corresponding molecular arrangements are shown on the top of the SAXS patterns. (b) Schematic illustration of sliding of the PE1 molecule in the absence and presence of water on paper surface. Disruption of H-bonds and the breathing of the oxyethylene chains in presence of water experience an inward pushing of the molecules resulting in the change of an H-type (B-phase) to J-type (C-phase) packing. The images in panel ‘b’ (right) show the zoomed portion of the molecular arrangement illustrating the H-bond breaking and molecular sliding (arrows show the direction of sliding).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4419532&req=5

f5: Mechanism of the fluorescence change based on molecular packing.(a) SAXS pattern of PE1 in the (i) absence and (ii) presence of water, (iii) PE2 and (iv) PE3. The corresponding molecular arrangements are shown on the top of the SAXS patterns. (b) Schematic illustration of sliding of the PE1 molecule in the absence and presence of water on paper surface. Disruption of H-bonds and the breathing of the oxyethylene chains in presence of water experience an inward pushing of the molecules resulting in the change of an H-type (B-phase) to J-type (C-phase) packing. The images in panel ‘b’ (right) show the zoomed portion of the molecular arrangement illustrating the H-bond breaking and molecular sliding (arrows show the direction of sliding).
Mentions: For an insight on the mechanism of the water induced fluorescence colour change, we performed film state small angle X-ray scattering (SAXS) analysis of the PE1 molecular assembly before and after exposing to water. These data are compared with X-ray diffraction pattern of PE2 and PE3. The initial blue emitting film of PE1 (Fig. 5a, i) showed two sharp diffraction patterns at 42.5 and 21.6 Å, which are assigned to an H-type molecular arrangement. The 42.5 Å peak corresponds to the width of a single one-dimensional (1-D) layer of the molecules and the 21.6 Å peak corresponds to the rigid rod PE moiety. In THF, the emission arises from excitation of the monomer band at the 310–350 nm region. In the case of the film state, a strong blue shift in the excitation with red shift in emission was observed (Supplementary Fig. S22) indicating the formation of fluorescent H-type aggregates. After spraying water, the cyan emitting film showed four sharp diffractions 41.3, 37.5, 24.8 and 21.8 Å of varying intensities (Fig. 5a, ii). These peaks indicate the sliding of the molecules in the presence of water3536 as depicted in (Fig. 5b, Supplementary Movie S4). The diffraction peak corresponding 24.8 Å may be associated with the slipped packing of the rigid PE moiety and 41.3 Å can be assigned to the total width of the 1-D assembly. The 21.8 and 37.5 Å peaks are assigned to the rigid PE part and the total length of the PE1 molecule respectively. After complete removal of water, the regenerated blue emitting film exhibited the original X-ray pattern revealing the sliding back of the assembly to its original form. The X-ray diffraction pattern of PE2 film (Fig. 5a, iii) showed four different peaks (42.6, 35.2, 26.6 and 22.5 Å) almost similar to that of the PE1 film after water treatment, indicating identical slipped molecular packing. This slipped packing is formed due to the absence of hydrogen bonding amide groups in PE2. On the other hand, the PE3 molecule (Fig. 5a, iv) having the alkyl chain exhibited diffraction patterns (42.1 and 22.5 Å) identical to that of the blue PE1 film indicating the formation of hydrogen bonded H-type 1-D assembly in the film state.

Bottom Line: While there are many embedded security features available for document safety, they are not immune to forgery.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.

View Article: PubMed Central - PubMed

Affiliation: Photosciences and Photonics Group, Chemical Sciences and Technology Division, CSIR-National Institute for Interdisciplinary Science and Technology (CSIR-NIIST), Trivandrum 695019, India.

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.

No MeSH data available.


Related in: MedlinePlus