Abstract

Zn2+ and Cu2+ complexation of cyclam-triazolyl-naphthalimide fluoro-ionophores lead to increased and decreased fluorescence respectively. The differences between the two metals are accounted for by their Lewis acid and base properties. This difference means the system can be described as an optical diode with characteristics that suggest measurable differences in fluorescence rise and decay times for the mechanical suppression of bend- and/or twist-induced emissions from intramolecular charge transfer. Different fluorescence evolution profiles are observed offering a new way of distinguishing metal ions for applications in biomedical and environmental sensing.

© 2015 Optical Society of America

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References

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  1. J. M. Tour, “Molecular electronics. Synthesis and testing of components,” Acc. Chem. Res. 33(11), 791–804 (2000).
    [Crossref] [PubMed]
  2. A. H. Flood, J. F. Stoddart, D. W. Steuerman, and J. R. Heath, “Chemistry. Whence molecular electronics?” Science 306(5704), 2055–2056 (2004).
    [Crossref] [PubMed]
  3. H. B. Akkerman, P. W. M. Blom, D. M. de Leeuw, and B. de Boer, “Towards molecular electronics with large-area molecular junctions,” Nature 441(7089), 69–72 (2006).
    [Crossref] [PubMed]
  4. I. Salzmann and G. Heimel, “Towards a comprehensive understanding of molecular doping organic semiconductors,” J. Electron Spectrosc. Relat. Phenom.In press., doi:.
    [Crossref]
  5. L. De Sio, T. Placido, R. Comparelli, M. L. Curri, M. Striccoli, N. Tabiryan, and T. J. Bunning, “Next-generation thermo-plasmonic technologies and plasmonic nanoparticles in optoelectronics,” Progress in Quant. Electron. 41, 23–70 (2015).
  6. C. J. Lambert, “Basic concepts of quantum interference and electron transport in single-molecule electronics,” Chem. Soc. Rev. 44(4), 875–888 (2015).
    [Crossref] [PubMed]
  7. D. Sareen, P. Kaur, and K. Singh, “Strategies in detection of metal ions using dyes,” Coord. Chem. Rev. 265, 125–154 (2014).
    [Crossref]
  8. E. Lippert, W. Luder, F. Moll, H. Naggele, H. Boos, H. Prigge, and I. Siebold-Blankenstein, “Transformation of electron excitation energy,” Angew. Chem. 73, 695–706 (1961).
    [Crossref]
  9. W. Rettig, “Charge separation in excited states of decoupled systems-TICT compounds and implications regarding the development of new laser dyes and the primary process,” Angew. Chem. Int. Ed. Engl. 25(11), 971–988 (1986).
    [Crossref]
  10. K. Rotkiewicz, K. H. Grellman, and Z. R. Grabowski, “Reinterpretation of the anomalous fluorescense of pn, n-dimethylamino-benzonitrile,” Chem. Phys. Lett. 19(3), 315–318 (1973).
    [Crossref]
  11. S. Aoki, D. Kagata, M. Shiro, K. Takeda, and E. Kimura, “Metal chelation-controlled twisted intramolecular charge transfer and its application to fluorescent sensing of metal ions and anions,” J. Am. Chem. Soc. 126(41), 13377–13390 (2004).
    [Crossref] [PubMed]
  12. S. Ast, P. J. Rutledge, and M. H. Todd, “Reversing the Triazole Topology in a Cyclam‐Triazole‐Dye Ligand Gives a 10‐Fold Brighter Signal Response to Zn2+ in Aqueous Solution,” Eur. J. Inorg. Chem. 2012(34), 5611–5615 (2012).
    [Crossref]
  13. S. Ast, S. Kuke, P. J. Rutledge, and M. H. Todd, “Using click chemistry to Tune the Properties and the Fluorescence Response Mechanism of Structurally Similar Probes for Metal Ions,” Eur. J. Inorg. Chem. 2015(1), 58–66 (2015).
    [Crossref]
  14. M. Arafat Hossain, J. Canning, S. Ast, K. Cook, P. J. Rutledge, and A. Jamalipour, “Combined “dual” absorption and fluorescence smartphone spectrometers,” Opt. Lett. 40(8), 1737–1740 (2015).
    [Crossref] [PubMed]

2015 (4)

L. De Sio, T. Placido, R. Comparelli, M. L. Curri, M. Striccoli, N. Tabiryan, and T. J. Bunning, “Next-generation thermo-plasmonic technologies and plasmonic nanoparticles in optoelectronics,” Progress in Quant. Electron. 41, 23–70 (2015).

C. J. Lambert, “Basic concepts of quantum interference and electron transport in single-molecule electronics,” Chem. Soc. Rev. 44(4), 875–888 (2015).
[Crossref] [PubMed]

S. Ast, S. Kuke, P. J. Rutledge, and M. H. Todd, “Using click chemistry to Tune the Properties and the Fluorescence Response Mechanism of Structurally Similar Probes for Metal Ions,” Eur. J. Inorg. Chem. 2015(1), 58–66 (2015).
[Crossref]

M. Arafat Hossain, J. Canning, S. Ast, K. Cook, P. J. Rutledge, and A. Jamalipour, “Combined “dual” absorption and fluorescence smartphone spectrometers,” Opt. Lett. 40(8), 1737–1740 (2015).
[Crossref] [PubMed]

2014 (1)

D. Sareen, P. Kaur, and K. Singh, “Strategies in detection of metal ions using dyes,” Coord. Chem. Rev. 265, 125–154 (2014).
[Crossref]

2012 (1)

S. Ast, P. J. Rutledge, and M. H. Todd, “Reversing the Triazole Topology in a Cyclam‐Triazole‐Dye Ligand Gives a 10‐Fold Brighter Signal Response to Zn2+ in Aqueous Solution,” Eur. J. Inorg. Chem. 2012(34), 5611–5615 (2012).
[Crossref]

2006 (1)

H. B. Akkerman, P. W. M. Blom, D. M. de Leeuw, and B. de Boer, “Towards molecular electronics with large-area molecular junctions,” Nature 441(7089), 69–72 (2006).
[Crossref] [PubMed]

2004 (2)

S. Aoki, D. Kagata, M. Shiro, K. Takeda, and E. Kimura, “Metal chelation-controlled twisted intramolecular charge transfer and its application to fluorescent sensing of metal ions and anions,” J. Am. Chem. Soc. 126(41), 13377–13390 (2004).
[Crossref] [PubMed]

A. H. Flood, J. F. Stoddart, D. W. Steuerman, and J. R. Heath, “Chemistry. Whence molecular electronics?” Science 306(5704), 2055–2056 (2004).
[Crossref] [PubMed]

2000 (1)

J. M. Tour, “Molecular electronics. Synthesis and testing of components,” Acc. Chem. Res. 33(11), 791–804 (2000).
[Crossref] [PubMed]

1986 (1)

W. Rettig, “Charge separation in excited states of decoupled systems-TICT compounds and implications regarding the development of new laser dyes and the primary process,” Angew. Chem. Int. Ed. Engl. 25(11), 971–988 (1986).
[Crossref]

1973 (1)

K. Rotkiewicz, K. H. Grellman, and Z. R. Grabowski, “Reinterpretation of the anomalous fluorescense of pn, n-dimethylamino-benzonitrile,” Chem. Phys. Lett. 19(3), 315–318 (1973).
[Crossref]

1961 (1)

E. Lippert, W. Luder, F. Moll, H. Naggele, H. Boos, H. Prigge, and I. Siebold-Blankenstein, “Transformation of electron excitation energy,” Angew. Chem. 73, 695–706 (1961).
[Crossref]

Akkerman, H. B.

H. B. Akkerman, P. W. M. Blom, D. M. de Leeuw, and B. de Boer, “Towards molecular electronics with large-area molecular junctions,” Nature 441(7089), 69–72 (2006).
[Crossref] [PubMed]

Aoki, S.

S. Aoki, D. Kagata, M. Shiro, K. Takeda, and E. Kimura, “Metal chelation-controlled twisted intramolecular charge transfer and its application to fluorescent sensing of metal ions and anions,” J. Am. Chem. Soc. 126(41), 13377–13390 (2004).
[Crossref] [PubMed]

Arafat Hossain, M.

Ast, S.

M. Arafat Hossain, J. Canning, S. Ast, K. Cook, P. J. Rutledge, and A. Jamalipour, “Combined “dual” absorption and fluorescence smartphone spectrometers,” Opt. Lett. 40(8), 1737–1740 (2015).
[Crossref] [PubMed]

S. Ast, S. Kuke, P. J. Rutledge, and M. H. Todd, “Using click chemistry to Tune the Properties and the Fluorescence Response Mechanism of Structurally Similar Probes for Metal Ions,” Eur. J. Inorg. Chem. 2015(1), 58–66 (2015).
[Crossref]

S. Ast, P. J. Rutledge, and M. H. Todd, “Reversing the Triazole Topology in a Cyclam‐Triazole‐Dye Ligand Gives a 10‐Fold Brighter Signal Response to Zn2+ in Aqueous Solution,” Eur. J. Inorg. Chem. 2012(34), 5611–5615 (2012).
[Crossref]

Blom, P. W. M.

H. B. Akkerman, P. W. M. Blom, D. M. de Leeuw, and B. de Boer, “Towards molecular electronics with large-area molecular junctions,” Nature 441(7089), 69–72 (2006).
[Crossref] [PubMed]

Boos, H.

E. Lippert, W. Luder, F. Moll, H. Naggele, H. Boos, H. Prigge, and I. Siebold-Blankenstein, “Transformation of electron excitation energy,” Angew. Chem. 73, 695–706 (1961).
[Crossref]

Bunning, T. J.

L. De Sio, T. Placido, R. Comparelli, M. L. Curri, M. Striccoli, N. Tabiryan, and T. J. Bunning, “Next-generation thermo-plasmonic technologies and plasmonic nanoparticles in optoelectronics,” Progress in Quant. Electron. 41, 23–70 (2015).

Canning, J.

Comparelli, R.

L. De Sio, T. Placido, R. Comparelli, M. L. Curri, M. Striccoli, N. Tabiryan, and T. J. Bunning, “Next-generation thermo-plasmonic technologies and plasmonic nanoparticles in optoelectronics,” Progress in Quant. Electron. 41, 23–70 (2015).

Cook, K.

Curri, M. L.

L. De Sio, T. Placido, R. Comparelli, M. L. Curri, M. Striccoli, N. Tabiryan, and T. J. Bunning, “Next-generation thermo-plasmonic technologies and plasmonic nanoparticles in optoelectronics,” Progress in Quant. Electron. 41, 23–70 (2015).

de Boer, B.

H. B. Akkerman, P. W. M. Blom, D. M. de Leeuw, and B. de Boer, “Towards molecular electronics with large-area molecular junctions,” Nature 441(7089), 69–72 (2006).
[Crossref] [PubMed]

de Leeuw, D. M.

H. B. Akkerman, P. W. M. Blom, D. M. de Leeuw, and B. de Boer, “Towards molecular electronics with large-area molecular junctions,” Nature 441(7089), 69–72 (2006).
[Crossref] [PubMed]

De Sio, L.

L. De Sio, T. Placido, R. Comparelli, M. L. Curri, M. Striccoli, N. Tabiryan, and T. J. Bunning, “Next-generation thermo-plasmonic technologies and plasmonic nanoparticles in optoelectronics,” Progress in Quant. Electron. 41, 23–70 (2015).

Flood, A. H.

A. H. Flood, J. F. Stoddart, D. W. Steuerman, and J. R. Heath, “Chemistry. Whence molecular electronics?” Science 306(5704), 2055–2056 (2004).
[Crossref] [PubMed]

Grabowski, Z. R.

K. Rotkiewicz, K. H. Grellman, and Z. R. Grabowski, “Reinterpretation of the anomalous fluorescense of pn, n-dimethylamino-benzonitrile,” Chem. Phys. Lett. 19(3), 315–318 (1973).
[Crossref]

Grellman, K. H.

K. Rotkiewicz, K. H. Grellman, and Z. R. Grabowski, “Reinterpretation of the anomalous fluorescense of pn, n-dimethylamino-benzonitrile,” Chem. Phys. Lett. 19(3), 315–318 (1973).
[Crossref]

Heath, J. R.

A. H. Flood, J. F. Stoddart, D. W. Steuerman, and J. R. Heath, “Chemistry. Whence molecular electronics?” Science 306(5704), 2055–2056 (2004).
[Crossref] [PubMed]

Heimel, G.

I. Salzmann and G. Heimel, “Towards a comprehensive understanding of molecular doping organic semiconductors,” J. Electron Spectrosc. Relat. Phenom.In press., doi:.
[Crossref]

Jamalipour, A.

Kagata, D.

S. Aoki, D. Kagata, M. Shiro, K. Takeda, and E. Kimura, “Metal chelation-controlled twisted intramolecular charge transfer and its application to fluorescent sensing of metal ions and anions,” J. Am. Chem. Soc. 126(41), 13377–13390 (2004).
[Crossref] [PubMed]

Kaur, P.

D. Sareen, P. Kaur, and K. Singh, “Strategies in detection of metal ions using dyes,” Coord. Chem. Rev. 265, 125–154 (2014).
[Crossref]

Kimura, E.

S. Aoki, D. Kagata, M. Shiro, K. Takeda, and E. Kimura, “Metal chelation-controlled twisted intramolecular charge transfer and its application to fluorescent sensing of metal ions and anions,” J. Am. Chem. Soc. 126(41), 13377–13390 (2004).
[Crossref] [PubMed]

Kuke, S.

S. Ast, S. Kuke, P. J. Rutledge, and M. H. Todd, “Using click chemistry to Tune the Properties and the Fluorescence Response Mechanism of Structurally Similar Probes for Metal Ions,” Eur. J. Inorg. Chem. 2015(1), 58–66 (2015).
[Crossref]

Lambert, C. J.

C. J. Lambert, “Basic concepts of quantum interference and electron transport in single-molecule electronics,” Chem. Soc. Rev. 44(4), 875–888 (2015).
[Crossref] [PubMed]

Lippert, E.

E. Lippert, W. Luder, F. Moll, H. Naggele, H. Boos, H. Prigge, and I. Siebold-Blankenstein, “Transformation of electron excitation energy,” Angew. Chem. 73, 695–706 (1961).
[Crossref]

Luder, W.

E. Lippert, W. Luder, F. Moll, H. Naggele, H. Boos, H. Prigge, and I. Siebold-Blankenstein, “Transformation of electron excitation energy,” Angew. Chem. 73, 695–706 (1961).
[Crossref]

Moll, F.

E. Lippert, W. Luder, F. Moll, H. Naggele, H. Boos, H. Prigge, and I. Siebold-Blankenstein, “Transformation of electron excitation energy,” Angew. Chem. 73, 695–706 (1961).
[Crossref]

Naggele, H.

E. Lippert, W. Luder, F. Moll, H. Naggele, H. Boos, H. Prigge, and I. Siebold-Blankenstein, “Transformation of electron excitation energy,” Angew. Chem. 73, 695–706 (1961).
[Crossref]

Placido, T.

L. De Sio, T. Placido, R. Comparelli, M. L. Curri, M. Striccoli, N. Tabiryan, and T. J. Bunning, “Next-generation thermo-plasmonic technologies and plasmonic nanoparticles in optoelectronics,” Progress in Quant. Electron. 41, 23–70 (2015).

Prigge, H.

E. Lippert, W. Luder, F. Moll, H. Naggele, H. Boos, H. Prigge, and I. Siebold-Blankenstein, “Transformation of electron excitation energy,” Angew. Chem. 73, 695–706 (1961).
[Crossref]

Rettig, W.

W. Rettig, “Charge separation in excited states of decoupled systems-TICT compounds and implications regarding the development of new laser dyes and the primary process,” Angew. Chem. Int. Ed. Engl. 25(11), 971–988 (1986).
[Crossref]

Rotkiewicz, K.

K. Rotkiewicz, K. H. Grellman, and Z. R. Grabowski, “Reinterpretation of the anomalous fluorescense of pn, n-dimethylamino-benzonitrile,” Chem. Phys. Lett. 19(3), 315–318 (1973).
[Crossref]

Rutledge, P. J.

S. Ast, S. Kuke, P. J. Rutledge, and M. H. Todd, “Using click chemistry to Tune the Properties and the Fluorescence Response Mechanism of Structurally Similar Probes for Metal Ions,” Eur. J. Inorg. Chem. 2015(1), 58–66 (2015).
[Crossref]

M. Arafat Hossain, J. Canning, S. Ast, K. Cook, P. J. Rutledge, and A. Jamalipour, “Combined “dual” absorption and fluorescence smartphone spectrometers,” Opt. Lett. 40(8), 1737–1740 (2015).
[Crossref] [PubMed]

S. Ast, P. J. Rutledge, and M. H. Todd, “Reversing the Triazole Topology in a Cyclam‐Triazole‐Dye Ligand Gives a 10‐Fold Brighter Signal Response to Zn2+ in Aqueous Solution,” Eur. J. Inorg. Chem. 2012(34), 5611–5615 (2012).
[Crossref]

Salzmann, I.

I. Salzmann and G. Heimel, “Towards a comprehensive understanding of molecular doping organic semiconductors,” J. Electron Spectrosc. Relat. Phenom.In press., doi:.
[Crossref]

Sareen, D.

D. Sareen, P. Kaur, and K. Singh, “Strategies in detection of metal ions using dyes,” Coord. Chem. Rev. 265, 125–154 (2014).
[Crossref]

Shiro, M.

S. Aoki, D. Kagata, M. Shiro, K. Takeda, and E. Kimura, “Metal chelation-controlled twisted intramolecular charge transfer and its application to fluorescent sensing of metal ions and anions,” J. Am. Chem. Soc. 126(41), 13377–13390 (2004).
[Crossref] [PubMed]

Siebold-Blankenstein, I.

E. Lippert, W. Luder, F. Moll, H. Naggele, H. Boos, H. Prigge, and I. Siebold-Blankenstein, “Transformation of electron excitation energy,” Angew. Chem. 73, 695–706 (1961).
[Crossref]

Singh, K.

D. Sareen, P. Kaur, and K. Singh, “Strategies in detection of metal ions using dyes,” Coord. Chem. Rev. 265, 125–154 (2014).
[Crossref]

Steuerman, D. W.

A. H. Flood, J. F. Stoddart, D. W. Steuerman, and J. R. Heath, “Chemistry. Whence molecular electronics?” Science 306(5704), 2055–2056 (2004).
[Crossref] [PubMed]

Stoddart, J. F.

A. H. Flood, J. F. Stoddart, D. W. Steuerman, and J. R. Heath, “Chemistry. Whence molecular electronics?” Science 306(5704), 2055–2056 (2004).
[Crossref] [PubMed]

Striccoli, M.

L. De Sio, T. Placido, R. Comparelli, M. L. Curri, M. Striccoli, N. Tabiryan, and T. J. Bunning, “Next-generation thermo-plasmonic technologies and plasmonic nanoparticles in optoelectronics,” Progress in Quant. Electron. 41, 23–70 (2015).

Tabiryan, N.

L. De Sio, T. Placido, R. Comparelli, M. L. Curri, M. Striccoli, N. Tabiryan, and T. J. Bunning, “Next-generation thermo-plasmonic technologies and plasmonic nanoparticles in optoelectronics,” Progress in Quant. Electron. 41, 23–70 (2015).

Takeda, K.

S. Aoki, D. Kagata, M. Shiro, K. Takeda, and E. Kimura, “Metal chelation-controlled twisted intramolecular charge transfer and its application to fluorescent sensing of metal ions and anions,” J. Am. Chem. Soc. 126(41), 13377–13390 (2004).
[Crossref] [PubMed]

Todd, M. H.

S. Ast, S. Kuke, P. J. Rutledge, and M. H. Todd, “Using click chemistry to Tune the Properties and the Fluorescence Response Mechanism of Structurally Similar Probes for Metal Ions,” Eur. J. Inorg. Chem. 2015(1), 58–66 (2015).
[Crossref]

S. Ast, P. J. Rutledge, and M. H. Todd, “Reversing the Triazole Topology in a Cyclam‐Triazole‐Dye Ligand Gives a 10‐Fold Brighter Signal Response to Zn2+ in Aqueous Solution,” Eur. J. Inorg. Chem. 2012(34), 5611–5615 (2012).
[Crossref]

Tour, J. M.

J. M. Tour, “Molecular electronics. Synthesis and testing of components,” Acc. Chem. Res. 33(11), 791–804 (2000).
[Crossref] [PubMed]

Acc. Chem. Res. (1)

J. M. Tour, “Molecular electronics. Synthesis and testing of components,” Acc. Chem. Res. 33(11), 791–804 (2000).
[Crossref] [PubMed]

Angew. Chem. (1)

E. Lippert, W. Luder, F. Moll, H. Naggele, H. Boos, H. Prigge, and I. Siebold-Blankenstein, “Transformation of electron excitation energy,” Angew. Chem. 73, 695–706 (1961).
[Crossref]

Angew. Chem. Int. Ed. Engl. (1)

W. Rettig, “Charge separation in excited states of decoupled systems-TICT compounds and implications regarding the development of new laser dyes and the primary process,” Angew. Chem. Int. Ed. Engl. 25(11), 971–988 (1986).
[Crossref]

Chem. Phys. Lett. (1)

K. Rotkiewicz, K. H. Grellman, and Z. R. Grabowski, “Reinterpretation of the anomalous fluorescense of pn, n-dimethylamino-benzonitrile,” Chem. Phys. Lett. 19(3), 315–318 (1973).
[Crossref]

Chem. Soc. Rev. (1)

C. J. Lambert, “Basic concepts of quantum interference and electron transport in single-molecule electronics,” Chem. Soc. Rev. 44(4), 875–888 (2015).
[Crossref] [PubMed]

Coord. Chem. Rev. (1)

D. Sareen, P. Kaur, and K. Singh, “Strategies in detection of metal ions using dyes,” Coord. Chem. Rev. 265, 125–154 (2014).
[Crossref]

Eur. J. Inorg. Chem. (2)

S. Ast, P. J. Rutledge, and M. H. Todd, “Reversing the Triazole Topology in a Cyclam‐Triazole‐Dye Ligand Gives a 10‐Fold Brighter Signal Response to Zn2+ in Aqueous Solution,” Eur. J. Inorg. Chem. 2012(34), 5611–5615 (2012).
[Crossref]

S. Ast, S. Kuke, P. J. Rutledge, and M. H. Todd, “Using click chemistry to Tune the Properties and the Fluorescence Response Mechanism of Structurally Similar Probes for Metal Ions,” Eur. J. Inorg. Chem. 2015(1), 58–66 (2015).
[Crossref]

J. Am. Chem. Soc. (1)

S. Aoki, D. Kagata, M. Shiro, K. Takeda, and E. Kimura, “Metal chelation-controlled twisted intramolecular charge transfer and its application to fluorescent sensing of metal ions and anions,” J. Am. Chem. Soc. 126(41), 13377–13390 (2004).
[Crossref] [PubMed]

Nature (1)

H. B. Akkerman, P. W. M. Blom, D. M. de Leeuw, and B. de Boer, “Towards molecular electronics with large-area molecular junctions,” Nature 441(7089), 69–72 (2006).
[Crossref] [PubMed]

Opt. Lett. (1)

Progress in Quant. Electron. (1)

L. De Sio, T. Placido, R. Comparelli, M. L. Curri, M. Striccoli, N. Tabiryan, and T. J. Bunning, “Next-generation thermo-plasmonic technologies and plasmonic nanoparticles in optoelectronics,” Progress in Quant. Electron. 41, 23–70 (2015).

Science (1)

A. H. Flood, J. F. Stoddart, D. W. Steuerman, and J. R. Heath, “Chemistry. Whence molecular electronics?” Science 306(5704), 2055–2056 (2004).
[Crossref] [PubMed]

Other (1)

I. Salzmann and G. Heimel, “Towards a comprehensive understanding of molecular doping organic semiconductors,” J. Electron Spectrosc. Relat. Phenom.In press., doi:.
[Crossref]

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Figures (6)

Fig. 1
Fig. 1

Blue emission (λex ~370 nm, λem ~458 nm) from 1 before and after Zn2+ incorporation in HEPES buffer (pH ~8). The structures are likely solvated. Smartphone spectrometer images @λem ~ 458 nm are shown below (from [14]).

Fig. 2
Fig. 2

Normalised emission spectra (λex ~370 nm) of (a) 1 in HEPES buffer, and (b) with added Zn2+ as [1:Zn]2+. Peak fitting (χ2 = 0.0025) reveals two bands in the blue that accounts for the asymmetric spectra, corresponding to the conjugated ligand emission at shorter wavelengths and the TICT-related emission.

Fig. 3
Fig. 3

Normalised emission spectra (λex ~370 nm) of (a) 1 in HEPES buffer, and (b) with added Cu2+ as [1:Cu]2+. Peak fitting (χ2 = 0.084) reveals two bands corresponding to the conjugated ligand and red-shifted TICT emissions.

Fig. 4
Fig. 4

Evolution of florescence intensity, I, at λem = 458 nm (λex = 370 nm) versus time, t, for different temperatures (T = 15 to 55 °C) for Cu2+ and Zn2+ complexes of 1. The free ligand range measurements at 15 °C and 55 °C were constant and flat over this time period, defining the border of the shaded region in which the ligand emission is affected.

Fig. 5
Fig. 5

ChemBioDraw structures of 1 (a) without and (b) with Zn2+ shown with yellow arrow. As a result of electrostatic interactions, the cyclam group is more twisted and bent out of plane with the naphthalimide group.

Fig. 6
Fig. 6

A molecular optical diode: charge transport through the bridging triazole N determines hole generation and recombination. On the right are allowed transitions for (a) no complexation where emission is poor due to PET to an exciplex-like state; (b) Zn2+ complex leading to a higher energy for emission when the bias is preferentially through the triazole N instead of PET; (c) Cu2+ complex leading to higher energy of emission but with induced bias in the wrong direction, so emissions are quenched (dashed lines) as PET charge transfer is consequentially increased.

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