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Suppression of Kasha's rule as a mechanism for fluorescent molecular rotors and aggregation-induced emission

Abstract

Although there are some proposed explanations for aggregation-induced emission, a phenomenon with applications that range from biosensors to organic light-emitting diodes, current understanding of the quantum-mechanical origin of this photophysical behaviour is limited. To address this issue, we assessed the emission properties of a series of BF2–hydrazone-based dyes as a function of solvent viscosity. These molecules turned out to be highly efficient fluorescent molecular rotors. This property, in addition to them being aggregation-induced emission luminogens, enabled us to probe deeper into their emission mechanism. Time-dependent density functional theory calculations and experimental results showed that the emission is not from the S1 state, as predicted from Kasha's rule, but from a higher energy (>S1) state. Furthermore, we found that suppression of internal conversion to the dark S1 state by restricting the rotor rotation enhances fluorescence, which leads to the proposal that suppression of Kasha's rule is the photophysical mechanism responsible for emission in both viscous solution and the solid state.

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Figure 1: The absorption (dashed line) and fluorescence (solid lines) spectra of compound 4 in mixtures of Gly and EG of increased solvent viscosity.
Figure 2: Ground (blue diamonds) and excited (shaded red diamonds) PBE TDDFT state energies of 1 as a function of rotor angle.
Figure 3: Excitation-dependent corrected emission spectra of compound 1 in dichloromethane.

References

  1. Haidekker, M. A. & Theodorakis, E. A. Environment-sensitive behavior of fluorescent molecular rotors. J. Biol. Eng. 4, 11–24 (2010).

    Article  Google Scholar 

  2. Kuimova, M. K. Mapping viscosity in cells using molecular rotors. Phys. Chem. Chem. Phys. 14, 12671–12686 (2012).

    CAS  Article  Google Scholar 

  3. Srivatsan, S. G., Greco, N. J. & Tor, Y. A highly emissive fluorescent nucleoside that signals the activity of toxic ribosome-inactivating proteins. Angew. Chem. Int. Ed. 47, 6661–6665 (2008).

    CAS  Article  Google Scholar 

  4. Kuimova, M. K. et al. Imaging intracellular viscosity of a single cell during photoinduced cell death. Nat. Chem. 1, 69–73 (2009).

    CAS  Article  Google Scholar 

  5. Cao, K. et al. Aminonaphthalene 2-cyanoacrylate (ANCA) probes fluorescently discriminate between amyloid-β and prion plaques in brain. J. Am. Chem. Soc. 134, 17338–17341 (2012).

    CAS  Article  Google Scholar 

  6. Wang, L., Xiao, Y., Tian, W. & Deng, L. Activatable rotor for quantifying lysosomal viscosity in living cells. J. Am. Chem. Soc. 135, 2903–2906 (2013).

    CAS  Article  Google Scholar 

  7. Cui, M. C. et al. Smart near-infrared fluorescence probes with donor–acceptor structure for in vivo detection of β-amyloid deposits. J. Am. Chem. Soc. 136, 3388–3394 (2014).

    CAS  Article  Google Scholar 

  8. Levitt, J. A. et al. Membrane-bound molecular rotors measure viscosity in live cells via fluorescence lifetime imaging. J. Phys. Chem. C 113, 11634–11642 (2009).

    CAS  Article  Google Scholar 

  9. Hosny, N. A. et al. Mapping microbubble viscosity using fluorescence lifetime imaging of molecular rotors. Proc. Natl Acad. Sci. USA 110, 9225–9230 (2013).

    CAS  Article  Google Scholar 

  10. Shiraishi, Y., Inoue, T. & Hirai, T. Local viscosity analysis of triblock copolymer micelle with cyanine dyes as a fluorescent probe. Langmuir 26, 17505–17512 (2010).

    CAS  Article  Google Scholar 

  11. Vaccaro, G. et al. Direct monitoring of self-assembly of copolymeric micelles by a luminescent molecular rotor. Chem. Commun. 49, 8474–8476 (2013).

    CAS  Article  Google Scholar 

  12. Feng, J. et al. A triarylboron-based fluorescent thermometer: sensitive over a wide temperature range. Angew. Chem. Int. Ed. 50, 8072–8076 (2011).

    CAS  Article  Google Scholar 

  13. Peng, X. J. et al. Fluorescence ratiometry and fluorescence lifetime imaging: using a single molecular sensor for dual mode imaging of cellular viscosity. J. Am. Chem. Soc. 133, 6626–6635 (2011).

    CAS  Article  Google Scholar 

  14. Gatzogiannis, E. et al. Mapping protein-specific micro-environments in live cells by fluorescence lifetime imaging of a hybrid genetic-chemical molecular rotor tag. Chem. Commun. 48, 8694–8696 (2012).

    CAS  Article  Google Scholar 

  15. Haidekker, M. A., Brady, T. P., Lichlyter, D. & Theodorakis, E. A. Effects of solvent polarity and solvent viscosity on the fluorescent properties of molecular rotors and related probes. Bioorg. Chem. 33, 415–425 (2005).

    CAS  Article  Google Scholar 

  16. Bochkov, A. Y., Akchurin, I. O., Dyachenko, O. A. & Traven, V. F. NIR-fluorescent coumarin-fused BODIPY dyes with large Stokes shifts. Chem. Commun. 49, 11653–11655 (2013).

    CAS  Article  Google Scholar 

  17. Cosgrave, L., Devocelle, M., Forster, R. J. & Keyes, T. E. Multimodal cell imaging by ruthenium polypyridyl labelled cell penetrating peptides. Chem. Commun. 46, 103–105 (2010).

    CAS  Article  Google Scholar 

  18. Zhou, Y., Xiao, Y., Chi, S. M. & Qian, X. H. Isomeric boron–fluorine complexes with donor–acceptor architecture: strong solid/liquid fluorescence and large Stokes shift. Org. Lett. 10, 633–636 (2008).

    CAS  Article  Google Scholar 

  19. Yang, Y., Su, X., Carroll, C. N. & Aprahamian, I. Aggregation-induced emission in BF2-hydrazone (BODIHY) complexes. Chem. Sci. 3, 610–613 (2012).

    CAS  Article  Google Scholar 

  20. Yang, Y. Hydrazone-Based Macrocycles, Fluorophores and Light-Activated Switches PhD Thesis, Dartmouth College (2014).

    Google Scholar 

  21. Su, X. & Aprahamian, I. Hydrazone-based switches, metallo-assemblies and sensors. Chem. Soc. Rev. 43, 1963–1981 (2014).

    CAS  Article  Google Scholar 

  22. Tatum, L. A., Su, X. & Aprahamian, I. Simple hydrazone building blocks for complicated functional materials. Acc. Chem. Res. 47, 2141–2149 (2014).

    CAS  Article  Google Scholar 

  23. Hong, Y. N., Lam, J. W. Y. & Tang, B. Z. Aggregation-induced emission. Chem. Soc. Rev. 40, 5361–5388 (2011).

    CAS  Article  Google Scholar 

  24. Leung, N. L. C. et al. Restriction of intramolecular motions: the general mechanism behind aggregation-induced emission. Chem. Eur. J. 20, 15349–15353 (2014).

    CAS  Article  Google Scholar 

  25. Mei, J., Leung, N. L. C., Kwok, R. T. K., Lam, J. W. Y. & Tang, B. Z. Aggregation-induced emission: together we shine, united we soar! Chem. Rev. 115, 11718–11940 (2015).

    CAS  Article  Google Scholar 

  26. Born, M. & Oppenheimer, R. Zur Quantentheorie der Molekeln [in German]. Ann. Phys. 389, 457–484 (1927).

    Article  Google Scholar 

  27. Kee, H. L. et al. Structural control of the photodynamics of boron–dipyrrin complexes. J. Phys. Chem. B 109, 20433–20443 (2005).

    CAS  Article  Google Scholar 

  28. Zhou, F. K. et al. Molecular rotors as fluorescent viscosity sensors: molecular design, polarity sensitivity, dipole moments changes, screening solvents, and deactivation channel of the excited states. Eur. J. Org. Chem. 4773–4787 (2011).

  29. Shao, J. Y. et al. Thiophene-inserted aryl-dicyanovinyl compounds: the second generation of fluorescent molecular rotors with significantly redshifted emission and large Stokes shift. Eur. J. Org. Chem. 6100–6109 (2011).

    CAS  Article  Google Scholar 

  30. Peng, Q., Niu, Y. L., Deng, C. M. & Shuai, Z. G. Vibration correlation function formalism of radiative and non-radiative rates for complex molecules. Chem. Phys. 370, 215–222 (2010).

    CAS  Article  Google Scholar 

  31. Shuai, Z. G. & Peng, Q. Excited states structure and processes: understanding organic light-emitting diodes at the molecular level. Phys. Rep. 537, 123–156 (2014).

    CAS  Article  Google Scholar 

  32. Kasha, M. Characterization of electronic transitions in complex molecules. Disc. Faraday Soc. 14–19 (1950).

    Article  Google Scholar 

  33. Munkholm, C., Parkinson, D. R. & Walt, D. R. Intramolecular fluorescence self-quenching of fluoresceinamine. J. Am. Chem. Soc. 112, 2608–2612 (1990).

    CAS  Article  Google Scholar 

  34. Ueno, T., Urano, Y., Kojima, H. & Nagano, T. Mechanism-based molecular design of highly selective fluorescence probes for nitrative stress. J. Am. Chem. Soc. 128, 10640–10641 (2006).

    CAS  Article  Google Scholar 

  35. Jacquemin, D., Mennucci, B. & Adamo, C. Excited-state calculations with TD-DFT: from benchmarks to simulations in complex environments. Phys. Chem. Chem. Phys. 13, 16987–16998 (2011).

    CAS  Article  Google Scholar 

  36. Englman, R. The energy gap law for radiationless transitions in large molecules. Mol. Phys. 18, 145–164 (1970).

    CAS  Article  Google Scholar 

  37. Itoh, T. Fluorescence and phosphorescence from higher excited states of organic molecules. Chem. Rev. 112, 4541–4568 (2012).

    CAS  Article  Google Scholar 

  38. Mei, J. et al. Aggregation-induced emission: the whole is more brilliant than the parts. Adv. Mater. 26, 5429–5479 (2014).

    CAS  Article  Google Scholar 

Download references

Acknowledgements

I.A. and M.D.L. acknowledge the support of the National Science Foundation (DMR-1506170 and DMR-1506248, respectively). A.W. acknowledges the support of the ACS Project SEED program.

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Authors

Contributions

All the experiments were conducted by H.Q., M.E.C., E.H.H. and A.W. with input from I.A. and M.D.L. All the computational work was conducted by M.E.C. and E.H.H. with the supervision of M.D.L. The manuscript was written jointly by H.Q., I.A., M.E.C. and M.D.L.

Corresponding authors

Correspondence to Matthew D. Liptak or Ivan Aprahamian.

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The authors declare no competing financial interests.

Supplementary information

Supplementary information

Supplementary information (PDF 3974 kb)

Supplementary information

Crystallographic data for compound 2. (CIF 242 kb)

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Structure factors file for compound 2. (FCF 132 kb)

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Qian, H., Cousins, M., Horak, E. et al. Suppression of Kasha's rule as a mechanism for fluorescent molecular rotors and aggregation-induced emission. Nature Chem 9, 83–87 (2017). https://doi.org/10.1038/nchem.2612

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