Coumarin dyes

from Wikipedia, the free encyclopedia

Coumarin dyes (Engl. Coumarin dyes ) are a class of fluorescent dyes originally for use in dye lasers as well as have been developed polarity- , pH and viscosity sensitive and find fluorophores as a fluorescent label or marker used. They are derivatives of coumarin , a naturally occurring secondary plant substance .

Structure and properties

  • Numbering of the heterocycle coumarin.

  • Coumarin 120 ( 7-Amino-4-methylcoumarin )

  • Coumarin 1 ( Coumarin 47 )

  • Coumarin 102

  • Coumarin 307

  • Coumarin 152

  • Coumarin 153

  • Coumarin 6

The most commonly used coumarin dyes are the 7-aminocoumarins . These have an amino group at the C-7 position, the carbon atoms of the six-membered double-ring heterocycle being counted on the oxygen heteroatom of the 2-pyrone (see right graphic above).

By an intramolecular charge transfer (engl. Intramolecular charge-transfer , ICT) from the as electron donor (engl. Electron donating group functioning, EDG) amino group to the carbonyl group of the 2-pyrone or an additionally present electron acceptor (engl. Electron Withdrawing group , EWG ) at the C-3 or C-4 position, these coumarin dyes receive their specific photophysical properties. The 7-aminocoumarins can in principle be described by two mesomeric states: a non-polar state, which predominates in the S 0 ground state and has a low electrical dipole moment , and a polar state in which a positive charge is localized on the nitrogen atom and a negative charge on the 2-pyrone is. This state has an increased dipole moment and is predominantly predominant in the excited state S 1 . In the following, the two possible mesomeric states are shown using the example of coumarin 120:

Coumarin120 mesomeric.png

The range of light absorption of coumarin dyes ( 7-aminocoumarins ) extends from the near UV (UV-A) to the blue spectral range , with the emission of fluorescence in the blue to green-yellow spectral range. The photophysical properties strongly depend on the solvent used . So z. B. the mesomeric state with the high dipole moment is more stabilized by polar solvents, which typically causes a red shift in the absorption of the coumarin dyes. Furthermore, a realignment of polar solvent molecules is caused by optical excitation of the S 1 level, which lowers the energy of the excited state and results in a red shift of the emission. This is stronger than the redshift of the absorption and thus increases the Stokes shift .

The coumarins used as laser dyes have a very high quantum yield in non-polar solvents, which typically decreases with increasing polarity of the solvent. In the case of coumarin dyes with rigid side chains on the nitrogen atom, the decrease in the quantum yield is not so pronounced, since the freely rotatable side chains can favor competing non-radiative transitions into the S 0 ground state. Furthermore, the probability of a spin flip (from the singlet state to the triplet state ) is very low, so that coumarins are rarely in the long-lived triplet state in which they do not fluoresce.

Overview of frequently used coumarin dyes

The table below shows a selection of frequently used coumarin dyes. The approximate emission range for various solvents as well as the absorption and emission maximum for ethanol are given (in nanometers) .

Name ( alias ) Max. in EtOH Max. in EtOH Emission range
Coumarin 120 354 435 420-470
Coumarin 1 (47; 460) 373 450 440-490
Coumarin 102 (480) 389 465 450-510
Coumarin 307 395 490 480-550
Coumarin 152 397 510 490-570
Coumarin 153 (540A) 423 530 520-590
Coumarin 6 458 505 500-560

The commercially available fluorescent dyes or labels Alexa Fluor 350 and 430 (Molecular Probes / Invitrogen Corp.), as well as ATTO 390 and 425 ( ATTO-TEC GmbH , Siegen) are also coumarin derivatives and can be found among others. a. often used in fluorescence microscopy .

See also

literature

  • Ulrich Brackmann: Lambdachrome: Laser Dyes . 3. Edition. Lamda Physik AG, Göttingen 2000 ( PDF ).
  • Eunha Kim, Seung Bum Park: Discovery of New Fluorescent Dyes: Targeted Synthesis or Combinatorial Approach? In: Alexander P. Demchenko (Ed.): Advanced Fluorescence Reporters in Chemistry and Biology. Volume I: Fundamentals and Molecular Design (=  Springer Series on Fluorescence ). Springer, Berlin / Heidelberg 2010, ISBN 978-3-642-04700-8 , pp. 150 ff .
  • M. Sauer, J. Hofkens, J. Enderlein: Handbook of Fluorescence Spectroscopy and Imaging: From Single Molecules to Ensembles: From Ensemble to Single Molecules . Wiley-VCH Verlag, Weinheim 2011, ISBN 978-3-527-31669-4 , pp. 39 ff .

Individual evidence

  1. ↑ Eunha Kim, Seung Bum Park: Discovery of New Fluorescent Dyes: Targeted Synthesis or Combinatorial Approach? In: Alexander P. Demchenko (Ed.): Advanced Fluorescence Reporters in Chemistry and Biology. Volume I: Fundamentals and Molecular Design (=  Springer Series on Fluorescence ). Springer, Berlin / Heidelberg 2010, ISBN 978-3-642-04700-8 , pp. 150 ff .
  2. ↑ a b c M. Sauer, J. Hofkens, J. Enderlein: Handbook of Fluorescence Spectroscopy and Imaging: From Single Molecules to Ensembles: From Ensemble to Single Molecules . Wiley-VCH Verlag, Weinheim 2011, ISBN 978-3-527-31669-4 , pp. 39 ff . ( limited preview in Google Book search).
  3. ^ Brian D. Wagner: The Use of Coumarins as Environmentally-Sensitive Fluorescent Probes of Heterogeneous Inclusion Systems. In: Molecules . Vol. 14, 2009, pp. 210-237, doi: 10.1201 / b13129-16 . (PDF)
  4. ↑ Sanjukta Nad, Manoj Kumbhakar, Haridas Pal: Photophysical Properties of Coumarin-152 and Coumarin-481 Dyes: Unusual Behavior in Nonpolar and in Higher Polarity Solvents. In: J. Phys. Chem. A . Vol. 107 (24), 2003, pp. 4808-4816, doi: 10.1021 / jp021543t . (PDF)
  5. ↑ GA Reynolds, KH Drexhage: New coumarin dyes with rigidized structure for flashlamp-pumped dye lasers. In: Optics Communications . Vol. 13, No. 3, 1975, pp. 222-225, doi: 10.1016 / 0030-4018 (75) 90085-1 .
  6. ↑ Ulrich Brack man: Lambdachrome®: Laser Dyes . 3. Edition. Lamda Physik AG, Göttingen 2000 ( PDF ).