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Related Concept Videos

Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Aryldiazonium Salts to Azo Dyes: Diazo Coupling01:11

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The reaction of weakly electrophilic aryldiazonium (also called arenediazonium) salts with highly activated aromatic compounds leads to the formation of products with an —N=N— link, called an azo linkage. This reaction, presented in Figure 1, is known as diazo coupling and occurs without the loss of the nitrogen atoms of the aryldiazonium salt. Highly activated aromatic compounds such as phenols or arylamines favor the diazo coupling reaction. The coupling generally occurs at the para position.
¹³C NMR: ¹H–¹³C Decoupling01:04

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The probability of having two carbon-13 atoms next to each other is negligible because of the low natural abundance of carbon-13. Consequently, peak splitting due to carbon-carbon spin-spin coupling is not observed in spectra. However, protons up to three sigma bonds away split the carbon signal according to the n+1 rule, resulting in complicated spectra.
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Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

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Double Resonance Techniques: Overview01:12

Double Resonance Techniques: Overview

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Patterning via Optical Saturable Transitions - Fabrication and Characterization
08:19

Patterning via Optical Saturable Transitions - Fabrication and Characterization

Published on: December 11, 2014

Carbocyanine dyes as efficient reversible single-molecule optical switch.

Mike Heilemann1, Emmanuel Margeat, Robert Kasper

  • 1Applied Laserphysics & Laserspectroscopy, Physics Faculty, University of Bielefeld, Universitätsstrasse 25, 33615 Bielefeld, Germany.

Journal of the American Chemical Society
|March 18, 2005
PubMed
Summary

Commercially available Cy5 dyes act as reversible optical switches. Their fluorescence can be restored after photobleaching, enabling applications in optical data storage and impacting biological studies.

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Area of Science:

  • Photochemistry
  • Molecular Biophysics
  • Materials Science

Background:

  • Carbocyanine dyes, like Cy5, are widely used fluorescent labels.
  • Photobleaching limits their long-term stability and application scope.
  • Understanding reversible switching is key for advanced optical applications.

Purpose of the Study:

  • To investigate the reversible optical switching capabilities of unmodified carbocyanine dyes.
  • To explore the conditions required for restoring fluorescence after photobleaching.
  • To assess the potential of these dyes for optical data storage and their limitations in biological assays.

Main Methods:

  • Ensemble photobleaching and recovery experiments in aqueous solutions.
  • Single-molecule fluorescence spectroscopy of immobilized Cy5 molecules.
  • Alternating excitation at 633 nm and 488 nm for optical switching.
  • Fluorescence resonance energy transfer (FRET) measurements on labeled oligonucleotides.

Main Results:

  • Cy5 dyes function as efficient reversible single-molecule optical switches.
  • Fluorescence restoration is achievable at room temperature via irradiation at shorter wavelengths (337, 488, or 532 nm).
  • Restoration efficacy depends on oxygen removal and triplet quenchers (e.g., beta-mercaptoethylamine).
  • Individual Cy5 molecules switched over 100 times with >90% reliability in milliseconds.
  • Carbocyanine dye switching behavior limits their use as FRET acceptors in biological studies.

Conclusions:

  • Unmodified carbocyanine dyes offer a simple, efficient, and reversible optical switching mechanism.
  • These dyes show promise for ultrahigh-density optical data storage applications.
  • The light-driven switching behavior presents fundamental limitations for using them as energy transfer acceptors in biological research.