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As fluorophores play the central role in fluorescence spectroscopy and imaging we will start with an investigation of their manifold interactions with light. A fluorophore is a component that causes a molecule to absorb energy of a specific wavelength and then re-remit energy at a different but equally specific wavelength. The amount and wavelength of the emitted energy depend on both the fluorophore and the chemical environment of the fluorophore. Fluorophores are also denoted as chromophores, historically speaking the part or moiety of a molecule responsible for its color. In addition, the denotation chromophore implies that the molecule absorbs light while fluorophore means that the molecule, likewise,emits light. The umbrella term used in light emission is luminescence, whereas fluorescence denotes allowed transitions with a lifetime in the nanosecond range from higher to lower excited singlet states of molecules.In the following we will try to understand why some compounds are colored and others are not. Therefore, we will take a closer look at the relationship of conjugation to color with fluorescence emission, and investigate the absorption of light at different wavelengths in and near the visible part of the spectrum of various compounds. For example, organic compounds (i.e., hydrocarbons and derivatives) without double or triple bonds absorb light at wavelengths below 160 nm, corresponding to a photon energy of >180 kcal mol À1 (1 cal ¼ 4.184 J), or >7.8 eV (Figure 1.1), that is, significantly higher than the dissociation energy of common carbon-to-carbon single bonds.Below a wavelength of 200 nm the energy of a single photon is sufficient to ionize molecules. Therefore, photochemical decomposition is most likely to occur when unsaturated compounds, where all bonds are formed by s-electrons, are irradiated with photon energies >6.2 eV. Double and triple bonds also use p-electrons in addition to a s-bond for bonding. In contrast to s-electrons, which are characterized by the rotational symmetry of their wavefunction with respect to the bond direction, p-electrons are characterized by a wavefunction having a node at the nucleus and rotational symmetry along a line through the nucleus. p-bonds
As fluorophores play the central role in fluorescence spectroscopy and imaging we will start with an investigation of their manifold interactions with light. A fluorophore is a component that causes a molecule to absorb energy of a specific wavelength and then re-remit energy at a different but equally specific wavelength. The amount and wavelength of the emitted energy depend on both the fluorophore and the chemical environment of the fluorophore. Fluorophores are also denoted as chromophores, historically speaking the part or moiety of a molecule responsible for its color. In addition, the denotation chromophore implies that the molecule absorbs light while fluorophore means that the molecule, likewise,emits light. The umbrella term used in light emission is luminescence, whereas fluorescence denotes allowed transitions with a lifetime in the nanosecond range from higher to lower excited singlet states of molecules.In the following we will try to understand why some compounds are colored and others are not. Therefore, we will take a closer look at the relationship of conjugation to color with fluorescence emission, and investigate the absorption of light at different wavelengths in and near the visible part of the spectrum of various compounds. For example, organic compounds (i.e., hydrocarbons and derivatives) without double or triple bonds absorb light at wavelengths below 160 nm, corresponding to a photon energy of >180 kcal mol À1 (1 cal ¼ 4.184 J), or >7.8 eV (Figure 1.1), that is, significantly higher than the dissociation energy of common carbon-to-carbon single bonds.Below a wavelength of 200 nm the energy of a single photon is sufficient to ionize molecules. Therefore, photochemical decomposition is most likely to occur when unsaturated compounds, where all bonds are formed by s-electrons, are irradiated with photon energies >6.2 eV. Double and triple bonds also use p-electrons in addition to a s-bond for bonding. In contrast to s-electrons, which are characterized by the rotational symmetry of their wavefunction with respect to the bond direction, p-electrons are characterized by a wavefunction having a node at the nucleus and rotational symmetry along a line through the nucleus. p-bonds
Systeme uus rnonomolekularen Schichten kiinnen Funktionseinheiten bilden, welche Eigenschaften entfalten, die den Einzelschichten fehlen. Sofindet z. B. bei UVBestrahlung ein Energieubergang con einer Sensibilisutor-(S-)Schicht auf eine Acceptor-(A-jSchicht statt, der sich durch Fluoreszenz con
Unerwartetes Aufleuchten: Eine leichte Rotationsverdrillung und Versteifung von Merocyanin‐Farbstoffen in einem π‐π‐gestapelten Dimer‐Aggregat resultierte in einer unerwarteten Steigerung von Fluoreszenzintensität und ‐lebensdauer (siehe Diagramm). Diese Beobachtung widerspricht der allgemeinen Annahme, dass die Fluoreszenz von H‐Aggregaten stark gelöscht wird, kann aber durch die Exzitonentheorie erklärt werden.
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