Would the maximum peak for excitation and emission spectra using a fluorolog be

Question

Would the maximum peak for excitation and emission spectra using a fluorolog be at the same wavelength. For example, if your highest intensity peak is 468nm for excitation, is it possible for your maximum intensity to be 350 in the corresponding emission spectra? Shouldn't the emission peak be at a longer wavelength? Would the maximum peak for excitation and emission spectra using a fluorolog be at the same wavelength. For example, if your highest intensity peak is 468nm for excitation, is it possible for your maximum intensity to be 350 in the corresponding emission spectra? Shouldn't the emission peak be at a longer wavelength?

Explanation / Answer

In most cases,the emission occurs at a longer wavelength than are required for excitation.This difference,the Stokes shift is due to a variety of factors .some of these factors are intrinsic due to the fluorophore and some are due to interactions of the fluorophore with its environment.

Photon absorption occurs on a very short time scale (~10–15 seconds). Several processes then may occur. If the molecule is excited beyond the first excited electronic state (e.g., the S2 state), it will usually rapidly lose energy via internal conversion, to reach the lowest energy singlet excited state, S1, in a process that takes ~10–12 seconds. In most cases, the excited state will vibrationally relax to reach the lowest energy state within the excited state.

If the fluorophore has a larger dipole moment in the excited state (which is usually the case, especially for polar fluorophores), the solvent will rearrange to stabilize the greater charge separation. the fluorophore in the ground state (µG) absorbs a photon to transition to an excited state (µE). The surrounding solvent molecules do not move during the absorption process. The solvent molecules can then rearrange to adapt to the altered properties of the excited fluorophore in a process that takes 10–11 to 10–10 seconds. The solvent rearrangement effect is too slow to occur during absorption processes, and therefore absorption tends to be much less sensitive to solvent effects than is fluorescence. However, the excited state lifetime is easily long enough (usually ~10-9 seconds) to allow solvent rearrangement. The rearranged solvent stabilizes the excited fluorophore, and therefore lowers the overall energy of the system. However, when the fluorophore emits a photon to transition back to the ground state, once again the solvent molecules do not move during the process. As a result, the immediately reached ground state is higher in energy until the solvent molecules rearrange again. All of these factors mean that the wavelength of the fluorescence emission is usually longer than that of the absorbed radiation. Because the excited state that decays to the ground state is the same, the fluorescent spectrum is usually independent of the excitation wavelength.

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