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20 Cards in this Set

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fluorescence
Fluorescence is the emission of visible light by a substance that has absorbed light of a different wavelength.

In most cases, absorption of light of a smaller wavelength induces emission of light with a larger (less energetic) wavelength
phosphorescence
Phosphorescence does not immediately re-emit the radiation it absorbs. The slower time scales of the re-emission are associated with "forbidden" energy state transitions in quantum mechanics (electron spin pairing)
singlet state
A transient, excited state of a molecule upon absorbing light that can release energy as heat or light (fluorescence) and thus return to the initial (ground) state

electrons remain paired
triplet state
A second excited state of a molecule produced by absorption of light to produce the singlet state, then loss of some energy (fluorescence) to arrive at the longer-lived triplet state The molecule may remain sufficiently long in the triplet state for a second activating light quantum to be effective in producing a second triplet state, obviously at still a higher level of excitation, hence reactivity. Alternatively, it may lose the triplet state energy directly and return to the ground state.

Electrons unpaired
vibrational relaxation
A process in which a polyatomic molecule in an excited vibrational state returns to a lower vibrational state in the same electronic state by colliding with other molecules

Energy given off as heat
internal conversion
a transition from a higher to a lower electronic state in a molecule. It is sometimes called "radiationless de-excitation", because no photons are emitted. It differs from intersystem crossing in that, while both are radiationless methods of de-excitation, the molecular spin state for internal conversion remains the same, whereas it changes for intersystem crossing. The energy of the electronically excited state is given off to vibrational modes of the molecule. The excitation energy is transformed into heat.

vibrations of molecule cause loss of energy through heat
external conversion
collisions with other molecules cause loss of energy
intersystem crossing
When a singlet state nonradiatively transitions to a triplet state, that process is known as intersystem crossing. In essence, the spin of the excited electron is reversed. The probability of this process occurring is more favorable when the vibrational levels of the two excited states overlap, since little or no energy must be gained or lost in the transition
quantum yield
fraction of emitted phtons/fraction of absorbed photons
hypsochromic
a change of spectral band position in the absorption, reflectance, transmittance, or emission spectrum of a molecule to a shorter wavelength (higher frequency)

aka blue shift

seen in molecular spectra, not atomic spectra
bathochromic
a change of spectral band position in the absorption, reflectance, transmittance, or emission spectrum of a molecule to a longer wavelength (lower frequency)

aka red shift
hyperchromic
an increase in the intensity of a spectral band due to a change in the molecular environment
hypochromic
a decrease in absorption intensity
conjugated
a sequence of alternating double (or triple) and single bonds. [E.g. C=C-C=C and C=C-C=O. Conjugation can also be relayed by the participation of lone pairs of electrons or vacant orbitals.]
Lipinski's Rule of Five
1. fewer than 5 H bond donors
2. fewer than 10 H bond acceptors
3. molecular weight of less than 500
4. logP value of less than 5
bathochromic
a change of spectral band position in the absorption, reflectance, transmittance, or emission spectrum of a molecule to a longer wavelength (lower frequency)

aka red shift
hyperchromic
an increase in the intensity of a spectral band due to a change in the molecular environment
hypochromic
a decrease in absorption intensity
conjugated
a sequence of alternating double (or triple) and single bonds. [E.g. C=C-C=C and C=C-C=O. Conjugation can also be relayed by the participation of lone pairs of electrons or vacant orbitals.]
Lipinski's Rule of Five
1. fewer than 5 H bond donors
2. fewer than 10 H bond acceptors
3. molecular weight of less than 500
4. logP value of less than 5