Molecular Luminescence Spectroscopy Flashcards

1
Q

Forms of Luminescence (8)

A

Radio
Electro
Thermo
Tribo
Sono
Photo
Chemi
Bio

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2
Q

Jablonski Diagram Components (6)

A

Vibrational Relaxation
Internal Conversion
Fluorescence
Phosphorescence
Intersystem Crossing
External Crossing

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3
Q

a molecule of analyte absorbs a photon and excites a species in a process called photo-excitation

A

photoluminescence

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4
Q

no excitation radiation source; molecules of analyte are excited via chemical reaction to give a species whose emission spectrum provides information for quali/quanti analyses

A

chemiluminescence

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5
Q

Nonradiative deactivation in Jablonski Diagram

A

Vibrational Relaxation
Internal Conversion
Intersystem Crossing
External Conversion

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6
Q

Radiative Deactivation in Jablonski Diagram

A

Fluorescence
Phosphorescence

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7
Q

collisions of excited state analyte molecules with other molecules lead to loss of excess vibrational energy

A

vibrational relaxation

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8
Q

molecule passes to a lower energy state, vibrational energy levels of two electronic states overlap and molecules pass from one electronic state to other

A

Internal conversion

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9
Q

Spin of electron is reversed leading to change from singlet to triplet state

A

Jntersystem Crossing

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10
Q

Interaction and energy transfer between the excited molecules and the solvent or other molecules

A

External Conversion

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11
Q

emission of a photon via a singlet to singlet transition

A

fluorescence

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12
Q

emission of a photon via a triplet to singlet transition

A

Phosphorescence

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13
Q

all electron spins are paired; no energy level splitting occurs when the molecule is exposed to EMF

A

singlet

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14
Q

unpaired and parallel electron spins; excited state is less energetic than the corresponding state

A

Triplet

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15
Q

no net magnetic field due to spin pairing; electrons are repelled by permanent magnetic fields

A

Diamagnetic

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16
Q

magnetic moment and attracted to a magnetic field

A

paramagnetic

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17
Q

Types of fluorescence (2)

A

Resonance Fluorescence
Non-Resonance Fluorescence

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18
Q

absorbed radiation is re-emitted without a change in frequency and wavelength

A

Resonance Fluorescence

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19
Q

molecular fluorescence bands are shifted to wavelengths that are longer than the resonance line

A

non-resonance fluorescence

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20
Q

Factors affecting luminescence (7)

A

Quantum Yield
Molecular Structure
Structural rigidity
Dissolved oxygen
temperature
solvent
pH

21
Q

Quantum yield formula

A

total no. luminescing molecules/ total no. of excited molecules

22
Q

occurs when a molecule changes from higher electronic stage to an upper vibrational level of a lower electronic state in which the vibrational energy is strong enough to rupture the bond

A

Predissociation

23
Q

occurs when radiation promotes a molecule directly to a state with sufficient vibrational energy for a bond to break

A

Dissociation

24
Q

compounds that do not fluoresce have structures that ____

A

permit rapid relaxation by nonradiative processes

25
Q

what increases fluorescence intensity? (3)

A

increasing benzene substituents,
decreasing molar mass of substituents, increasing substitution in oxygenated species

26
Q

Flexibility increases, quantum yield?

A

decreases

27
Q

____ in a molecule causes an enhanced internal conversion rate and a consequent increase in likelihood for nonradiative deactivation

A

lack of rigidity

28
Q

Luminescence favored in molecules with ___ structures

A

rigid

29
Q

Presence of dissolved oxygen, ___ fluorescence

A

reduces

30
Q

Luminescence favored ____ temperatures

A

lower

31
Q

___ solvent is preferred in luminescence

A

polar

32
Q

luminescence preferred more ____ solvents

A

viscous

33
Q

Fluorescence and Phosphorescence relationship

A

inverse

34
Q

Fluorescence ____ if solvents contain heavy atom

A

decreases

35
Q

two thoriated tungsten made electrodes are placed face to face with a small gap in an airtight transparent envelope of fused silica filled with xenon gas in very high pressure

A

xenon arc lamp

36
Q

LASERS

A

Light Amplification by Stimulated Emission of Radiation

37
Q

LIF

A

Laser Induced Fluorescence

38
Q

determined by scanning the excitation monochromator in a range less than the preset wavelength of the emission monochromator

A

excitation spectrum

39
Q

excitation monochromator is adjusted at the determined lambda ex and emission spectrum is scanned

A

emission spectrum

40
Q

Usually the detector is set at ___ to the incident beam

A

90°

41
Q

PMT

A

photomultiplier tube

42
Q

CCD

A

charge-coupled devices

43
Q

Techniques in Molecular Luminescence Spectroscopy (3)

A

Molecular fluorescence spectroscopy
Molecular phosphorescence spectroscopy
Chemiluminescence spectroscopy

44
Q

Fluorometer: Hg Lam and Interference filter

Spectrofluorometer:

A

xenon lamp and diffraction grating monochromator

45
Q

excited molecules lose their energies by collisions with other molecules of solvent

A

self-quenching

46
Q

when an emission ban overlaps woth an excitation, emitted photons excite other molecules in the ground state which results in no net emission

A

self-absorption

47
Q

sample tubes that are placed in liquid nitrogen held in a quartz Dewar flask

A

phosphoroscope

48
Q

produced when a chemical reaction yields an electronically excited species, which emits light as it returns to its ground states

A

chemiluminescence