PHD
  1. Inorganic chemistry  1.1. Coordination chemistry  1.1.1. Ligand field theory  1.1.2. Crystal field theory  1.1.3. Molecular Orbital Theory for Coordination Compounds  1.1.4. Stability of Coordination Compounds  1.1.5. Electronic spectra of coordination compounds  1.1.6. Isomerism in Coordination Compounds  1.1.7. Kinetics and mechanism of coordination reactions  1.2. Organometallic Chemistry  1.2.1. Metal Carbonyls  1.2.2. Metal alkyl and aryl  1.2.3. Fischer and Schrock carbonaceans  1.2.4. Oxidative Addition and Reductive Elimination  1.2.5. Metal Hydrides  1.2.6. Catalysis by organometallic compounds  1.2.7. Metallocenes and Sandwich Complexes  1.2.8. CH activation  1.3. Solid state chemistry  1.3.1. Crystal structures and lattices  1.3.2. Band theory and electrical properties  1.3.3. Defects in the crystal  1.3.4. Synthesis of solid state materials  1.3.5. Magnetic and optical properties of solids  1.3.6. Superconductivity  1.3.7. Solid state ionics  1.4. Bio-inorganic chemistry  1.4.1. Metalloproteins and enzymes  1.4.2. Metal ion transport and storage  1.4.3. The role of metals in medicine  1.4.4. Bioinspired catalysis  1.4.5. Metal–DNA interactions  1.4.6. Metal Complexes in Medical Science  1.5. Lanthanides and Actinides  1.5.1. Electronic configuration and oxidation states in lanthanides and actinides  1.5.2. Spectral and Magnetic Properties in Lanthanides and Actinides  1.5.3. Separation and Extraction of Lanthanides and Actinides  1.5.4. Coordination chemistry of f-block elements  1.6. Main Group Chemistry  1.6.1. Chemistry of boron compounds  1.6.2. Chemistry of Silicon and Germanium Compounds  1.6.3. Chemistry of Phosphorus and Sulfur Compounds  1.6.4. Organosilicon chemistry  1.6.5. Noble Gas Chemistry
  2. Organic chemistry  2.1. Reaction mechanism  2.1.1. Nucleophilic substitution reactions  2.1.2. Electrophilic addition and substitution reactions  2.1.3. Elimination reactions  2.1.4. Rearrangement reactions  2.1.5. Radical reactions  2.1.6. Pericyclic Reactions  2.1.7. Photochemical reactions  2.2. Stereoscopic  2.2.1. Chirality and optical activity  2.2.2. Structural analysis  2.2.3. Stereoelectronic effects  2.2.4. Asymmetric synthesis  2.2.5. Dynamic Stereochemistry  2.3. Organometallic Chemistry in Organic Synthesis  2.3.1. Organolithium and organomagnesium reagents  2.3.2. Transition metal catalyzed coupling reactions  2.3.3. Palladium-catalyzed reactions  2.3.4. Olefin Metathesis  2.3.5. Gold and silver catalysis  2.4. Natural products chemistry  2.4.1. Alkaloids and terpenoids  2.4.2. Steroids and Flavonoids  2.4.3. Total synthesis of natural products  2.4.4. Biosynthesis of natural products  2.5. Supramolecular Chemistry  2.5.1. Host-Guest Chemistry  2.5.2. Self-assembly and molecular recognition  2.5.3. Supramolecular Catalysis  2.5.4. Molecular Machines
  3. Physical Chemistry  3.1. Thermodynamics  3.1.1. Laws of Thermodynamics  3.1.2. Chemical Potential and Equilibrium  3.1.3. Statistical thermodynamics  3.1.4. Non-equilibrium thermodynamics  3.2. Quantum Chemistry  3.2.1. Schrödinger equation and its applications  3.2.2. Molecular orbital theory  3.2.3. Density functional theory  3.2.4. Post-Hartree–Fock methods  3.3. Chemical kinetics  3.3.1. Reaction rate theory  3.3.2. Mechanism and rate laws  3.3.3. Catalysis and enzyme kinetics  3.3.4. Reaction dynamics  3.4. Spectroscopy and molecular structure  3.4.1. Infrared Spectroscopy  3.4.2. UV-visible spectroscopy  3.4.3. Nuclear Magnetic Resonance Spectroscopy  3.4.4. Mass Spectrometry  3.4.5. Raman Spectroscopy  3.5. Surface and Colloid Chemistry  3.5.1. Absorption and Catalysis  3.5.2. Surfactants and micelles  3.5.3. Colloidal Stability  3.5.4. Nanomaterials and Interfaces
  4. Analytical chemistry  4.1. Chromatography  4.1.1. Gas Chromatography  4.1.2. High Performance Liquid Chromatography  4.1.3. Thin Layer Chromatography  4.1.4. Ion Chromatography  4.2. Electroanalytical techniques  4.2.1. Voltammetry and Polarography  4.2.2. Conductometry and potentiometry  4.2.3. Colometry  4.3. Spectroscopic Methods  4.3.1. Atomic absorption spectroscopy  4.3.2. Fluorescence Spectroscopy  4.3.3. X-ray diffraction  4.3.4. Electron paramagnetic resonance spectroscopy  4.4. Chemometrics  4.4.1. Data processing and statistical methods  4.4.2. Multidisciplinary analysis  4.4.3. Machine Learning in Analytical Chemistry
  5. Theoretical and Computational Chemistry  5.1. Molecular dynamics simulation  5.2. Quantum chemistry methods  5.3. Computational drug design  5.4. Machine Learning in Chemistry  5.5. Ab initio molecular dynamics
  6. Biophysics and Medicinal Chemistry  6.1. Drug discovery and design  6.2. Enzyme kinetics and inhibition  6.3. Chemical biology approach  6.4. Protein-ligand interactions  6.5. Bioorthogonal chemistry
  7. Materials chemistry  7.1. Polymer chemistry  7.1.1. Polymerization mechanism  7.1.2. Functional Polymers  7.1.3. Biodegradable Polymer  7.1.4. Conducting and semiconducting polymers  7.2. Nano Chemistry  7.2.1. Nanoparticles and nanostructures  7.2.2. Carbon-based nanomaterials  7.2.3. Quantum dots  7.3. Energy and Environmental Chemistry  7.3.1. Battery and Fuel Cell Chemistry  7.3.2. Green chemistry and sustainable materials  7.3.3. Photocatalysis

PHD → Analytical chemistry → Spectroscopic Methods ↓


Fluorescence Spectroscopy


Fluorescence spectroscopy is a type of electromagnetic spectroscopy that analyzes fluorescence from a sample. It involves using a beam of light, usually UV light, to excite electrons in the molecules of certain compounds and cause them to emit light; this emitted light is often at a longer wavelength than the absorbed radiation.

Basic principles

The process of fluorescence can be understood by studying the Jablonski diagram:

    S2 │ excited │
       │ State │
               
    S1 │ excited │
       │ State │
         
    __  __
      /
       /
       /
       
    S0 │ Ground │
       │ State │

When a molecule absorbs a photon, it goes from a ground state (S0) to an excited state (S1 or S2). This transition occurs in about 10-15 seconds and is marked by the absorption of energy. After being excited, the molecule relaxes and falls to the lowest vibration level of S1. This process, called internal conversion, is usually faster than other processes.

The molecule can return to its ground state in a few ways. One possibility is by emitting a photon; this is fluorescence. Generally, the emitted light has a longer wavelength than the absorbed light because of some energy loss during non-radiative decay.

Properties of fluorescence

Fluorescence spectroscopy provides various noteworthy properties:

  • Quantum yield: The ratio of the number of photons emitted to the number of photons absorbed. A high quantum yield indicates that most of the absorbed photons result in emitted fluorescence.
  • Stokes shift: The difference in wavelength between the positions of the band maxima of the absorption and emission spectra. This is important for fluorescence detection because it gives the difference between the excitation and emission wavelengths, thereby reducing noise.

Applications of fluorescence spectroscopy

Fluorescence spectroscopy is widely used in various fields due to its high sensitivity and selectivity:

1. Biochemistry: It is used to study proteins, nucleic acids, and other biomolecules. For example, researchers can use amino acids such as tryptophan or tyrosine, which are naturally fluorescent, to study protein structure.

2. Medical diagnosis: Fluorescence techniques are widely used in medical diagnosis (e.g., flow cytometry, fluorescence microscopy) to identify and quantify biomolecules or cells.

3. Environmental studies: The presence of pollutants, toxins or other environmental parameters can be monitored efficiently using fluorescent methods, such as oil spill detection with fluorescent dyes.

4. Forensic analysis: The ability to detect small quantities of substances makes fluorescence spectroscopy invaluable in forensic investigations.

Instrumentation of fluorescence spectroscopy

A typical fluorescence spectrometer consists of several basic components:

  • Light source: The source must provide sufficient intensity. Typically, xenon or mercury lamps are used; these emit broad spectrum light. In modern spectrometers, lasers or LEDs are also used for excitation.
  • Excitation monochromator or filter: It isolates a specific excitation wavelength to avoid interference from other wavelengths.
  • Cuvette: The sample is contained here. Cuvettes are usually made of glass, quartz, or plastic and must have a flat surface and optical-quality surface.
  • Emission monochromator or filter: This isolates the fluorescence light emitted from the sample and removes any scattered excitatory light.
  • Detectors: Typically, photomultiplier tubes (PMTs) are used to detect and measure the light intensity. Other detectors such as photodiodes or CCD cameras are also used.

Visual representation of fluorescence spectroscopy

Below is a simplified visual representation of fluorescence spectroscopy in action:

    │ light │ __ __ │ │ __ ____ │ emitter │__ __
    │ source │/ /  │ stimulation │/ / │ / / 
    └────────────┘ │ mono- │ └──────────┘
                             │ Chromatator/ │
                             │ Filter │
                             
                 
                 │Sample (cuvette)│ │
                 │ < stimulation │ emission > │
                 
                             
                             │ Emission │
                             │ mono- │
                             │ Chromatator/ │
                             │ Filter │
                             
                             │Detector │

Advantages of fluorescence spectroscopy

1. Sensitivity: This technique is extremely sensitive and can detect substances at very low concentrations, often as low as parts per billion (ppb).

2. Selectivity: Different excitation and emission wavelengths make it possible to selectively analyze specific compounds, even in complex mixtures.

3. Non-destructive: Samples can often be analyzed without any consumption or destruction.

Limitations of fluorescence spectroscopy

1. Quenching: Certain conditions or compounds can interfere with the fluorescence process, reducing the intensity - this is called quenching. Typical quenchers include oxygen, heavy metals, and other chemicals.

2. Interference: Scattering from the sample or container can introduce noise and complicate the measurement.

3. Photobleaching: Prolonged exposure to excitation light can degrade the sample, permanently reducing fluorescence.

Future trends

Advances in technology continue to enhance the applications of fluorescence spectroscopy. For example, the integration of fluorescence spectroscopy with electronic and optical technologies allows the development of miniaturized, portable instruments with rapid, on-site testing capabilities.

Applications in high-throughput screening and in-vitro diagnostics are expanding, with innovations such as single-molecule fluorescence microscopy achieving unprecedented levels of detail and understanding in chemical and biochemical systems.

Overall, fluorescence spectroscopy remains an invaluable tool in modern scientific research, with vast potential for future discovery and technology development.


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Fluorescence Spectroscopy

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