Simon Pope Lecture 1

Introduction to Advanced Spectroscopy

• Course title: Advanced Spectroscopy

• Instructors: Kenneth Harris, Emma Richards, and self (photo physics and EPR focus)

• Module structure: Divided into thirds, equal distribution of topics between lecturers

Course Content Overview

• Photo physics: Focus on Electron Paramagnetic Resonance (EPR) spectroscopy

• Kenneth Harris: Structural technique, X-ray diffraction

• Integration of topics was attempted but found to work better as standalone sections.

Assessment and Expectations

• Historical performance: Good averages, last year

• Assessments: Workshop questions are take-home, individual work without peer consultation

• Workshop structure: Questions from each lecturer, designed as exam preparation

• Additional materials: PowerPoint slides and problem-solving resources available on Learning Central

Recommended Textbooks

• Specialized Texts: Mention of a luminescence spectroscopy "Bible" available in the library

• General Chemistry Texts: Suggested for foundational concepts relevant to the course material

Luminescence Spectroscopy

• Definition: Study of light emission from materials; focuses on detecting emitted photons

• Connection to Electronic Transitions: Absorption of light leads to electronic transitions, promoting electrons from ground to excited states

Basics of Electronic Transitions

• UV Spectroscopy: Sample absorbs specific wavelengths of light, promoting electrons to higher energy states

• Ground state vs. Excited state: Stable lower energy configuration vs. unstable higher energy configuration

• Relaxation process: Excited state returns to the ground state, emitting energy

• Photoluminescence: Specific term for light emission that occurs when excited states are created via light absorption.

Types of Luminescence

• Several methods to generate excited states: light absorption, chemical reactions, biological systems, etc.

• Key Terms:

  • Chromophore: Molecule that absorbs photons

  • Lumiphore: Molecule that can emit photons (generic)

  • Fluorophore and Phosphor: Specific types of lumiphores responsible for fluorescence and phosphorescence emissions, respectively.

Spectral Shifts

• Important for understanding emission bands: Bathochromic shifts (longer wavelengths, lower energy) and Hypsochromic shifts (shorter wavelengths, higher energy)

Applications of Luminescence

• Critical in fields like medicine, biology, and pharmaceuticals

• Sensitivity of luminescence spectroscopy: Can detect down to 10^{-9} molar concentrations (single molecule detection)

• Applications include:

  • DNA sequencing

  • Forensics

  • Live cell bioimaging

Course Plan

• Upcoming sessions: Basic principles, periodic table review, organic and transition metal systems, applications of photoluminescence

Understanding Photoluminescence

• Distinction from other luminescence types: Focus on light-initiated excited states

• Other forms: Chemiluminescence (light emission from chemical reactions), bioluminescence (biological reactions), and mechanically induced luminescence.

Energy Level Diagrams (Jablonski Diagrams)

• Diagrams illustrate the generation and relaxation pathways of excited states

• Key Phases in Diagram:

  1. Absorption of light (excitation)

  2. Internal conversion (vibrational relaxation)

  3. Emission pathways: radiation vs non-radiation relaxation

Measurement Techniques

• Comparison with UV absorption: Different setup for luminescence measurement

• Setup:

  • Monochromator to select excitation wavelength

  • Clear cuvette on all sides for detecting emitted light at right angles to excitation

  • Photomultiplier tube (PMT) for emission detection

• Data obtained: Emission spectrum (plot of emission intensity vs. wavelengths)

Types of Measurements

• Steady-state Measurements: Continuous illumination leads to a steady-state population of excited states

• Time-resolved Measurements: Pulsed light, measuring emission intensity over time, exponential decay observed

  • Emission Lifetimes: Short for fluorescence (nanoseconds), longer for phosphorescence (milliseconds)

Conclusion & Next Steps

• Course structure is intensive; further exploration of measurements and principles in upcoming classes.