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.