What Are Fluorescent Molecules?

Fluorescent molecules emit lower-energy light after absorbing higher-energy radiation. Because of motion and collisions, not all molecules that could fluoresce do so. Fluorescent molecules can be synthesized as well as found naturally.

Fluorescent liquid in a glass.

Absorption and Emission

Fluorescent molecules absorb a short wavelength photon and release a longer wavelength photon of lower energy. Excess amounts are absorbed and transformed into rotation, vibration or translation (heat) motion of the molecule.

Fluorescence Lifetime

Absorption and emission isn't spontaneous and synchronized. Some molecules absorbing the short-wavelength photon will collide with others, thereby dissipating the absorbed energy in non-radiative steps before having a chance to fluoresce.

Quantum Yield

Quantum yield is a decimal between 0 and 1 indicating fraction of viable molecules that are observed to fluoresce. Quantum yield of 0.5 means half of fluorescent molecules in a sample emit light. The rest absorb the excess energy as heat or release it into the environment through nonfluorescent means.

Use and Exploitation

Understanding theory of fluorescence enables the manufacturing of fluorescent substances. Tracking biological substances such as ions, proteins or DNA segments is one among many practical applications of fluorescence.

Natural Occurrence

Chlorophyll, the substance that enables plants to use solar energy, undergoes fluorescence.

References

• San Diego State University. "Fluorescence"
• Dept. of Physics. University of Illinois Urbana-Champaign. "Fluorescence Lifetimes And How We Measure Them"
• Dept. of Chemistry. Rutgers University. "Fluorescence Spectroscopy"

Resources

• C&L Instruments Inc. "Applications: Fluorescence Systems"
• University of California, Los Angeles (UCLA). "Estimation of Chlorophyll Fluorescence"