A classic example of this process is the quinine sulfate fluorescence, which can be quenched by the use of various halide salts. The excited molecule can de-excite by increasing the thermal energy of the surrounding solvated ions.
Several natural molecules perform a fast internal conversion. This ability to transform the excitation energy of photon into heat can be a crucial property for photoprotection by molecules such as melanin. Fast internal conversion reduces the excited state lifetime, and thereby prevents bimolecular reactions. Bimolecular electron transfer always produces a reactive chemical species, free radicals. Nucleic acids (precisely the single, free nucleotides, not those bound in a DNA/RNA strand) have an extremely short lifetime due to a fast internal conversion.
Both melanin and DNA have some of the fastest internal conversion rates.
In applications that make use of bimolecular electron transfer the internal conversion is undesirable. For example, it is advantageous to have a long-lived excited state in Grätzel cells (Dye-sensitized solar cells).