Photoacoustic calorimetry: Photochemistry/photophysics without a photon detector

Radiative channels of the photoexcited molecules are the avenues of the photoscientists for exploring the intricacies of various photoinduced processes. Non-emitting species are discouraging in that context. With a capability of monitoring the non-radiative deactivation, photoacoustic calorimetry (PAC), comes forward as a boon to rescue the scientists in such blocked tracks. Although the technique has some other acronyms like laser-induced optoacoustic spectroscopy (LIOAS), laser-induced optoacoustic calorimetry (LIOAC) and photoacoustic spectroscopy (PAS), PAC is the most used term. The rather new technique, flourished in the last three decades, has now been powerful enough to explore successfully many of the photophysical aspects that were not possible from the conventional spectroscopy. The interesting point is that PAC is effective only when it works hand-in-hand with the conventional spectroscopy and often serves as a complementary tool to the other. In this colloquium, the principle of the technique will be discussed at the fundamental level along with a demonstration of some of its applications in the field of photophysics/photochemistry.