Photochemistry is a discipline that studies the interaction between light and matter with the scope to induce chemical transformations. The first conjugation between light and chemistry can be dated back to the lifespan of Giacomo Luigi Ciamician, who is considered to be one of the founders and pioneers of photochemistry. In the ensemble of photochemical reactions and of photosensitive compounds discovered so far, molecular switches are compounds with such promising features to be included in the Nobel prize for chemistry assigned in 2016. Indeed, in these works, molecular machines were actioned by combinations of thermal and photochemical stimuli managing to move these machines in a defined direction. The interest in this field is expanding as well in the domain for energy conversion. As matter of fact, it is possible to find a major contribution of photochemistry in the development of semiconductor-based solar panels. These devices are widespread and are contributing to the reduction of the emission of pollutants in the atmosphere. The solar panels, for instance, are deriving from the extensive study of the interaction between light and the materials that compose the panels themselves. Another subject that is pivoting around photochemical processes is biochemistry. Converting sunlight into chemical energy is a process that plants and photosynthetic organisms perform every day for all their lifespan with great efficiency. Based on these inspirations, scientists have always demonstrated the ambition to mimic and reproduce photosynthesis, a complex yet fascinating natural process. Moreover, the abundance of solar irradiation on earth makes technologies for solar power conversion a central point around which current research is orbiting. In this key and with the inspiration mentioned above, the thesis treats synthesis and description of benzo indolino pirano spyran (BIPS) photoacids, compounds able to react to the presence of visible light by releasing protons. Many implications of their photoacidity have been already reported in the past as for photolithography, biochemistry and smart materials (i.e., soft robotics) to mention some. These compounds represent a class of photoswitches which displays a broad set of interesting applications, nevertheless their photoacidity was never subject of extensive studies from the physico-chemical point of view. The accumulation of chemical energy in the form of acidity gradients represents an interesting potential derivation of BIPS; these bear all the chemical photochemical characteristics to be excellent candidates in this task. In the first part of this elaborate will be discussed the background, the applicability, and the most relevant studies on the chemistry of BIPS in water. The third chapter will cover the formulation of a working mechanism and the design of a generally applicable quantitative characterization protocol for the (photo)chemistry of BIPS photoacids in water using a combination of different physico-chemical techniques. The fourth chapter describes the temperature dependency of the chemistry of BIPS photoswitches in water. Altering the environmental variables for improving the performance of BIPS photoswitching is an aspect that was not described in detail in the past. In this chapter, the focus is to exploit temperature differences for maximizing the photoacidity (and the performances in general) of BIPS. The fifth chapter will cover the functionalization of BIPS with EDGs and th