Studying the Impact of Water on Excited-State Dynamics of 2,5-Dimethylbenzoxazole

In solution, the surrounding solvent has a strong impact on how a molecule behaves after it absorbs light. To investigate how water affects the excited-state behavior of 2,5-dimethylbenzoxazole (DMBO), femtosecond transient absorption spectroscopy was used to study DMBO after excitation at 266 nm in two different solvent environments. Pure acetonitrile (ACN) and a mixture of ACN and water (ACN:H₂O) were used to assess the influence of water on the photophysical properties and excited-state dynamics of the DMBO. The results show that in ACN, the excited state of DMBO relaxes quickly, with a lifetime of about 56 ps. In contrast, the excited state lifetime increases to 670 ps in ACN:H₂O, which can be ascribed to change in solvent polarity upon the addition of water which stabilizes the excited state and slows down its decay. The present study clearly demonstrates that solvent composition significantly affects the photophysical processes of solutes, which may provide a new method to modify the chemical reactions.