FLUORESCENCE MONITORING OF POLYACRYLAMIDE HYDROGEL USING 4-AMINOPHTHALIMIDE

4-Aminophthalimide (4-AP) trapped in water-filled micropores of polyac rylamide (PAA) gel is studied using steady state and time-resolved emi ssion spectroscopy. The position of the emission maxima and the tempor al decay of 4-AP in the hydrogel indicate the presence of multiple mic roenvironments arising from the variation of the pore size. In PAA gel , the emission maximum of 4-AP exhibits a marked dependence on the wav elength of excitation and varies from 470 to 550 nm as lambda(ex) is v aried from 300 to 400 nm. Global lifetime analysis at various waveleng ths suggests the presence of two species of lifetime 1.34 and 7.21 ns with the relative amplitude of the short component increasing with an increase in the emission wavelength. The 550 nm emission band with a s hort lifetime (amplitude of the short component being 0.86) correspond s to an environment very similar to that of water. The 470 nm band wit h a much longer lifetime (amplitude of the long component, 0.85), howe ver, implies a medium far less polar than water that does not allow th e solvent-mediated proton transfer to occur. No dynamic Stokes shift, is observed, which implies that even inside the semirigid gel the wate r molecules relax at a very fast rate (<60 ps). It is also observed th at the rotational relaxation time of 4-AP in PAA gel is too fast to be detected in a picosecond setup.