Temperature and pH sensitive photoluminescence of riboflavin-methyl cellulose hydrogel: towards AND molecular logic gate behaviour

Abstract

The photoluminescence (PL) of riboflavin-methyl cellulose hydrogel is 93 fold enhanced in the gel state compared to that in the sol state at pH ≤7. AND molecular logic gate like behaviour is observed using temperature and pH as inputs and enhanced PL of riboflavin as the output. Thermal gelation of methyl cellulose at higher temperatures (>50 °C) produces hydrophobic core entrapping riboflavin molecules at the fibrillar junction points inhibiting the non-radiative decay of exitons by the solvent molecules. This causes a dramatic increase of PL intensity at pH ≤ 7 in the gel state compared to that of the sol state. But at pH 9 the PL intensity reduces to 1/3 of the value of that of pH 7 at 85 °C because the labile proton of imido group becomes ionized hampering the conjugation of isoalloxazine ring causing PL quenching. So below the gelation temperature (<50 °C) of methyl cellulose and pH higher than 7 are ‘0’ state and temperature >50 °C and pH ≤7 are ‘1’ state. Thus a semi solid AND logic gate like system is demonstrated using a riboflavin–methyl cellulose hydrogel and the reversibility of the logic gate action is examined with respect to both the temperature and pH of the system.