Luminescence of aniline blue in hydrophobic cavity of BSA

The fluorescence of aniline blue in the presence of bovine serum albumin (BSA) was investigated using total luminescence spectroscopy (TLS), fluorescence emission and synchronous fluorescence spectra. The fluorescence exhibits appreciable hypsochromic shift along with an enhancement in the fluorescence yield. It is suggested that the polarity-dependent twisted intramolecular charge transfer (TICT) process is responsible for the remarkable fluorescence sensitivity. The reduction in the rate of TICT in the hydrophobic interior of albumin leads to the increase of fluorescence yield. In BSA little rotation around N–C bond of aniline blue occurs during the excited state lifetime. Therefore, it could be concluded that aniline blue molecules have been included into the hydrophobic cavity of BSA and formed complex. The driving forces behind such association between the dye and biopolymer might include electrostatic attraction between ionic dye species and opposite charges on the biopolymer. In the synchronous fluorescence spectra of aniline blue when Δλ = 170 nm, dual fluorescence for aniline blue is observed, local excited state (LE) and TICT state, the relative fraction of the normal planar state increased quickly in low BSA concentration. It is indicated that hydrophobic pockets of BSA affected the LE-TICT equilibrium.