Structure Property Relationship in Multi-Stimuli Responsive BODIPY-biphenyl-Benzodithiophene TICT† Rigidochromic Rotors Exhibiting (Pseudo) Stokes Shift up to 221 nm
Structure property relationships in three donor-π-acceptor (D-π-A) type rotor dyad (pp-AD) and triads (pp-ADA and Me-pp-ADA) based on benzodithiophene and BODIPY with biphenyl spacers have been reported. Rotors pp-AD and pp-ADA showed efficient twisted intramolecular charge transfer (TICT) with near infrared (NIR) emission at ~ 712 nm and ~ 725 nm with (pseudo) Stokes shift of ~ 208 nm and ~ 221 nm respectively and prominent solvatochromism. A structurally similar triad Me-pp-ADA with tetramethyl substituents on the BODIPY core instead was TICT inactive and exhibited excitation energy transfer with a transfer efficiency of ~ 88 % as revealed by steady state emission and transient absorption measurments. Rotors pp-AD and pp-ADA showed NIR emission with enhancement in intensity with the addition of water in THF solution as well as pronounced change in emission intensity with temperature and viscosity variation that justify their utility as temperature and viscosity sensors. Furthermore, linear correlation of lifetime with fluorescence intensity ratios of donor and acceptor justify the rigidochromic behaviour of these rotors.