Advanced Studies of Anthracene Containing Squaraine Rotaxanes

Squaraine dyes are bright, organic fluorophores that are susceptible to nucleophilic decomposition due to their highly electron-deficient cores. Tetralactam macrocycles have been employed to sterically protect the encapsulated squaraine, resulting in improved chemical and photochemical stability. These [2]rotaxanes, termed squaraine rotaxanes (SR), are versatile supramolecular architectures and can be used as fluorescent dyes for optical imaging purposes. This dissertation represents the continued study of anthracene containing SR derivatives and explores their potential applications as optical imaging agents. The thesis begins with the development of a SR for optical anion detection. A hydroxylated SR architecture is developed that selectively and ratiometrically detects chloride anions. Chloride induces lateral displacement of the macrocycle away from the stabilized squaraine core, resulting in a 30-40 nm shift in absorption/fluorescence maxima that allows for naked-eye detection of analyte. The rotaxane sensor reversibly binds chloride and dipsticks containing the sensor can be used in aqueous environments. The thesis next describes SR endoperoxides (SREP), storable SR analogues that emit light as they cleanly release singlet oxygen. SREPs are produced by photooxygenation of anthracene-containing SR dyes. Chapter three discusses experimental and computational results that demonstrate that the initial, kinetic photooxygenation product of is the strained external SREP stereoisomer, with the endoperoxide unit directed outside the macrocycle. The photophysical properties and subsequent reactivity of mechanically strained external SREP depend on the size of the end groups of the encapsulated squaraine. The thesis then addresses efforts to tune emission wavelength and improve the brightness of SREP light output. Using a truncated, green-emitting squaraine template, SREP chemiluminescence becomes green, which demonstrates that the emission comes from the excited squaraine inside the macrocycle cavity. Oligomeric SREP derivatives were prepared but they did not lead to higher chemiluminescence intensities. The thesis concludes with the development of several new SR architectures that expand the SR library into the orange/red region of the emission spectrum. While chemiluminescent analogues were not prepared, the work is a step forward toward the goal of a red-emitting chemiluminescent SREP derivative.