Stimuli-responsive triplet-triplet annihilation upconversion with guanidyl functionalized annihilators for enhanced ratiometric sensing of trace water in MeOH

Adding stimuli-responsiveness to TTA-UC is appealing as it provides a unique platform for biosensing and chemosensing. Here, we synthesized three guanidyl functionalized annihilators A-1 similar to A-3 for stimuli-responsive TTA-UC. The annihilator A-1 self-assembled into microparticles in aprotic solvent like THF, CHCl3 and toluene with the DPA units arranged in an ordered manner via the strong hydrogen bonding interactions between the guanidyl groups, which guaranteed effective energy migration of triplet excitons, thus, efficient TTA-UC with phi(UC) of 10.2% was observed in THF. While MeOH degraded the well-aligned aggregates, accompanied by the decrease of phi(UC) to 2.9%. For A-2 and A-3, weak UC emissions in all the investigated solvents were observed due to pi-pi stacking of anthracene core. Interestingly, the destroyed hydrogen-bonding network of A-1 was success-fully reconstructed by the addition of trace water with phi UC recovered from 2.9% to 9.2% when 3% water was added. We also found that the well-aligned aggregates significantly accelerated the TTA process but have no impact on the TTET process, thus, enhanced ratiometric sensing of trace H2O in methanol was achieved with the unchanged phosphorescence as the internal standard and a detection limit as low as 0.084% (v/v) was achieved.