Reversible control of energy transfer efficiency using thermoresponsive volume-phase-transition gel and application to luminescence chromism

Abstract

For poly-N-isopropylacrylamide (PNIPA) gels with lower critical solution temperatures (LCSTs), a slight temperature shift dramatically changes the water content inside the gel. Unless bonded chemically, hydrophobic molecules—such as polycyclic aromatic hydrocarbons (PAHs)—added to the PNIPA gel aggregate to form a separate phase when the gel is in the swollen state and diffuse into the gel in the dehydrated state. This phenomenon can be leveraged by incorporating PAHs with energy transfer capabilities, such as anthracene (AN) and tetracene (TE), within a PNIPA gel and using the hydration state of the gel to modulate the distance between these molecules. Using this strategy, we were able to promote energy transfer in the aggregated state and suppress it in the dehydrated state of the gel. The emission from the energy-acceptor TE was dominant under accelerated energy transfer conditions, whereas when energy transfer was suppressed, emission from the AN excited species was also observed. The reversible transfer of energy, controlled by water absorption and dehydration, resulted in unprecedented luminescence chromism.