Light-activated "cycle-reversible intramolecular charge transfer" fluorescent probe: monitoring of pHi trace change induced by UV light in programmed cell death.

Under the synergistic effects of protonation and deprotonation, a light-activated fluorescent probe (UV-SP) exhibited "cycle-reversible intramolecular charge transfer (ICT)" for different pH after activation by UV light, resulting in emission of multiple ratio fluorescent signals (FI563/FI595 and FI664/FI595). Based on these kinds of response signals, UV-SP can specifically monitor the cycle-reversible trace change of intracellular pH caused by UV radiation. More importantly, according to the stable and invariant multiple ratio fluorescent signals, UV-SP can sort cells entering programmed death.