Probes for monitoring protein aggregation with a variety of photophysical properties are of importance for the fundamental understanding of the aggregation process as well as for drug discovery. In this manuscript we report the photoluminescence response of the metal dipyridophenazine complex [Re(CO)(3)(dppz)(Py)](+) in the presence of aggregated A beta. [Re(CO)(3)(dppz)(Py)](+) shows an instantaneous increase in photoluminescence with fibrilar A beta (primary light-switching), and an unprecedented further increase in photoluminescence upon light irradiation at 362 nm (secondary light switching). The total increase in photoluminescence amounts to 105-fold, which we show can be used to monitor A beta aggregation in real time.