Aggregation-induced emission (AIE)-active molecules bearing singlet oxygen generation activities: the tunable singlet-triplet energy gap matters.

Herein, a series of photosensitizers were constructed of α, ß and γ-isomers of terpyridine and the corresponding N-methylation derivatives. Benefiting from the tunable singlet-triplet energy gap and aggregation-induced emission characteristics, two-photon active photosensitizers L2b and L2c showed relatively strong intersystem crossing facilitating 1O2 generation and cell apoptosis with near-infrared excitation.