Emergence of aggregation induced emission (AIE), room temperature phosphorescence (RTP) and multi-stimuli response from a single organic luminogen by directed structural modification

Metal free multi-functional organic luminogens exhibiting simultaneous aggregation induced emission (AIE), room temperature phosphorescence (RTP) and mechanochromism have attracted widespread interest. However, luminogens showing AIE and mechanochromic properties are often conventional fluorophores with lifetime in nano-second time scale1, 2 and designing such type of multi-functional luminogens have often met with limited success. Herein, starting from an ACQphore TPANDI, by simple structural engineering we have demonstrated a route to obtain multi-functional organic luminogen like-TPACNPMI with AIE, mechanochromic and as well as RTP properties. We have shown that a slight reduction in size of the planar acceptor moieties can effectively inhibit the π-π stacking interaction between molecules in condensed state and can bring about a ACQ to AIE type transformation from TPANDI to TPANMI and TPAPMI. Both TPANMI and TPAPMI are AIEgens with RTP properties in ambient condition due to presence of a very low singlet-triplet energy gap ∆EST. Unfortunately, these two luminogens are mechano-inactive but an insertion of cyano-ethylene group and benzene linker in between the triphenyl amine and phthalimide moieties can solve this problem and can give birth to a luminogen, TPACNPMI that can simultaneously exhibit AIE, RTP and mechanochromic properties