Ultrafast formation of exciplex species in dicyanoanthracene ZSM-5 revealed by transient emission and vibrational spectroscopy

The photo-physical properties of dicyanoanthracene (DCA) molecules adsorbed on the external surface of ZSM-5 zeolite, forming DCA@ZSM-5 composites, have been investigated by picosecond transient emission, femtosecond transient absorption infrared vibrational spectroscopy, steady-state UV–vis, and quantum chemistry calculations. Following the photoexcitation at 420 nm of DCA@ZSM-5, the formation of the localized, LE, excited S1 state of DCA emitting below 500 nm is observed. LE is rapidly and quasi-exclusively converted into two distinct exciplex species, EX1 and EX2, detected by their emission above 520 nm, with a lifetime of 5 ns and 20 ns, respectively. The different transient species can be identified by the frequency of the CN stretching vibration that is a marker of the charge delocalisation and that is peaking respectively at 2162 (LE), 2174 (EX1) and 2187 (EX2) cm−1. DFT and TD-DFT calculations further support the assignment. The results show that the external surface of zeolite is an appropriate playground for the development of novel photoactive host–guest materials.