Segregating the Orange Emission of Perylene in the Solid State into Blue and Yellow in Its Composites with Zeolitic Imidazolate Framework-8 Metal–Organic Frameworks: A Spectrodynamic Investigation

In this work, we report the detailed spectrodynamic investigation of two composites of benchmark fluorophore perylene with metal-organic framework (MOF) zeolitic imidazolate framework-8 (ZIF-8), with the latter being widely used to encapsulate fluorophores. The two composites were named ^encP@ZIF-8 and ^absP@ZIF-8. ^encP@ZIF-8 was obtained by encapsulating perylene within ZIF-8, whereas ^absP@ZIF-8 was obtained by absorbing perylene onto ZIF-8. Steady-state and picosecond-nanosecond (ps-ns) emission lifetime experiments revealed that perylene behaves as a solid diluted solution with the monomeric emission contributing at a maximum to the excited-state photophysics of ^encP@ZIF-8 with minute contributions from the excimer and emission from the H-aggregates. On the other hand, the excited-state photophysics of ^absP@ZIF-8 had contributions from J- and H-aggregates and excimer. ^encP@ZIF-8 and ^absP@ZIF-8 are cyan blue and yellow emitters, respectively, whereas pristine perylene is a prominent orange emitter in the solid state and a blue emitter in solution. Hence, differential incorporation of perylene onto ZIF-8 MOFs could enable us to obtain blue and yellow emitters, which was otherwise impossible to obtain from a pristine perylene molecule. The current work thus acts as a guide to generate differently emitting fluorophore@MOF composites for various optoelectronic applications by altering the mode of incorporation as well as understanding their photodynamics.