Deciphering multiple energy-transfer photoevents in a 2D-MOF composite: relevance to multicolor lighting

Abstract

Incorporating different emitters within metal–organic frameworks (MOFs) allows tunable emission colors via energy transfer (ET) for desired and colorful lighting. Here in, we report on multiple dyes interacting with 2D hybrid MOF composed of Al clusters and 4-heptylbenzoic acid (HB) linkers (Al-ITQ-HB) exhibiting efficient ET from Coumarin 153 (C153) to Nile red (NR) and a broad emission spectrum. The C153@Al-ITQ-HB composites revealed emissions from adsorbed locally excited (0.15–0.25 ns), charge-separated (1.1–2.4 ns), and J-aggregates (3.4–5.7 ns) of C153 species along with a relatively fast homo-ET process (0.2–0.4 ns). However, in the C153/NR@Al-ITQ-HB composites, while the dual emission and time constant of the hetero-ET from C153 to NR weakly depend on C153 concentration, the photobehaviour strongly depends on the NR one and the hetero-ET times are longer (1.1–2.5 ns). Fluorescence lifetime imaging microscopy on single crystals shows homogeneous dye distribution within each crystal but different dye loading across different crystals of the same batch. These results highlight the impact of the donor–acceptor concentrations on ET within composites of two emitters, enabling tunable dual emissions for possible applications in lighting and optoelectronic devices.