Investigation of Charge-Transfer Interaction in Mixed Stack Donor–Acceptor Cocrystals Toward Tunable Solid-State Emission Characteristics

The formation of three mixed binary charge transfer (CT) cocrystals with tunable photoluminescence behavior featuring both CT interaction and directional hydrogen bonding is presented. Our strategy consists of the CT induced cocrystallization of three polycyclic (naphthalene, anthracene, and pyrene) carrying α-cyanostilbene (CS) derivatives, namely, 3-(naphthalene-2-yl)-2-(p-tolyl) acrylonitrile (NPA), 3-(anthracene-9-yl)-2-phenylacrylonitrile (APA), and 2-(4-methoxyphenyl)-3-(pyrene-1-yl) acrylonitrile (MPA) as donors (D) with 1,2,4,5-tetracyanobenzene (TCNB) as an acceptor (A). The as-prepared cocrystals were probed in detail by various analytical techniques, namely, X-ray diffraction data, vibrational spectroscopy, diffuse reflectance absorption spectroscopy, fluorescence properties, and fluorescence quantum yields and lifetimes, affirming the formation of CT complexes. Complex IA features a mixed stack arrangement (D–A–D–A–D), while IIA and IIIA revealed (DAD---DAD) stack arrangement. The CT products showed distinct tunable emission colors and photoluminescence characteristics, which is closely associated with the CT interactions between the donor and acceptor moiety, and ionization potential or the π-electron rich character of the polycyclic moiety of the donor molecule. This research demonstrates the development of new hybrid CT functional materials with enhanced optical properties such as absorption, fluorescence emissions, and lifetimes compared to the pristine donors, which is important for the exploration of new solid-state luminescent materials