Solid-State Assembly and Photoluminescent Behavior of 5-(9H-Carbazol-9-yl)isophthalic Acid–Based Molecular Crystals Influenced by Solvents and Organic Counterparts

Molecular crystals with desirable structures and tunable photoluminescence are highly important for multiscenario field applications as lasers, sensors, and light-emitting devices. However, purposeful controls on the photoluminescence are still challenging because of the high sensitivity of molecular stackings to molecular structures and surroundings. Herein, solid-state assembly and photoluminescent behavior of nine 5-(9H-carbazol-9-yl) isophthalic acid (CzIp)-based molecular crystals have been crystallographically, spectroscopically, and theoretically investigated by incorporation with electron-deficient acceptors and polar solvent molecules. As compared to the self-aggregation of green-emissive CzIp, methanol-solvated CzIp-CH3OH and hydrated CzIp-H2O exhibit tailorable structural overlaps for the π-stacked CzIp–CzIp dimers, emitting high-energy cyan and blue fluorescence upon excitation by UV light. These blue-shifted emissions are from different local excited states of the π-stacked dimers. By contrast, six cocrystals with 1:1 and 2:1 stoichiometry and/or cocrystallized solvent are constructed, respectively, from the π–π stacked CzIp-acceptor or CzIp–CzIp pairs, which are assembled into one-dimensional ribbons (for CzIp-OFN, CzIp-TCNB, CzIp-DCTFB, and CzIp-TCNQ, OFN = octafluoronaphthalene, TCNB = 1,2,4,5-tetracyanobenzene, DCTFB = 2,3,5,6-tetrafluoro-1,4-dicyanobenzene, and TCNQ = 7,7,8,8-tetracyanoquinodimethane), two-dimensional sheet (for CzIp-DITFB, DITFB = 1,4-diiodotetrafluorobenzene), and discrete cyclic tetramer (for CzIp-TND, TND = 1,4,5,8-naphthalenetetracarboxdiimide) through intermolecular hydrogen- and halogen-bonding interactions. These cocrystals emit switchable emissions from quenched fluorescence to intense blue, green, orange, and near-infrared photoluminescence. Further structural comparisons and theoretical calculations demonstrate that the wide-range multicolor luminescence is either from the local excited state or from the charge transfer, in which the π-stacked donor–acceptor pair, suitable energy levels, and band gap, as well as rational hole–electron distributions, manipulate synergistically the charge transfer-induced photoluminescence. These findings offer in-depth insights into the relationships of molecular stackings and photoluminescence, advancing the development of organic luminescence crystals with desirable optoelectronic properties.