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

Abstract

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.