Luminescence Properties of 1,8-Naphthalimide Derivatives in Solution, in Their Crystals, and in Co-crystals: Toward Room-Temperature Phosphorescence from Organic Materials

Abstract

Crystalline 1,8-naphthalimide derivatives bearing a bromine atom at the 4-position and a 2-, 3-, or 4- methylpyridine at the imidic N-position have been synthesized, and their co-crystals with the coformer 1,4-diiodotetrafluorobenzene have been obtained via mechanochemistry. The structure of crystals and co-crystals has been characterized by means of X-ray diffraction and Raman and IR analysis. The luminescence properties of the derivatives have been explored both in solution and in their solid crystals and co-crystals. All of the compounds exhibit weak fluorescence in air-equilibrated solutions at room temperature and both fluorescence and phosphorescence at low temperature. In air-free solvent, all of the derivatives show phosphorescence at room temperature, at variance with the unsubstituted 1,8-naphthalimide model. Solid crystals display a red-shifted fluorescence with an increased emission quantum yield as compared to solution, whereas co-crystals show different behaviors. For all of the solid compounds, phosphorescence could be observed at room temperature by means of a gated detection. The dependence of the luminescence features of the solid materials on the intermolecular interactions that occur in the lattice is discussed.

How a Small Structural Difference Can Turn Optical Properties of π‐Extended Coumarins Upside Down: The Role of Non‐Innocent Saturated Rings

“…Emission decays were found to be multi‐exponential, and could be fitted by a bi‐exponential function with a good approximation (Table ). Detection of multi‐exponential decays is common in solid organic materials, and can be ascribed to inhomogeneous distribution of exciton traps, such as impurities or structural defects of the crystal . Compounds of the DBU series show, as main component of the decay, a lifetime ranging from 3 to 7 ns, whereas for the DBN series decays of few ns are accompanied by longer components of 10–20 ns.…”

Mechanochromic luminescence of halide-substituted difluoroboron β-diketonate dyes

“…This trend is commonly observed for halide substituted luminescent, aromatic organic compounds. 45,46 In Table S4 and Fig. S6, † it can be seen that the delayed emission maxima of all dyes change very little in response to mechanical force, while their pre-exponential weighted phosphorescence lifetimes increase dramatically.…”

Rational Design of Charge-Transfer Interactions in Halogen-Bonded Co-crystals toward Versatile Solid-State Optoelectronics

“…In this regard, co-crystallization opens up a door not only for synthesis of new multifunctional materials but also exploration of novel physical and chemical phenomena. It is appealing, however, the optoelectronic properties of organic co-crystals are focused very recently, [17][18][19][20][21][22][23] though the first co-crystal "quinhydrone" was already discovered by Wöhler in 1844, 24 while the definition of co-crystal was given and generally accepted since 2003. [25][26][27] This is partially because of many remained challenges in this direction, and one of them is achieving effective co-crystallization.…”