Halogen-Bond-Assisted Photoluminescence Modulation in Carbazole-Based Emitter

Abstract

Halogen bonding between a carbazole-based, pyridine-substituted organic semiconductor and a common halogen-bond donor (pentafluoroiodobenzene) yields efficient halogen-bond-driven fluorescence modulation in solution. Steady-state, time-resolved emission and absorption spectroscopy as well as density functional theory studies demonstrate that the fluorescence modulation arises from halogen-bond-induced intramolecular charge transfer. Fluorescence modulation offers a range of possibilities both in solution and in the solid state, for instance providing a potential pathway for the design of tunable luminescent materials for light-emitting devices.

Halogen‐Bonded BODIPY Frameworks with Tunable Optical Features**

“…XBs are known for their highly tunable properties such as directionality, hydrophobicity, strength and length [16–20] . Moreover, XB interactions are known to enable efficient fluorescence or phosphorescence emission in chromophores by promoting electron delocalization, which allows singlet and triplet excitations to be harvested simultaneously [21–26] . These combined features make XBs an excellent tool for the rational design and engineering of crystals with tunable optical features [27] .…”

“…Another distinctive feature of XBs is that interaction of the large size of bond-donating atoms (bromine, iodine) with oxygen can promote efficient fluorescence or phosphorescence emission in the chromophore by promoting electron delocalization, which allows to harvest singlet and triplet excitations simultaneously. [26][27][28][29][30] These combined features make XBs an excellent tailoring tool for rational design and crystal engineering to effectively tune optical features. 31 Because of complex nature of halogen bonding, most crystal engineering designs are predominantly based on small molecular structures.…”

Rapid Identification of Halogen Bonds in Co‐Crystalline Powders via 127I Nuclear Quadrupole Resonance Spectroscopy

“…Halogen bonding is a non‐covalent interaction occurring between the area of elevated electrostatic potential associated with a region of depleted electron density on a halogen (halogen‐bond donor), named the σ ‐hole, and a nucleophilic center such as a Lewis base (halogen‐bond acceptor) . Over the last decades, halogen bonding has emerged as a versatile non‐covalent interaction for use in crystal engineering, pharmaceuticals, material sciences, and anion receptors, to name a few, with several reviews available on the subject . This interest can be attributed in part to favorable properties such as its tuneability and linearity .…”

Halogen Atom and Position Dependent Strong Enhancement of Solid‐State Fluorescence and Stimuli Responsive Reversible Fluorescence Switching

“…The integration of halogen, a heavy atom into fluorophore structure often increased excited state lifetime and used as a strategy to enhance spin‐orbit coupling and fabricate phosphorescent materials . The increase of phosphorescence and lifetime in halogen bonding co‐crystals were exploited for developing room‐temperature phosphorescent materials . The increase of atom size in 2‐phenyl benzoxazole fluorophore showed decrease of fluorescence intensity .…”