Unusual Aggregation‐Induced Emission of a Coumarin Derivative as a Result of the Restriction of an Intramolecular Twisting Motion

Abstract

Aggregation-induced emission (AIE) is commonly observed for propeller-like luminogens with aromatic rotors and stators. Herein, we report that a coumarin derivative containing a seven-membered aliphatic ring (CD-7) but no rotors showed typical AIE characteristics, whereas its analogue with a five-membered aliphatic ring (CD-5) exhibited an opposite aggregation-caused quenching (ACQ) effect. Experimental and theoretical results revealed that a large aliphatic ring in CD-7 weakens structural rigidity and promotes out-of-plane twisting of the molecular backbone to drastically accelerate nonradiative excited-state decay, thus resulting in poor emission in solution. The restriction of twisting motion in aggregates blocks the nonradiative decay channels and enables CD-7 to fluoresce strongly. The results also show that AIE is a general phenomenon and not peculiar to propeller-like molecules. The AIE and ACQ effects can be switched readily by the modulation of molecular rigidity.

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

“…The above‐mentioned analysis contrasts with the recent considerations, in which n orbitals were deliberately excluded from the active space.…”

A Light‐up Logic Platform for Selective Recognition of Parallel G‐Quadruplex Structures via Disaggregation‐Induced Emission

“…Among those, coumarin‐based compounds are considered archetypical dyes with a unique combination of both valuable optical properties and biological compatibility along with the tendency to form well‐defined supramolecular architectures . However, in many conventional systems, the typical co‐facial π‐stacking arrangements of self‐assembled luminophores, even at sub‐micromolar concentrations, results in a partial or complete suppression of the emissive properties via relaxation of the excited‐states through non‐radiative channels (aggregation‐caused quenching, ACQ) . From the viewpoint of real‐life applications, this process hampers the widespread applicability of these types of optical probes and sensors, especially in the bio‐sensing arena.…”

Fluorescence enhancement in crystals tuned by a molecular torsion angle: a model to analyze structural impact

“…[1][2][3][4][5] Molecules that exhibit this phenomenon include cruciforms, 6 hexaphenylsilole, 7 diaminodicyanoquinodimethanes (DADQs), 8 diphenylbutadienes 9 and tetraphenylethenes. 12 Even though some computational studies have probed the role of intramolecular excited state relaxation, 1,13 a coherent picture of the intra and intermolecular factors that together lead to the emission enhancement is yet to be established; the latter in particular has not been examined in any detail. Extensive studies have focused on the development and application of molecules exhibiting very high enhancement factors; extension of a tetraphenylethene core by adding the same moiety is a typical example.…”