Preservation of Photoluminescence Efficiency in the Ordered phases of Poly(2,3-diphenyl-1,4-phenylenevinylene) via Disturbing the Intermolecular π–π Interactions with Dendritic Aliphatic Side Chains

Abstract

To understand the relation between the solid-state phase structures and the photophysical properties of poly(2,3diphenyl-1,4-phenylenevinylene) (DP-PPV) derivatives, three DP-PPV derivatives, P1−P3, were designed, synthesized via Gilch polymerization and characterized. Among the polymers, P1 is a reported highly emissive poly(2,3-diphenyl-5-hexyl-pphenylenevinylene), and P2 and P3 are novel DP-PPV derivatives, which are purposely designed to bear hydrophobic and hydrophilic Percec-type dendrons as side chains. The bulkiness and hydrophobic−hydrophilic natures of the side chains show strong effects on photophysical properties of the polymers. The solutions and as-casted films of P1−P3 all show remarkably high photoluminescence (PL) efficiency (Φ PL ) (>80% in chloroform solution, and >63% for the as-casted films). However, Φ PL of P1 and P3 decrease significantly to 30% after cooled their polymer melts to room temperature. Through the phase behavior analysis by differential scanning calorimetry (DSC), and phase structure analysis by wide-angle X-ray diffraction (WAXD), the decrease of Φ PL can be elucidated and attributed to the ordering of the solid-state structures of P1 and P3. To our surprise, Φ PL of P2 is preserved even in an ordered solid-state phase, and it is insensitive to the structural ordering. Structural analysis of P2 revealed that the aliphatic dendritic side chains of P2 effectively disturbing the intermolecular π−π interactions among the conjugated backbones, which allows the preservation of Φ PL in the environment with ordered packing of DP-PPV molecules. The results of time-resolved PL decay experiments also confirmed that P2 possesses long-lived decay time because of excitons confined more effectively for emissive relaxation.

Synthesis, Aggregation-Induced Emission, and Liquid Crystalline Structure of Tetraphenylethylene–Surfactant Complex via Ionic Self-Assembly

“…However, most conventional luminogens are highly emissive in solution but will be weak or be quenched in the aggregated state due to the aggregation-caused quenching (ACQ) effect, − which ultimately limits the use of luminophores in optoelectronic devices. To overcome this shortcoming, various molecular strategies are used to avoid the quenching configurations in solid state. − For example, we and other laboratories have demonstrated that bulky substituents can disturb the stacking of conjugated luminophores and maintain light emission even in solid state. − Nevertheless, the light emission is often enhanced at the expense of long-range-ordered supramolecular structure, thus making the synthesis of mesomorphic materials with efficient exciton emission still a daunting task.…”

Ionic Self‐Assembled Derivative of Tetraphenylethylene: Synthesis, Enhanced Solid‐State Emission, Liquid‐Crystalline Structure, and Cu2+ Detection Ability

“…Unfortunately, serious problems associated with most fluorophores are their intrinsic aggregation‐caused quenching (ACQ) effects . To overcome this problem, many molecular strategies have been developed to alleviate the self‐quenching effect . In particular, we have demonstrated that bulky substituents can suppress the continuous packing of conjugated luminogens, which allows the preservation of luminescence efficiency .…”

“…To overcome this problem, many molecular strategies have been developed to alleviate the self‐quenching effect . In particular, we have demonstrated that bulky substituents can suppress the continuous packing of conjugated luminogens, which allows the preservation of luminescence efficiency . Nevertheless, the intrinsic contradiction of high solid‐state efficiency (avoiding aggregation) and mesophase formation (ordered molecular packing) is still difficult to solve fundamentally.…”

Crystal Structure and Molecular Packing Behavior of Poly(2,3-diphenyl-1,4-phenylenevinylene) Derivatives Containing Alkyl Side-Chains

“…To overcome this obstacle, a new family of soluble PPV, namely, poly(2,3-diphenylphenylenevinylene) (DP-PPV) and its derivatives were synthesized with the solid-state PL efficiency higher than 60%. 32,33 Recently, we have also reported various types of novel DP-PPV derivatives 34,35 and DP-PPVbased copolymers 36−38 which can render excellent polymer light emitting diode performance. Similar to other PPV-based polymers, the PL properties of DP-PPV derivatives are also strongly dependent on their assembly behavior.…”