Excimer Formation of Perylene Bisimide Dyes within Stacking-Restrained Folda-Dimers: Insight into Anomalous Temperature Responsive Dual Fluorescence

Abstract

By tethering two PBI moieties to the ortho-carbon positions of a carborane unit, we are able to build up a new PBI folda-dimer (BPBI-CB-1). The synthesized compound adopts different configurations in different solvents with dual emissions as its characteristic. The two PBI moieties in the molecule are either appearing in a weakly interacted, monomer-like state or brought in close π-π contact to each other, forming an interacted stacking state. The equilibrium between these two states is governed by the nature of solvents and testing temperature.Spectroscopic and theoretical studies conclude that dual emission bands originate from intramolecular monomer-like and stacking states, respectively. Remarkably, in certain solvent such as 1,2-dichloroethane, both emission intensities increase with raising temperature. The positive temperature response of the monomer emission is ascribed to increased amount of monomer-like population owing to its endothermic energy state, while for the excimer emission it is rationalized by the increase of the population in bright exciton state, resulting in an increase of emission yield that compensates the decrease of the population of the stacking state. To our knowledge, this is the first report on positive temperature responsive dual emissions associated with the synergism of intramolecular inter-subunit aggregation/dissociation and excimer transformation.

Resonance-Enhanced Two-Photon Absorption and Optical Power Limiting Properties of Three-Dimensional Perylene Bisimide Derivatives

“…This enhancement should be ascribed to the cooperative stereo effect induced by the CB blocks. In another respect, the two PBI units in PCB-PBI were calculated to be ∼14 Å apart, from center to center, and the angle between them was ∼60°, which ultimately ruled out the possible aggregation of an intramolecular intra-PBI subunit . Considering that the order of normalized δ 2PA magnitude is PCP-PBI > NCP-PBI > CB-PBI (1/2) > R-PBI, we can conclude the extensive contribution of the ICT process from the aromatic units to the electron-withdrawing CB blocks.…”

“…In another respect, the two PBI units in PCB-PBI were calculated to be ∼14 Å apart, from center to center, and the angle between them was ∼60°, which ultimately ruled out the possible aggregation of an intramolecular intra-PBI subunit. 23 Considering that the order of normalized δ 2PA magnitude is PCP-PBI > NCP-PBI > CB-PBI (1/2) > R-PBI, we can conclude the extensive contribution of the ICT process from the aromatic units to the electronwithdrawing CB blocks. Taken together, the results highlight the importance of stereo effect and ICT efficiency in designing efficient 2PA materials.…”

“…In this case, the distortion effect can be uniquely compensated by the conjugated electron-donating substituents . Due to the tendency for π–π interaction, PBIs are prone to form self-organized aggregates like H-type columnar aggregates, J-aggregate formation, or possible slip-stacked packing. − As a universal strategy, the formation tendency of electronically decoupled aggregates can be reduced by nonplanar substituents. Different from the structural modifications at bay positions with decreased conjugation and twisted planarity, introduction of a rigid and sphere structural o -carborane ( o -CB) unit is an effective way to screen aggregation of PBI units owing to steric hindrance. , Meanwhile, o -CB units with electron-deficient characteristics of skeletal electrons and highly polarizable σ-aromatic character can conjugate to aryl units through the C–C bond directly. ,− Chujo and co-workers observed the bright intramolecular charge transfer (ICT) process via the σ*−π* conjugation through robust electronic conjugation in the system of multifunctional o -CB–pyrene dyads.…”

An O-Carborane Derivative of Perylene Bisimide-Based Thin Film Displaying both Electrochromic and Electrofluorochromic Properties

“…As reported earlier, the carborane units have been generally introduced to modulate the stereo-structures of PBI derivatives for blocking the dense stacking of the PBI units aiming to maintain their highly efficient fluorescence emission property when they are in a solid or film state. In addition, the non-planar structures are favorable for solvation, and thereby modification with carborane units has been taken as a strategy to increase the solubility of the relevant compounds in common solvents. − This phenomenon was commonly used to improve the films′ sensing performances. Unlike chemical sensing, for film-based EC and EFC processes, both mass transfer and electron transport are crucial, as in liquids, electricity conduction is realized through ion migration, but in solids, the conduction is a result of electron transport.…”

“…To verify the statement, a non-planar perylene bisimide-carborane derivative (PBI-CB, Figure a) was employed to perform the examination. PBI-CB was chosen as it possesses a unique non-planar structure enabling good solubility in common organic solvents and allowing efficient film fabrication. , Photoelectrochemical studies revealed that the compound-based, specially prepared films depicted not only remarkable EC but also fascinating EFC properties. This paper reports the details.…”