Aggregation‐Induced Emission Leading to White Light Emission in Diphenylbenzofulvene Derivatives

Abstract

The search for a unique molecular system able to efficiently emit in the total visible range of the electromagnetic spectra, i. e., white light emission (WLE), is a topic of intense research. We here show that aggregates formed by diphenylbenzofulvene (DPBF) derivatives are from two to four orders of magnitude more emissive than their monomers. From a simple strategy, involving structural modification of a DPBF propelled shape core, a close match with the pure white light emission coordinates is obtained with a combination of two derivatives in films, with featured solid‐state emission, without involvement of D−A groups or energy transfer processes.

Practical Design of 3,6-Di-tert-butyldiphenyldibenzofulvene Derivatives with Enhanced Aggregation-Induced Emission

“…In Figure 2, the absorption spectra of the compounds in acetonitrile and MeCN/water mixtures, for the water fraction in which the compound has its highest fluorescence quantum yield (ϕ F ), clearly show the difference indicative of the formation of aggregates in the water content mixtures (Figure 3). As found for other DPBF derivatives, 3,17,18 the increase in f w , and consequently the change from a good to a poor solvent medium, leads to a change in 3,6-dtb-DPBF from an isolated molecule to an emissive aggregate. Data in Figure 3 (summarized in Table 1) show that the compounds are poorly emissive in acetonitrile, becoming emissive when f w ≥ 60%, with maximum fluorescence emission efficiency (ϕ F in Table 1) at f w values of 75% (3,6-dtb-DPBF), 60% (3,6-dtb-DPBFMe), and 80% for [3,6-dtb-DPBF(Me) 2 ] (Figure 3).…”

“…The complete set of electronic spectral data (including wavelength maxima for absorption, fluorescence emission, fluorescence quantum yields, ϕ F , and Stokes shifts, Δ SS ) is summarized in Table . Literature data for the nonsubstituted diphenyldibenzofulvene (DPBF) is also included for comparison …”

“…In most of the emissive aromatic type systems, aggregation introduces π–π interactions that quench solid-state emissions, leading to the prevalent phenomenon (in the solid state) of aggregation-caused quenching (ACQ). In contrast with this phenomenon, aggregation-induced emission (AIE) is a phenomenon coined by Tang and co-workers in 2001 that reflects the large increase in the luminescence efficiency in solution of a bad solvent (aggregate), in comparison with a good solvent (dissolved monomer emission). , Whereas in its early days the molecules displaying this effect (AIEgens) included the core structures hexaphenylsilole (HPS), tetraphenylethylene (TPE), and phenothiazine (PTZ), today it has matured and has expanded to many other families of molecules and polymers and, more recently, to diphenyldibenzofulvene derivatives (DPBFs). − …”

Aggregation-Induced Emission with Alkynylcoumarin Dinuclear Gold(I) Complexes: Photophysical, Dynamic Light Scattering, and Time-Dependent Density Functional Theory Studies

“…Since the pioneering study of Tang and co-workers, there has been a substantial increase in the number of luminescent compounds with aggregation-induced emission (AIE) properties (AIEgens). − One current strategy to improve the luminescence emission in the solid state involves the development of structures, whereby when molecular movements, free motion, or internal rotation (loose bolt or rigid rotor effects) of a molecule are restricted, the radiative deactivation increases because of a decrease of the radiatiotionless deactivation channel . This is valid for excited singlet and triplet states. − AIEgens, such as tetraphenylethylene (TPE), show weak emissions in dilute solutions (good solvents) but emit intensely when they aggregate and, usually, also in the solid state (aggregates).…”

“…This is valid for excited singlet and triplet states. − AIEgens, such as tetraphenylethylene (TPE), show weak emissions in dilute solutions (good solvents) but emit intensely when they aggregate and, usually, also in the solid state (aggregates). The AIE effect has been linked to the restriction in intramolecular rotations, by aggregate formation, of the emissive molecules, which efficiently limits the radiationless energy deactivation, enhancing the radiative decay. , With AIEgens, the particular shape of the TPE units prevents luminogens from packing (in the luminescence loss π–π stacking), while the intramolecular rotations (an efficient route for radiationless deactivation through the loose bolt effect) are physically constrained in the condensed phase. Aggregates typically have dimensions around 100 nm, and its luminescence efficiency is also found to depend on the degree of crystallinity.…”