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International audience; Luminescent exciplexes based on a chiral electron donor and achiral acceptors are reported as a new approach to design circularly polarized (CP) and thermally activated delayed fluorescence (TADF) emitters. This strategy results in rather high CP luminescence (CPL) values with g$_{lum}$ up to 7x10$^{-3}$, one order of magnitude higher in comparison to the CPL signal recorded for the chiral donor alone g$_{lum}$ similar to 7x10$^{-4}$. This increase occurs concomitantly with a CPL sign inversion, as a result of the strong charge-transfer emission character, as experimentally and theoretically rationalized by using a covalent chiral donor-acceptor model. Interestingly, blue, green-yellow and red chiral luminescent exciplexes can be obtained by modifying with the electron accepting character of the achiral unit while keeping the same chiral donor unit. These results bring new (inter)molecular guidelines to obtain simply and efficiently multi-color CP-TADF emitters.

Mechanochromic luminescent materials have attracted much attention and present a variety of applications in information security, data recording, and storage devices. However, most of these smart luminescent systems are based on typical fluorescence and/or phosphorescence mechanisms; the mechanochromic delayed fluorescence (MCDF) materials involving switching singlet and triplet states are rarely studied to date. Herein, new 2D layered metal–organic micro/nanosheets, [Cd(9‐AC)2(BIM)2] (named as MCDF‐1; 9‐AC = anthracene‐9‐carboxylate and BIM = benzimidazole) and its solvate form containing interlayer CH3CN (named as MCDF‐2), which exhibit reversible mechanochromic delayed fluorescence characteristics, are presented. With applying the mechanical force, the luminescent center of MCDF‐1 can be converted from 9‐AC/BIM exciplex to 9‐AC/9‐AC excimer, resulting in alternations of delayed fluorescence. Such luminescent change can be further recovered by CH3CN fumigation, accompanied by the structural transformation from MCDF‐1 to MCDF‐2. Furthermore, the force‐responsive process also refers to the energy redistribution between singlet and triplet states as inferred by both temperature‐dependent photophysics and theoretical calculations. Therefore, this work not only develops new 2D micro/nanosheets as MCDF materials, but also supplies a singlet–triplet energy switching mechanism on their reversible mechanochromic process.

We report a successful observation of the electro-photoluminescence (EL-PL) in thin, exciplex emitting, organic, solid films. The increasing electric field applied to injecting electrodes tends to reduce the total light emission because of the dissociation of emissive exciplex states and their precursors, and, at the same time, the radiative recombination of injected holes and electrons enhances the output of the electroluminescence (EL), the process that suppresses the total luminescence quenching. Increasing bulk concentration of the charge leads the EL output to exceed the PL component, a negative quenching (enhancement of the total emission) is observed.

Charge-transfer interactions of singlet excited trans isomers of n-styrylnaphthalene (n-StN, with n = 1 and 2), 9-styrylanthracene (9-StAn), and n-styrylphenanthrene (n-StPh, with n = 1, 2, and 9) with electron donors (N,N-diethylaniline, DEA, and 4-bromo-N,N-dimethylaniline, BrDMA) and acceptors (p-dicyanobenzene, DCNB) were studied in polar and nonpolar solvent at room temperature by absorption picosecond laser flash photolysis. The transient absorption formed within the laser pulse, already attributed to S1 → Sn and S2 → Sn transitions, were replaced, in the presence of amine quenchers, by the absorption of the exciplex (nonpolar solvent) or of contact radical ion pairs (CRIP, polar solvent). The time evolution of these transients showed the formation of the solvent-separated radical ion pair (SSRIP) and then of the longer-lived absorption of triplet state and/or radical anions. In the presence of DCNB in polar solvent the evolution of the first excited singlet showed the formation of CRIP, SSRIP, and ...