Restriction of intramolecular motion (RIM) is commonly adopted to achieve high luminescence for aggregation-induced emission (AIE) materials. However, recent studies found that RIM cannot fully explain the behavior of some new systems because of the existence of extra nonradiative excited state channels. In this work, two D-π-A type molecules, TPA-P-C and CBZ-P-C with AIE properties, were prepared via the Suzuki− Miyaura reaction. CBZ-P-C showed an unusual solvent effect, being nonemissive in low-polar solvents but highly emissive in polar solvents. Theoretical calculations and time-resolved spectroscopic experiments demonstrated for CBZ-P-C a quantitative intersystem crossing (ISC) in low-polar solvents, resulting in low emission quantum yield but high singlet oxygen generation. In addition, a rigid matrix (triphenylphosphine (TPP)) was selected as host for the stabilization of the triplet excitons. Both doping materials showed high room-temperature phosphorescence (RTP) as a consequence of the highly efficient triplet exciton generation. The present study provides a new insight for understanding AIE materials and paves an easy yet efficient way for the excited-state modulation of AIE molecules.

New multimodular donor–acceptor chromophores combining phenothiazine (D′), benzothiadiazole (A), and diphenylamine/carbazole (D) units in complex configurations (D−π–A−π–D′−π–A−π–D and D–A−π–D′−π–A–D) were designed, synthesized, and investigated for their peculiar intramolecular charge transfer (ICT) behavior. In these organic materials, the modification of the end–capping donor units and the extension of π-conjugation are key factors in tuning their optical, photophysical and electrochemical properties, as revealed by the density functional theory calculations, ultrafast spectroscopy experiments and cyclic voltammetry measurements. The femtosecond transient absorption and broadband fluorescence up-conversion results surprisingly show two distinct ICT processes. The first ICT is assigned to the charge displacement from the lateral donors to the acceptors and the second ICT (ICT′) to the electron donation from the central phenothiazine. The detection of two ICT states accounts for the peculiar dual emission observed for these molecules. In addition, large two-photon absorption cross sections were revealed for these symmetrical and quadrupolar chromophores. These features make the investigated molecules appealing as new organic materials for possible light-to-energy conversion applications.

A series of 3,7-bis(arylethynyl)-substituted phenothiazine-based fluorophores (bearing benzene, naphthalene, methoxynaphthalene, anthracene, phenanthrene, and pyrene) were designed and synthesized via a Pd-catalyzed Sonogashira cross-coupling reaction. These molecules show in solution large Stokes shifts (generally 5500−6500 cm −1 ) and high quantum yields (40−82% depending on the aryl groups), as a consequence of the planarization of their butterfly-like structure occurring in the excited state. Moreover, significant two-photon absorption was revealed for these phenothiazine derivatives, whose cross section increases upon enhancing the molecular conjugation. The remarkable Stokes shifts, fluorescence quantum yields, and twophoton absorption make these molecules appealing as fluorescent probes for bioimaging applications. Significant emission was also detected in the solid state where anthracene-, phenanthrene-, and pyrene-substituted phenothiazines show red-shifted emission maxima compared to the solution, indicating considerable π−π staking. The anthracene-substituted phenothiazine arouses particular interest, as it exhibits photoinduced intramolecular charge transfer (ICT) from the phenothiazine to the anthracene, revealed by its important fluorosolvatochromism and through ultrafast transient absorption experiments. The spectroscopic results are in line with the time-dependent density functional theory (TD-DFT) calculations and cyclic voltammetry measurements. The anthracene-substituted molecule also features a remarkable triplet production and hints of a delayed fluorescence behavior, allowed in nonpolar solvents by a fairly competitive reverse intersystem crossing pathway. These findings make the investigated molecules interesting as new organic active materials for optoelectronic devices.