Structural and spectroscopic properties of the 1?1 complex of ?2, 2?-bis-1,3-dithiole (TTF) and 1,2,4,5-tetracyanobenzene (TCNB)

3 a,6 a-Diaza-1,4-Diphosphapentalenes: Synthesis and Complexation with the Organic π-Acceptor 1,2,4,5-Tetracyanobenzene

The reaction of PCl₃ with diethyl ketazine and 4-phenylcyclohexanone azine results in the formation of 1,4-dichloro-3a,6a-diaza-1,4-diphosphapentalenes which were reduced by magnesium in THF to give corresponding diazadiphosphapentalenes EtMeDDP and PhcHexDDP, containing two-coordinate phosphorus atoms. According to the CVA data, the new diazadiphosphapentalenes are strong electron donors showing oxidation peak potentials at 0.34 and 0.10 V, respectively, (vs. Ag/AgCl). Interaction of 1,2,4,5-tetracyanobenzene (TCNB) with the obtained diazadiphosphapentalenes in any stoichiometry produces sandwich complexes of the composition DDP-TCNB-DDP. Black-purple crystals of π-complexes contain infinite molecular chains with short P⋅⋅⋅P contacts between DDP molecules and short (Csp² -H⋅⋅⋅N) contacts between TCNB molecules. Calculations showed that each TCNB molecule is an acceptor of ∼0.3e from two DDP molecules. Estimation of the HOMO-LUMO gap from the onset of optical absorption give values of 1.25 eV and 1.31 eV for [(EtMeDDP)₂ (TCNB)] and [(PhcHexDDP)₂ (TCNB)] respectively.

Deepening Insights of Charge Transfer and Photophysics in a Novel Donor-Acceptor Cocrystal for Waveguide Couplers and Photonic Logic Computation

The charge transfer and photophysics in a new light-emitting cocrystal with ribbon-like morphology are revealed in-depth. These cocrystals can serve as an efficient 1D optical waveguide, and the cocrystal waveguide couplers fabricated by a probe-assisted crystal-moving technique exhibit interfacial white emission and can function as basic photonic logic gates, showing potential for future integrated photonics.

Rational Design of Charge-Transfer Interactions in Halogen-Bonded Co-crystals toward Versatile Solid-State Optoelectronics

Charge-transfer (CT) interactions between donor (D) and acceptor (A) groups, as well as CT exciton dynamics, play important roles in optoelectronic devices, such as organic solar cells, photodetectors, and light-emitting sources, which are not yet well understood. In this contribution, the self-assembly behavior, molecular stacking structure, CT interactions, density functional theory (DFT) calculations, and corresponding physicochemical properties of two similar halogen-bonded co-crystals are comprehensively investigated and compared, to construct an "assembly-structure-CT-property" relationship. Bpe-IFB wire-like crystals (where Bpe = 1,2-bis(4-pyridyl)ethylene and IFB = 1,3,5-trifluoro-2,4,6-triiodobenzene), packed in a segregated stacking form with CT ground and excited states, are measured to be quasi-one-dimensional (1D) semiconductors and show strong violet-blue photoluminescence (PL) from the lowest CT1 excitons (ΦPL = 26.1%), which can be confined and propagate oppositely along the 1D axial direction. In comparison, Bpe-F4DIB block-like crystals (F4DIB = 1,4-diiodotetrafluorobenzene), packed in a mixed stacking form without CT interactions, are determined to be insulators and exhibit unique white light emission and two-dimensional optical waveguide property. Surprisingly, it seems that the intrinsic spectroscopic states of Bpe and F4DIB do not change after co-crystallization, which is also confirmed by theoretical calculations, thus offering a new design principle for white light emitting materials. More importantly, we show that the CT interactions in co-crystals are related to their molecular packing and can be triggered or suppressed by crystal engineering, which eventually leads to distinct optoelectronic properties. These results help us to rationally control the CT interactions in organic D-A systems by tuning the molecular stacking, toward the development of a fantastic "optoelectronic world".