Heavier pnictogens - treasures for optical electronic and reactivity tuning

Phospha-cyanines in Their Ideal Polymethine State: Synthesis and Structure-Property Relationships

We report the synthesis and full characterization of a family of phosphorus-containing polymethine cyanines (phospha-cyanines). The compounds are easily prepared in two steps, starting from readily available phosphanes. The impact of the P-substituents and the counterions on the structural and optical properties is investigated through a joint experimental/theoretical approach. Based on the study of the single-crystal X-ray diffraction structures, all phospha-cyanines present a bond length alternation close to zero, independently of the substituents and counterions, which indicates an ideal polymethine state. All these compounds display the typical cyanine-like UV-vis absorption with an intense and sharp transition with a vibronic shoulder despite possessing a reverse electronic configuration compared to "classical" cyanines. Time-dependent density-functional theory calculations allowed us to fully rationalize the optical properties (absorption/emission wavelengths, luminescence quantum yields). Interestingly, due to the tetrahedral shape of the P atom, the optical properties are independent of the counterion, which is in marked contrast with N-analogues, which enables predictive engineering of the phospha-cyanines regardless of the medium in which they are used.

Synthesis and Photophysical Properties of Heavier Pnictogen Complexes

Recent success in the synthesis of π-conjugated heavier pnictogen (As, Sb, and Bi) compounds and their transition metal complexes has led to the current surge in interest that led to significant development in the field of photophysical and optoelectronic properties of heavier pnictogens and their transition metal complexes. The presence of heavier pnictogens (As, Sb and Bi) in the molecular skeleton promotes inter-system crossing (ISC) and reverse inter-system crossing (RISC), because of the heavy atom effect, via altering the intermolecular interactions and orbital energy levels. As a result, π-conjugated heavier pnictogen compounds such as arsines, dibenzoarsepins, arsinoquinoline, heterofluorene, benzo[b]heterole (heterole=arsole, bismole, and stibole) show unique optoelectronic properties such as narrow bandgap, low-energy absorption, and long-wavelength emission than lighter pnictogen-based compounds. This review focuses on recent advances in the synthesis and photophysical properties of heavier pnictogen compounds. The synthesis and photophysical properties of heavier pnictogens are discussed and elaborated.

4-Aryldithieno[3,2-b:2',3'-d]arsoles: effects of the As-substituent on the structure, photophysical properties, and stability

Dithieno[3,2-b:2',3'-d]arsole (DTA) is one of the representative arsenic-containing conjugated units. In this work, the effects of the As-substituent on the structure, photophysical properties, and stability were investigated. Surprisingly, the As-substituent affected the structural relaxation and stability in the photo-excited state, while there was negligible effect in the ground state. Bulky substituents resulted in red-shifted emissions due to the relaxation of steric repulsion upon photo-excitation. In addition, the crystal structure highly affected the photo-degradation behaviors.

Systematic Study of Pnictogen-Fused Heterofluorenes

Heteroatom-fused π-conjugated molecules have attracted considerable attention, and various elements for such fusion have been investigated. Herein, we focused on pnictogen-fused heterofluorenes. The structures, reactivity with O₂ and I₂, coordination ability to AuCl, and photophysical properties were systematically studied to better understand the effects of pnictogen atoms on the nature of π-conjugated molecules.

Golden Age of Fluorenylidene Phosphaalkenes-Synthesis, Structures, and Optical Properties of Heteroaromatic Derivatives and Their Gold Complexes

The substitution of 2,7-dibromo-9-fluorenyl phosphaalkenes with heteroaromatic substituents (bithiophene, benzothiophene, pyridine) offers access to interesting push–pull dye molecules. Steric shielding due to the bulky P-substituent gives marked different reactivities at the 2- and 7-positions, allowing the synthesis of mixed/asymmetric derivatives. Further functionalization via gold(I) coordination was demonstrated and increased the acceptor character, concomitant with a red-shifted absorption.

Tweaking the Charge Transfer: Bonding Analysis of Bismuth(III) Complexes with a Flexidentate Phosphane Ligand

To account for the charge transfer and covalent character in bonding between P and Bi centers, the electronic structures of [P(C₆H₄-o-CH₂SCH₃)₃BiCl_n]^(3–n)+ (n = 0–3) model species have been investigated computationally. On the basis of this survey a synthetic target compound with a dative P→Bi bond has been selected. Consecutively, the highly reactive bismuth cage [P(C₆H₄-o-CH₂SCH₃)₃Bi]³⁺ has been accessed experimentally and characterized. Importantly, our experiments (single-crystal X-ray diffraction and solid-state NMR spectroscopy) and computations (NBO and AIM analysis) reveal that the P···Bi bonding in this trication can be described as a dative bond. Here we have shown that our accordion-like molecular framework allows for tuning of the interaction between P and Bi centers.

The bonding situation in species with the general formula of [P(C₆H₄-o-CH₂SCH₃)₃BiCl_n]⁽³⁻ⁿ⁾⁺ (n = 0−3) has been investigated computationally, and on this basis a selected example has been accessed synthetically. The structural and solid-state NMR studies reveal that the weak secondary pnictogen interaction in P(C₆H₄-o-CH₂SCH₃)₃BiCl₃ can be tuned into dative bonding by enhancing the charge transfer from the phosphorus to the bismuth center, which is accompanied by a change in the spin−spin coupling mechanism between the ³¹P and ²⁰⁹Bi nuclei.

A Modular Approach to Phosphorescent π-Extended Heteroacenes

A modular route to previously inaccessible classes of ring-fused π-extended heteroacenes bearing the heavy inorganic element tellurium (Te) is presented. These new materials can be viewed as n-doped analogs of molecular graphene subunits that exhibit color tunable visible light phosphorescence in the solid state and in the presence of air. The general mechanism of phosphorescence in these systems was probed experimentally and computationally via time-dependent density functional theory (TD-DFT). The incorporation of Te into π-extended oligoacene frameworks was achieved by an efficient Zr/Te transmetalation protocol; related zirconium-element exchange reactions have been used to prepare both electron-rich and electron-deficient heterocycles containing different elements from throughout the p-block. Therefore, the current study provides a clear path to incorporate inorganic elements into heteroacenes of greater complexity and side group selectivity compared to existing synthetic routes.