Synthesis and Photophysical Properties of Heavier Pnictogen Complexes

Abstract

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.

Effects of Heavy p‐Block Elements on Photophysical Properties of π‐Conjugated Complexes and Organoelement Compounds

“…Many attempts have been conducted to clarify the element-dependent effects on the optical properties especially in π-conjugated systems. [129][130][131][132][133] Pyridine has the chemical structure in which one of the carbons of benzene is replaced by nitrogen, and the lone pair on nitrogen can act as a ligand because it does not participate in the aromatic 6π-electron system. In contrast, the lone pair of pyrrole, which has the chemical structure of cyclopentadiene with the saturated carbon replaced by nitrogen, has a weak coordination ability because it is involved in the aromatic 6π-electron system.…”

“…[157] Numerous compounds including group 15 elements have been synthesized based on the heterole skeletons. [133] For example, substitution of heavy elements in heterole resulted in the red shift of the absorption band and strong luminescence in the visible region (62NÀ As). [158,159] Since the lone pair of arsine has larger s-character than those of nitrogen and phosphorus, the trivalent arsenic atom has a trigonal pyramidal structure, which is different from trigonal planar pyrrole.…”

“…Nitrogen (N) usually forms the trivalent state, while the elements in the higher periods, such as phosphorus (P)‐bismuth (Bi), can be readily oxidized and subsequently form stable pentavalent states in addition to the stable trivalent states. Many attempts have been conducted to clarify the element‐dependent effects on the optical properties especially in π‐conjugated systems [129–133] . Pyridine has the chemical structure in which one of the carbons of benzene is replaced by nitrogen, and the lone pair on nitrogen can act as a ligand because it does not participate in the aromatic 6π‐electron system.…”

“…Numerous compounds including group 15 elements have been synthesized based on the heterole skeletons [133] . For example, substitution of heavy elements in heterole resulted in the red shift of the absorption band and strong luminescence in the visible region ( 62N−As ) [158,159] .…”