Cs -Symmetric, Peripherally Fluorinated Boron Subphthalocyanine–Subnaphthalocyanine Hybrids: Shedding New Light on Their Fundamental Photophysical Properties and Their Functionality as Optoelectronic Materials

• Published in: Journal of physical chemistry. C Vol. 127; no. 1; pp. 702 - 727
• Main Authors: Farac, Nina F., Tetreault, Adam R., Bender, Timothy P.
• Format: Journal Article
• Language: English
• Published: American Chemical Society 12.01.2023
• Subjects: C: Physical Properties of Materials and Interfaces
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.2c07276

Hybridization of boron subphthalocyanine (BsubPc) and boron subnaphthalocyanine (BsubNc) has been modestly explored in the past, and was therefore carried out herein to access a subclass of these chromophores denoted as Ra-F x Bsub­(Pc3–p -Nc p ) hybrids, where Ra is the axial halide substituent (axial chloride, Cl-, or axial fluoride, F-), x = 8, and p = 1. These chromophores were targeted as new candidate materials for organic electronic applications due to their Cs symmetry, in-plane dipole moment, and unique photophysical properties. Cl-/F- F8Bsub­(Pc2-Nc1) hybrids were compared to Cl-/F- F8BsubPc hybrids, which are analogous compounds with an identical number of peripheral fluorine atoms but lower degree of π-conjugation. Upon photoexcitation of dilute toluene solutions and doped thin films with polystyrene as a nonemissive host, F8Bsub­(Pc2-Nc1) hybrids exhibited distinctively broad absorption spectra and narrow emission profiles with red-shifted peak photoluminescence wavelengths in the 618–623 nm region compared to F8BsubPc hybrids (581–584 nm). Electroluminescence properties were probed in simple solution-cast organic light-emitting diodes (OLEDs) in which all four hybrids were diluted within an F8BT emissive polymer host. Upon electronic excitation, electroluminescence (EL) of Cs -symmetric hybrids followed the same trends as photoluminescence (PL), with OLED devices displaying narrow EL in the orange region (588–592 nm) for F8BsubPc hybrids and in the near-red region for F8Bsub­(Pc2-Nc1) hybrids (627–632 nm). The photophysical processes important to OLEDs moderately improved with less π-conjugation in the periphery of the Cs -symmetric hybrids [F8Bsub­(Pc2-Nc1) vs F8BsubPc; EQEMax: 0.099% vs 0.129%; luminance: 500 cd/m2 vs 1000 cd/m2 at maximum current density; relative PL quantum yields (QYs) ≈ 17–22% vs ≈ 35–44%]. Electrochemical data showed that Cs symmetry introduces reversibility or quasi-reversibility in the oxidation regime at potentials >1 V, and peripheral fluorination enables reversibility in the reduction process. Overall, F8Bsub­(Pc2-Nc1) hybrids embody several unique physical characteristics into one: broad absorption spectra (full width at half-maximum height, FWHMsol abs = 53–55 nm, FWHMfilm abs = 71 nm), narrow near-red electroluminescence (FWHMOLED EL = 33 nm), and photoluminescence (FWHMsol PL = 25–26 nm, FWHMfilm PL = 32 nm) emission, small energy band gaps (1.95–1.96 eV), high extinction coefficients (ε ≈ (5.65–6.16) × 104 M–1 cm–1), and dual electrochemical versatility. These results provide new physical insights into the material properties of Cs -symmetric macrocycles and advance the consideration of F8Bsub­(Pc2-Nc1) and F8BsubPc hybrids for optoelectronic applications.