Phosphorescence Tuning through Heavy Atom Placement in Unsymmetrical Difluoroboron β‐Diketonate Materials

Abstract

Difluoroboron β-diketonates (BF bdks) show both fluorescence (F) and room-temperature phosphorescence (RTP) when confined to a rigid matrix, such as poly(lactic acid). These materials have been utilized as optical oxygen sensors (e.g., in tumors, wounds, and cells). Spectral features include charge transfer (CT) from the major aromatic donor to the dioxaborine acceptor. A series of naphthyl-phenyl dyes (BF nbm) (1-6) were prepared to test heavy-atom placement effects. The BF nbm dye (1) was substituted with Br on naphthyl (2), phenyl (3), or both rings (4) to tailor the fluorescence/phosphorescence ratio and RTP lifetime-important features for designing O sensing dyes by means of the heavy atom effect. Computational studies identify the naphthyl ring as the major donor. Thus, Br substitution on the naphthyl ring produced greater effects on the optical properties, such as increased RTP intensity and decreased RTP lifetime compared to phenyl substitution. However, for electron-donating piperidyl-phenyl dyes (5), the phenyl aromatic is the major donor. As a result, Br substitution on the naphthyl ring (6) did not alter the optical properties significantly. Experimental data and computational modeling show the importance of Br position. The S and T states are described by two singly occupied MOs (SOMOs). When both of these SOMOs have substantial amplitude on the heavy atom, passage from S to T and emission from T to S are both favored. This shortens the excited-state lifetimes and enhances phosphorescence.

Meta‐Dimethoxy‐Substituted Difluoroboron Dibenzoylmethane Poly(Lactic Acid) Nanoparticles for Luminescence Anisotropy

“…The P1 and P2 nanoparticles showed unusually strong RTP for metal‐free phosphors. Typically with BF 2 bdk materials, heavy atoms are introduced as substituents on the arene rings of the dye to increase RTP intensity relative to fluorescence . However, this ICT scaffold, with enhanced phosphorescence, shows progress toward eliminating the heavy atom altogether for oxygen‐sensing boron dyes.…”

Methoxy‐Substituted Difluoroboron Benzoylacetonate Complexes with Color‐Tunable Phosphorescence

“…Also, diaryl systems with extended π‐conjugation often result in overlapping singlet and triplet emission . This can complicate analysis of optical properties and competing effects, such as charge transfer (CT), π‐conjugation and intersystem crossing (ISC) to the triplet state . To simplify analysis, we explore a model consisting of a single aromatic unit to better understand the role of methoxy substitution, both number and position, on the dye scaffold.…”

Full-type photoluminescence from a single organic molecule for multi-signal temperature sensing

“…Compared to short-lived fluorescence, persistent phosphorescence (PP) has attracted increasing attention due to its large Stokes shift and long lifetime. [14][15][16][17][18][19][20][21] However, compared to inorganic counterparts, organic phosphors generally show a relatively short phosphorescence lifetime (o10 ms) at room temperature due to rapid non-radiative decay of triplet excitons. [22][23][24][25][26][27][28][29] To stabilize the triplet excitons, various strategies including crystallization, host-guest inclusion, H-aggregation, and doping in a rigid matrix have been used to achieve efficient RTP in organic materials.…”