Aromatic Difluoroboron β-Diketonate Complexes: Effects of π-Conjugation and Media on Optical Properties

Abstract

Aromatic difluoroboron β-diketonate complexes (BF2bdks) are classic fluorescent molecules that have been explored as photochemical reagents, two-photon dyes, and oxygen sensors. To gain a better understanding of their emissive properties in both solution and polymer matrices, BF2bdks with varying aromatic groups were synthesized and their photophysical properties were investigated in both methylene chloride and poly(lactic acid) (PLA). Absorption spectra showed systematic variations that are well correlated with structural features, including the size of the aryl substituent and the presence of a para electron donating methoxy substituent. Computational modeling of the absorption spectra with the TD-B3LYP/6-311+G(d)//B3LYP/6-31G(d) formulation of density functional theory and a polarizable continuum model of dichloromethane solvent shows that all systems show intense π–π* one-electron excitations, usually from one of the highest occupied MOs (HOMO-k, k=0, 1, 2) to the lowest unoccupied MO (LUMO). Emission properties are sensitive to the dye structure and medium. Based on spectroscopic and lifetime studies, BF2bdks exhibit comparable fluorescence properties in both solutions and polymers when the diketonate group is functionalized with smaller aromatic ring systems such as benzene. For BF2bdks with larger arene ring systems, such as anthracene, emission from a strong intramolecular charge-transfer (ICT) state was also noted in both solution and in PLA. There are differences in relative intensities of peaks arising from π-π* and ICT excitations depending upon dye loading in PLA. Substituent effects were also observed. Electron-donating methoxyl groups on the aromatic rings lead to enhanced fluorescence quantum yields. For certain dyes, phosphorescence is detected at low temperature or under a nitrogen atmosphere in PLA matrices.

Influence of Substituent and Benzoannulation on Photophysical Properties of 1-Benzoylmethyleneisoquinoline Difluoroborates

“…This solvent is known to prevent boron-ligand dissociation, exciplex formation, or photochemical reactions possible in solvents containing Lewis bases, aromatic rings, or double bonds. 53 Moreover, the self-aggregation is not preferred in dilute solutions as it has already been demonstrated for quinoline derivatives. 49 Figure 1 shows the absorption spectra of 1-8 and corresponding values are presented in Table 1.…”

Recent progress of optical functional nanomaterials based on organoboron complexes with β-diketonate, ketoiminate and diiminate

“…Various types of asymmetric complexes and tunable emissions have been reported. [24][25][26][27][28][29][30][31][32][33][34] Emission colors can be modulated both in the solution and in solid states. In addition, a photo-responsive ketoiminate was obtained using a dithienylethene unit.…”

Difluoroboranyl derivatives as efficient panchromatic photoinitiators in radical polymerization reactions

“…Another examples are b-diketonate (OBF 2 O) and b-ketoiminate (NBF 2 O) difluoroboranyls [13]. Their easy functionalization makes the dyes very attractive as immobilized [13] probes or indicators [2,14], as dyes for biolabelling [15], chemodosimeters [16]. They also are used in solar cells applications [17].…”