Photofading of an Extended BOPHY Chromophore Dispersed in Poly(methyl methacrylate) as a Chemical Actinometer

Abstract

The target compound is a member of the symmetric pyrrole-BF 2 family, known as BOPHY, which has been equipped with 3,8styryl groups that push the absorption maximum to lower energy. To assist solubility and facile dispersion in plastic films, poly(ethylene glycol) chains are added to the styryl groups. The photophysical properties are somewhat sensitive to changes in solvent polarity and temperature due to the imposition of weak, intramolecular charge-transfer character. The chromophore bleaches under white-light illumination to form an intermediate species that absorbs and emits at higher energy. This species is believed to be a BOPHY unit with one styryl arm removed from the conjugation path. The intermediate is quite resistant to photobleaching but does fade on prolonged illumination. The kinetics associated with photobleaching in poly(methyl methacrylate) films allow development of a simple model that can be used to establish a robust chemical actinometer for recording exposure to sunlight. Similar photofading behaviour is observed in polar solution, where self-catalysis is observed, with the overall kinetics depending on the nature of the solvent.[a] O.

Recent advances in the synthesis of luminescent tetra-coordinated boron compounds

“…Various substituents linked to the framework of the bispyrrole-boron were studied. [197][198][199][200][201][202][203][204][205][206][207][208][209][210][211][212][213][214][215][216] Although, most of the studies reported a six-membered ring formation, in 2016, Shen and co-workers reported 197 both five and six membered ring formation using hydrazine-Schiff base linked bispyrrole. Compound 217 (six-membered-ring) showed efficient solidstate fluorescence owing to the weak intermolecular interactions and a large Stokes shift, whereas, compound 218 (fivemembered-ring) has a small Stokes shift which results in weak fluorescence in the solid-state via self-quenching.…”

Bio-Inspired Artificial Light-Harvesting Arrays Based on Boron(III)-Chelates

“…Additional work has described the photochemical bleaching of BOPHY in liquid and solid phases. It appears that the compound is highly resistant to photofading under visible light illumination [12].…”

Origin of Fluorescence from Boranils in the Crystalline Phase

“…Such materials can provide strong absorbance from relatively narrow layers and are therefore highly attractive for applications as light harvesters. A further advantage of crystalline samples stems from their likelihood to display resistance toward photobleaching, a process that often plagues simple organic dyes in aerobic media. , Consequently, ever-increasing interest is focusing on the identification of fluorophores that retain characteristic emission in the crystalline phase without formation of H- or J-aggregates. In essence, there is a need for solid-state fluorophores exhibiting either broad emission spectra, such materials being putative white-light emitters, or narrow spectral profiles that could be useful as fluorescent markers .…”