Photoluminescence in Carborane–Stilbene Triads: A Structural, Spectroscopic, and Computational Study

Abstract

A set of triads in which o- and m-carborane clusters are bonded to two stilbene units through Ccluster -CH2 bonds was synthesized, and their structures were confirmed by X-ray diffraction. A study on the influence of the o- and m- isomers on the absorption and photoluminescence properties of the stilbene units in solution revealed no charge-transfer contributions in the lowest excited state, as confirmed by (TD)DFT calculations. The presence of one or two B-I groups in m-carborane derivatives does not affect the emission properties of the stilbenes in solution, probably due to the rather large distance between the iodo substituents and the fluorophore. Nevertheless, a significant redshift of the photoluminescence (PL) emission maximum in the solid state (thin films and powder samples) compared to solution was observed; this can be traced back to PL sensitization, most probably due to more densely packed stilbene moieties. Remarkably, the PL absolute quantum yields of powder samples are significantly higher than those in solution, and this was attributed to the restricted environment and the aforementioned sensitization. Thus, the bonding of the carborane clusters to two stilbene units preserves their PL behavior in solution, but produces significant changes in the solid state. Furthermore, iodinated species can be considered to be promising precursors for theranostic agents in which both imaging and therapeutic functions could possibly be combined.

Improvement of Solid‐State Excimer Emission of the Aryl–Ethynyl‐o‐Carborane Skeleton by Acridine Introduction

“…Except for these materials, wide variety of solid‐state luminescent o ‐carboranes have been recently discovered. Thus, it can be said that o ‐carborane should be a versatile platform for designing advanced optoelectronic materials , , …”

Photoluminescence in m-carborane–anthracene triads: a combined experimental and computational study

“…But more interestingly, the fluorescence efficiency can be tailored by changing the substituent at the adjacent Cc position, which may cause either an enhancement of the emission quantum yield or a total fluorescence quenching in the case of aromatic substituents. [11][12][13][65][66][67][68][69] Anthracene is a very well-studied -conjugate system easy to functionalize and with remarkable intrinsic photophysical, photochemical and chemical properties, which make it and its derivatives ideal molecules to construct fluorophores, fluorescent probes, organic light-emitting transistors, among others. 70,71 Throughout the last years, some carboranyl-functionalized anthracene derivatives have been reported and their photoluminescence behaviour explored.…”

Carborane‐BODIPY Dyads: New Photoluminescent Materials through an Efficient Heck Coupling

“…For this purpose, we identified the two Heck coupling partners to start our investigation and optimize our target reaction with a) a properly functionalized carborane bearing a styrene moiety ( o ‐Me‐CB , o ‐Ph‐CB , m ‐Me‐Cb and m ‐Ph‐Cb ) and b) the highly fluorescent BODIPY dye 1 (Scheme ), which exhibits an absorption maximum at λ abs =502 nm. The 1,3,5,7‐tetramethyl BODIPY derivative 1 has been synthesized by an acid‐catalyzed condensation of 2,4‐dimethylpyrrole with p ‐bromobenzaldehyde, and the styrenyl‐containing carborane derivatives have been successfully synthesized by lithiation of the parent closo ‐carborane cluster followed by the addition of 4‐vinylbenzyl chloride, as described in the literature ,…”

“…Littke and Fu described in 2001 the Pd 2 (dba) 3 /Pd(P( t Bu) 3 ) 2 catalytic system in the presence of dicyclohexylmethylamine (Cy 2 NMe) as an effective tool for Heck reactions of aryl chlorides and aryl bromides, suitable for both harsh and mild conditions . The unusual effectiveness of the base, which was proven to provide a more active catalyst compared to other bases (such as Cs 2 CO 3 ), also made this versatile procedure efficient to introduce a variety of functional groups either on brominated and iodinated silicate cages (possessing similar characteristics to the carborane cluster) and on the carboranyl substrates of our interest –…”

“…As part of our studies aimed at tagging biological relevant compounds using fluorescent probes for live cell‐imaging applications, we exploited the excellent photo‐features of BODIPYs as optical probes and we recently reported the optimization of a Heck coupling‐reaction on an asymmetric aza‐BODIPY core . Likewise, styrene‐containing carborane derivatives have demonstrated to be excellent starting molecules to achieve different fluorescent materials through a Heck coupling reaction –. Therefore, we envisaged that these derivatives might represent a very suitable coupling partner for Heck reactions with halogenated BODIPY fluorophores and their aza‐analogues.…”