Stereochemical modulation of emission behaviour in E/Z isomers of diphenyldipyrroethene from aggregation induced emission to crystallization induced emission

Abstract

Herein, we report the synthesis, separation and characterisation of the E- and Z-isomers of dipyrrolyldiphenylethene to study their emission behaviour in the aggregation state and solid state. The E-isomer showed pronounced aggregation induced emission (AIE) whereas the Z-isomer showed crystallization induced emission (CIE). The present study explains that the emission behaviour (AIE/CIE) is dependent on the inter/intra molecular interactions between the molecules. The study also confirms that restriction of intramolecular rotation (RIR) is the main cause of AIE/CIE in olefinic luminogens Tetraphenylethylene (TPE) type systems rather than E/Z isomerisation.

Structure‐Dependent cis/trans Isomerization of Tetraphenylethene Derivatives: Consequences for Aggregation‐Induced Emission

“…[2] Carbon-carbon double bonds are also built-in elements of fluorescent dyes whose cis and trans isomers display different optical properties. [8] Thef ew separated isomers display different mechanochromic properties, [8a] and the corresponding probes show distinct biological responses to target enzymes. [4] These unique AIE properties are the opposite to the aggregation-caused quenching (ACQ) observed for conventional fluorophores.…”

“…[5] AIEgens thus provide an ovel and complementary approach for the design of new-generation fluorescent probes. [8] This approach is tedious and only applicable to those isomers that can easily grow into single crystals.O wing to these difficulties,m ixtures of the cis and trans isomers were reported and used in most studies, [11] which has compromising effects on the functions and properties of these molecules in various applications.W ith these considerations in mind, we herein designed and synthesized various analogues of atetraphenylethenethiophene derivative (TPETH), namely TPETH-OH, TPETH-MAL, and TPETH-cRGD (Scheme 1). Thus far, multiple functional groups have been attached to the phenyl rings of TPE to fine-tune its optical properties for sensing,i maging,a nd therapeutic applications.…”

“…[6] TPE, as an iconic AIEgen, has attracted tremendous research interest. [8] Thef ew separated isomers display different mechanochromic properties, [8a] and the corresponding probes show distinct biological responses to target enzymes. [7] Previous studies have shown that the majority of the TPE derivatives do not undergo photoinduced cis/trans isomerization under the conditions normally applied for photoluminescence spectroscopy.…”

“…[8] Thef ew separated isomers display different mechanochromic properties, [8a] and the corresponding probes show distinct biological responses to target enzymes. [8] This approach is tedious and only applicable to those isomers that can easily grow into single crystals.O wing to these difficulties,m ixtures of the cis and trans isomers were reported and used in most studies, [11] which has compromising effects on the functions and properties of these molecules in various applications.W ith these considerations in mind, we herein designed and synthesized various analogues of atetraphenylethenethiophene derivative (TPETH), namely TPETH-OH, TPETH-MAL, and TPETH-cRGD (Scheme 1). For example,p alladium-catalyzed coupling reactions can be employed to directly synthesize pure isomers, [10] but generally mainly the cis product is formed while the isomeric purity of the obtained product is not very high.…”

“…For example,p alladium-catalyzed coupling reactions can be employed to directly synthesize pure isomers, [10] but generally mainly the cis product is formed while the isomeric purity of the obtained product is not very high. [8] This approach is tedious and only applicable to those isomers that can easily grow into single crystals.O wing to these difficulties,m ixtures of the cis and trans isomers were reported and used in most studies, [11] which has compromising effects on the functions and properties of these molecules in various applications.W ith these considerations in mind, we herein designed and synthesized various analogues of atetraphenylethenethiophene derivative (TPETH), namely TPETH-OH, TPETH-MAL, and TPETH-cRGD (Scheme 1). [8a] After successful separation, confirmation of the cis/trans geometry is another challenging task.…”