Peddaboodi Gopikrishna

Functional 1,8-Naphthalimide AIE/AIEEgens: Recent Advances and Prospects

This comprehensive review surveys the up-to-date development of aggregation-induced emission/aggregation-induced emission enhancement (AIE/AIEE) active naphthalimide (NI)-based smart materials with potential for wide and real-world applications and that serves as a highly versatile building block with tunable absorption and emission in the complete visible region. The review article commences with a precise description of the importance of NI moiety and its several restricted area of applications owing to its aggregation caused quenching (ACQ) properties, followed by the discovery and importance of AIE/AIEE-active NIs. The introduction section tracked an overview of the state of the art in NI luminogens in multiple applications. It also includes a few mechanistic studies on the structure-property correlation of NIs and provides more insights into the condensed-state photophysical properties of small aggregation-prone systems. The review aims to ultimately accomplish current and forthcoming views comprising the use of the NIs for the detection of biologically active molecules, such as amino acids and proteins, recognition of toxic analytes, fabrication of light emitting diodes, and their potential in therapeutics and diagnostics.

Bridge-driven aggregation control in dibenzofulvene–naphthalimide based donor–bridge–acceptor systems: enabling fluorescence enhancement, blue to red emission and solvatochromism

Four novel 1,8-naphthalimide (NC) and mono-substituted dibenzofulvene (DBF) based structures have been designed and successfully synthesized. Two luminogens were substituted by a thiophene bridge (DT1NC and DT2NC), while the other two luminogens were substituted by a phenyl bridge (DP1NC and DP2NC) between the NC and DBF units. This minor structural modification crafts striking changes in the photophysical behavior. DT1NC and DT2NC displayed aggregation induced emission enhancement (AIEE) behavior. They also showed orange and red emission (575 nm and 602 nm), respectively, with large bathochromic shifts (35 nm and 112 nm) and high quantum yields (84.10% and 65.65%) in the aggregated state because of ladder type J-aggregation. DP1NC exhibited weak AIEE behavior in the blue region, while DP2NC showed an AIE inactive nature because of the strong C–H⋯π intermolecular interactions. All the luminogens showed positive solvatochromism caused by intramolecular charge transfer (ICT). The DT2NC and DP2NC luminogens were substituted with two bromine atoms at the 2,7 positions of the DBF moiety, but unexpectedly only DT2NC showed a strong heavy atom effect. Theoretical and experimental HOMO and LUMO energy levels were estimated by density functional theory and cyclic voltammetry, respectively. All luminogens displayed excellent thermal stabilities and good morphological behavior.

Highly efficient and facile alkylation of 4H-cyclopenta-[2,1-b:3,4-b′]dithiophene in water

A new and highly convenient method to perform alkylation of 4H-cyclopenta-[2,1-b:3,4-b′]dithiophene (CPDT) in aqueous conditions is reported. This method was also extended to successfully perform alkylation of 2,6-dibromo-4H-cyclopenta-[2,1-b:3,4-b′]dithiophene for the first time. This facile method has several advantages such as the exclusive use of water instead of high boiling toxic solvents, simple separation of the defect free dialkylated CPDT product and the use of mild reaction conditions. Despite using mild reagents and reaction conditions, to our delight, very high yields of up to 98% pure dialkylated CPDT products are obtained much more readily by this method in less time than literature procedures. The isolated products were identified by HRMS and solution NMR measurements to be solely the desired dialkylated product with the alkyl halides used here.

Receptor-Free Detection of Picric Acid: A New Structural Approach for Designing Aggregation-Induced Emission Probes

A pristine aggregation-induced enhanced emission (AIEE) active monomer 2,5-bis(( E)-4-bromostyryl)-3,4-diphenylthiophene (TPBZ) and its copolymer (PFTPBZ) with 9,9-dioctylfluorene-2,7-diboronic acid bis(1,3-propandiol) ester have been synthesized via Suzuki coupling polymerization. PFTPBZ that is devoid of any receptor showed AIEE property and demonstrated excellent and selective fluorometric recognition of 2,4,6-trinitrotoluene (TNT) in aggregated state (aqueous medium) and picric acid (PA) in aggregated state and solution state (organic solvent) as well as in vapor phase via PFTPBZ dip-coated Whatman filter paper on a solid-phase platform in 1.86 ng level (naked eye). Limit of detection (LOD) for TNT in 95% water fraction ( fw) was 53.74 × 10-6 M, and at 40% fw, it was 14.26 × 10-7 M. PA detection in tetrahydrofuran solution was possible with a LOD of 28.16 × 10-7 M, 95% fw with LOD of 10.47 × 10-6 M, and in 40% fw with LOD of 47.39 × 10-8 M. As a unique example of structural design, the probe PFTPBZ surprisingly possesses no receptor, yet remarkably high selectivity was achieved via Förster resonance energy transfer (FRET) and photoinduced electron transfer from the copolymer PFTPBZ to PA and TNT. Detection of PA in the presence of various metal analytes and inorganic acids in real water samples (lakes, rivers, and sea water) was also demonstrated using this concept of receptor-free conjugated polymer probe.