Cyan Emissive Polyethyleneimine: Exploration of Fluorescence Mechanism for Real Applications

ABSTRACT A robust method is reported here for synthesizing a non‐conjugated non‐aromatic fluorescent polymer (NNFP) using branched polyethyleneimine (PEI) and citric acid (CA) as precursors through an amide condensation reaction in the aqueous medium. The as‐prepared NNFP is well‐dispersed in water, which shows aggregation‐induced emission (AIE) and excitation‐independent bright cyan fluorescence having a high quantum yield (QY) (30.83%). The designed product exhibits excellent solid‐state fluorescence suitable for developing optical devices. The emission can be attributed to the compact structure of NNFP, which promotes the fluorescence resonance energy transfer (FRET) (hydroxyl donor; CONH acceptor; donor‐acceptor distance: 1.2 nm). The intensity ratio ( I 360 : I 252 ) in the excitation spectrum measures the number average ratio of OH and CONH groups of the NNFP. The designed NNFP has a large stoke shift (446 − 245 = 201 nm), indicating its higher anti‐interference ability in practical applications compared to the general fluorescent materials. The geometry optimization and FMO analysis help to understand the optical properties of the modified polymer. The NNFP can be used as an excellent fluorescent probe to detect Fe 3+ and F − in aqueous solutions. An attempt has been made to develop an excellent fluoro‐ink for security purposes (i.e., a secret message delivery).