Twisted intramolecular charge transfer (TICT) and twists beyond TICT: from mechanisms to rational designs of bright and sensitive fluorophores

Abstract

The twisted intramolecular charge transfer (TICT) mechanism and twists beyond TICT have guided the creation of numerous bright and sensitive fluorophores. We reviewed the structure–property relationships of these dyes with representative examples.

Highly Efficient TADF‐Type Organic Afterglow of Long Emission Wavelengths

“…UV‐Vis studies of Me 2 TPABF 2 dilute solutions in n ‐hexane, ethyl acetate and acetone have also been performed, all of which show typical ICT absorption behaviors (Figure 1e). [ 52 ] Upon excitation at 420 nm, Me 2 TPABF 2 molecules display emission bands at 523 nm ( Φ = 50.3%, τ = 5.37 ns) in n ‐hexane, at 540 nm ( Φ = 1.3%, τ = 3.06 ns) in ethyl acetate, and at 583 nm in acetone ( Φ = 0.1%, τ = 1.09 ns) (Figure 1f). Me 2 TPABF 2 powders exhibit bright yellow emission under 365 nm UV excitation source (λ em = 583 nm, Φ = 42.3%, τ 1 = 2.27 ns (50.5%), τ 2 = 4.03 ns (49.5%)), whereas no room‐temperature afterglow has been observed upon ceasing the excitation source (Figures S5 and S6, Supporting Information).…”

“…Actually, according to the studies by Adachi's group and our group, a high T 1 level of organic matrices is very important for the fabrication of high-performance afterglow materials since it can avoid afterglow quenching caused by triplet-to-triplet energy transfer from luminescent dopants to organic matrices. [50][51][52]72] The present two-component system, because of its flexibility in component selection, has the advantage to allow systematic variation of the chemical structures of organic matrices to reveal the underlying photophysics and the role of the organic matrices. BP derivatives, such as MeBP and MeOBP (Figure 2a), have been used as organic matrices for the fabrication of afterglow materials (Text S3, Supporting Information).…”

A General Method to Develop Highly Environmentally Sensitive Fluorescent Probes and AIEgens

“…[ 30 , 31 ] Encouraged by its outstanding environmental sensitivities, i.e., TICT‐induced quenching in polar solvents, we predicted that MP‐NAP could also show outstanding AIE behaviors as molecular aggregation could effectively reduce local polarities and hinder TICT rotations. [ 9 , 21 ] Moreover, the steric hindrance (with a pretwisted molecular structure) may also help to minimize intermolecular π ‐ π interactions for avoiding aggregation‐caused quenching (ACQ), thus endowing MP‐NAP with bright emissions in molecular aggregates and the solid state.…”

“…[ 1 , 2 ] Fluorescent output (i.e., intensities, wavelengths, or lifetime) of these probes experience substantial changes in response to analytes or environmental changes, thus allowing both qualitative and quantitative detections. [ 3 , 4 ] To this end, the twisted intramolecular charge transfer (TICT) [ 5 , 6 , 7 , 8 , 9 ] mechanism has been extensively utilized in developing numerous fluorescent probes, [ 9 ] such as viscosity sensors, [ 10 , 11 ] polarity probes, [ 12 ] temperature sensors, [ 13 ] and chemical probes. [ 14 ] Yet, owing to their weak TICT tendencies, the environmental sensitivities of many biocompatible main‐stream fluorophores (such as coumarin and rhodamine derivatives) remain suboptimal.…”

NIR-II Aggregation-Induced Emission Luminogens for Tumor Phototheranostics

“…Using reverse thinking of the AIE process, researchers devised numerous strategies to maximize molecular motion in the aggregated state of AIEgens to exhibit superior heat transitions without compromising FLI [ 37 ]. In addition, it was found that twisted intramolecular charge transfer (TICT) states in AIEgens typically abate the fluorescence signals but enhance their photothermal capability, which quickly sparked strong interest among researchers [ 38 , 39 , 40 ].…”