Intramolecular Charge Transfer Dynamics in Fluorescent Molecules

Intramolecular charge transfer (ICT) underpins the photophysical response of a vast array of fluorescent organic materials, governing their utility in sensing, imaging and optoelectronic devices. Upon absorption of light, electrons redistribute from an electron-donating moiety to an electron-accepting unit within the same molecule, often accompanied by significant structural reorganisation. The competition between radiative emission and non-radiative pathways is mediated by solvent polarity, molecular conformation and internal rotations, leading to phenomena such as dual fluorescence and polarity-dependent quantum yields. Ultrafast spectroscopic techniques—transient absorption, time-resolved fluorescence and ultrafast Raman—combined with quantum chemical and nonadiabatic molecular dynamics simulations have elucidated the sequence of excited-state events: initial Franck–Condon excitation, torsional relaxation towards twisted ICT (TICT) conformers, charge localisations and eventual intersystem crossing (ISC) to triplet levels or return to the ground state. These mechanistic insights enable rational design of push–pull architectures with tailored lifetimes and emission wavelengths, advancing applications from bioimaging probes to energy-harvesting systems.

Research from Nature Portfolio

Recent studies have applied time-resolved spectroscopies and quantum chemical calculations to decipher the interplay of conformational relaxation and electronic transitions in aminoanthraquinone derivatives. These investigations revealed that excitation leads to rapid twisting of the amino group, triggering an intramolecular charge transfer to a twisted internal charge-transfer (TICT) state on a picosecond timescale, followed by intersystem crossing to triplet states. The barrier along the twisted coordinate, determined by time-dependent density functional theory, governs the balance between radiative and non-radiative decay pathways, offering insights for tuning fluorescence yields in pharmaceutical chromophores.

Intramolecular Charge Transfer Dynamics in Fluorescent Molecules publication trend

The graph below shows the total number of articles in intramolecular charge transfer dynamics in fluorescent molecules across all publications each year (not limited to Nature Index journals).

Technical terms

Intramolecular Charge Transfer (ICT): Electron density redistribution between donor and acceptor units within a single molecule following photoexcitation.

Twisted Intramolecular Charge Transfer (TICT): A charge-transfer state characterised by a large torsional angle between donor and acceptor, often leading to non-radiative decay.

Intersystem Crossing (ISC): A non-radiative transition between electronic states of different spin multiplicity, commonly from singlet to triplet manifolds.

Nonadiabatic Molecular Dynamics (NAMD): A simulation approach that captures coupled electronic and nuclear motion to model excited-state relaxation pathways.

References

1. Governing the emissive properties of 4-aminobiphenyl-2-pyrimidine push–pull systems via the restricted torsion of N,N-disubstituted amino groups. Frontiers in Chemistry (2023).
2. Fluorescence Modulation by Amines: Mechanistic Insights into Twisted Intramolecular Charge Transfer (TICT) and Beyond. Chemosensors (2023).
3. Ultrafast investigation of photoinduced charge transfer in aminoanthraquinone pharmaceutical product. Scientific Reports (2017).
4. Nonadiabatic Molecular Dynamics Simulations Provide Evidence for Coexistence of Planar and Nonplanar Intramolecular Charge Transfer Structures in Fluorazene. The Journal of Physical Chemistry A (2024).