ABSTRACT
Deep red/near-infrared (NIR, >650â nm) emissive organic luminophores with aggregation-induced emission (AIE) behaviours have emerged as promising candidates for applications in optoelectronic devices and biological fields. However, the molecular design philosophy for AIE luminogens (AIEgens) with narrow band gaps are rarely explored. Herein, we rationally designed two red organic luminophores, FITPA and FIMPA, by considering the enlargement of transition dipole moment in the charge-transfer state and the transformation from aggregation-caused quenching (ACQ) to AIE. The transition dipole moments were effectively enhanced with a "V-shaped" molecular configuration. Meanwhile, the ACQ-to-AIE transformation from FITPA to FIMPA was induced by a methoxy-substitution strategy. The experimental and theoretical results demonstrated that the ACQ-to-AIE transformation originated from a crystallization-induced emission (CIE) effect because of additional weak interactions in the aggregate state introduced by methoxy groups. Owing to the enhanced transition dipole moment and AIE behaviour, FIMPA presented intense luminescence covering the red-to-NIR region, with a photoluminescence quantum yield (PLQY) of up to 38 % in solid state. The promising cell-imaging performance further verified the great potential of FIMPA in biological applications. These results provide a guideline for the development of red and NIR AIEgens through comprehensive consideration of both the effect of molecular structure and molecular interactions in aggregate states.
ABSTRACT
The traditional design strategies for highly bright solid-state luminescent materials rely on weakening the intermolecular π-π interactions, which may limit diversity when developing new materials. Herein, we propose a strategy of tuning the molecular packing mode by regioisomerization to regulate the solid-state fluorescence. TBP-e-TPA with a molecular rotor in the end position of a planar core adopts a long-range cofacial packing mode, which in the solid state is almost non-emissive. By shifting molecular rotors to the bay position, the resultant TBP-b-TPA possesses a discrete cross packing mode, giving a quantum yield of 15.6±0.2 %. These results demonstrate the relationship between the solid-state fluorescence efficiency and the molecule's packing mode. Thanks to the good photophysical properties, TBP-b-TPA nanoparticles were used for two-photon deep brain imaging. This molecular design philosophy provides a new way of designing highly bright solid-state fluorophores.
Subject(s)
Aniline Compounds/chemistry , Fluorescent Dyes/chemistry , Phenazines/chemistry , Thiophenes/chemistry , Aniline Compounds/radiation effects , Animals , Brain/diagnostic imaging , Fluorescent Dyes/radiation effects , HeLa Cells , Humans , Isomerism , Mice , Microscopy, Confocal , Microscopy, Fluorescence , Nanoparticles/chemistry , Nanoparticles/radiation effects , Phenazines/radiation effects , Photons , Thiophenes/radiation effectsABSTRACT
Low cost and strong fluorescence emission are two important guarantees for luminogens used as light conversion agents. By one-pot multicomponent approach and inexpensive starting materials, three dicyanopyridine (DP) derivatives named as DCP (2-amino-6-methoxy-4-phenylpyridine-3,5-dicarbonitrile), DCO (2-amino-6-methoxy-4-(4-methoxyphenyl) pyridine-3,5-dicarbonitrile) and DCC (2-amino-4-(4-cyanophenyl)-6-methoxypyridine-3,5-dicarbonitrile) were designed and synthesized. Meanwhile, the ACQ-to-AIE transformation was successfully realized by altering substituent groups rather than traditional rotor-stator theory. Based on crystal analysis and theoretical calculations, the ACQ-to-AIE transformation is attributed to the tunable stacking modes and intermolecular weak interactions. Owing to matched fluorescence emission, low lost, high yield, and AIE activity, DCC is used as light conversion agents and doped in EVA matrix. The light conversion quality confirms that DCC can not only convert ultraviolet light, but also significantly improve the transmittance of 25 %/40 % EVA, whose photosynthetic photon flux density at 400-500 nm and 600-700 nm increased to 30.67 %/30.21 % and 25.37 %/37.82 % of the blank film, respectively. After 20 h of UV irradiation (365 nm, 40 W), the fluorescence intensities of DCC films can maintain 92 % of the initial values, indicating good photostability in the doping films. This work not only provides an excellent and low-cost light conversion agent, but also has important significance for ACQ-to-AIE transformation of luminogens.