The Dual‐State Luminescent Mechanism of 2,3,4,5‐Tetraphenyl‐1H‐pyrrole

Abstract

2,3,4,5-Tetraphenyl-1H-pyrrole (TePP) was synthesized by a simple one-step reaction. The compound showed a balanced emission in both the solution and solid state with the absolute quantum yield of Φ =65.6 % and Φ =74.3 %, respectively. Temperature and viscosity variation measurements demonstrated that the phenyl group at the 1-position (N-position) of the pyrrole core can act as a rotor in pyrrole-based molecules, which can consume the excited energy and reduce the molecular emission in solution. TePP without the phenyl group at the 1-position can effectively enhance the emission in solution. Single-crystal analysis showed that the phenyl groups at the 2,5-positions of pyrrole extend the molecular conjugation and lock the conformation. The phenyl groups at the 3,4-positions with a twisted conformation prevent their molecules from close packing and are helpful for aggregated emission. A delicate balance between the twisting conformation and rigid conjugation takes advantage of both ACQ and AIE luminogens. The strategy can tune the AIE, ACQ, or solution and solid dual-state emission properties of pyrrole-based molecules by simply altering the position of phenyl groups, which provides a great opportunity to explore the luminescent mechanism in greater detail and to facilitate practical applications.

A Facilely Synthesized Dual‐State Emission Platform for Picric Acid Detection and Latent Fingerprint Visualization

“…To overcome this issue, in 2001, Ta ng and co-workersp roposed an ew concept of "aggregation-induced emission" (AIE), [26] in which AIE luminogens (AIEgens) usually exhibit no or poorly emissivec haracteristics in dilute solution, but emit intensely in the aggregated state. [27][28][29][30][31] By using these highly emissive AIEgens, dual-state emission can be easily achieved and they have potential real-world applications, [32][33][34] such as in PA detection and LFP visualization. Recently,f lexible alkyl chains were introduced into conventionalf luorescent molecules to prevent close packing of their core structures as well as strong p-p intermolecular stacking interactions, [35][36][37] thereby openingr adiative channels to afford highlye missive features in aggregates.T herefore, based on these considera-tions, to achieve ah ighly efficient dual-state emission platform for PA detection and LFP visualization,i nt his work, flexible alkyl chains were facilelya ttached to the commercial organic dye 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA)t o afford the tetraalkyl 3,4,9,10-perylenetetracarboxylate target compounds PTCA-C4, PTCA-C6, and PTCA-C12 (fort he structures, see Figure 1).…”

A novel strategy for realizing dual state fluorescence and low-temperature phosphorescence

“…Our previous results demonstrated that the phenyl group at the 1-position of the pyrrole ring acts as a rotor, consumes the excited state energy and lowers the emission in solution. 27 Therefore, the increase in the rotational barrier at the 1-position will effectively restrict the intramolecular motion allowing the materials to have bright fluorescence in solution (Scheme 1). This strategy can change the TPP-based molecules with both AIE and ACQ properties to molecules with DSE properties by simply extending the conjugation length at the 1-position of the pyrrole molecule.…”

“…Recently, our group developed a series of polyarylpyrroles such as triphenylpyrrole isomers (TPP-1,2,4, TPP-1,2,5 and TPP-1,3,4), tetraphenylpyrrole (TePP) and pentaphenylpyrrol (PPP) (Scheme 1). [25][26][27] Their AIE and ACQ as well as DSE properties were determined by the position of the corresponding phenyl substitution. 27 A phenyl group attached to the 1-position of the pyrrole ring can act as a rotor that consumes the energy of the excited state.…”

“…[25][26][27] Their AIE and ACQ as well as DSE properties were determined by the position of the corresponding phenyl substitution. 27 A phenyl group attached to the 1-position of the pyrrole ring can act as a rotor that consumes the energy of the excited state. Thus, removing a phenyl group attached to the N atom would effectively enhance the molecular emission in solution allowing TePP to have DSE properties.…”

“…Thus, removing a phenyl group attached to the N atom would effectively enhance the molecular emission in solution allowing TePP to have DSE properties. 27 On the other hand, as the volume of the group at the 1-position increases, the corresponding rotational barriers also increase, which will effectively restrict the intramolecular motion, allowing materials to have bright fluorescence in solution. Based on this strategy, we designed and synthesized nine compounds demonstrating 33-55% absolute quantum yields in both solution and solid states.…”