Abstract:The Hula-Twist (HT)
photoreaction represents a fundamental
photochemical
pathway for bond isomerizations and is defined by the coupled motion
of a double bond and an adjacent single bond. This photoreaction has
been suggested as the defining motion for a plethora of light-responsive
chromophores such as retinal within opsins, coumaric acid within photoactive
yellow protein, or vitamin D precursors, and stilbenes in solution.
However, due to the fleeting character of HT photoproducts a direct
experimental obser… Show more
The pursuit of sensitive fluorescent chromophores with integrated aggregation‐induced emission (AIE) and twisted intramolecular charge transfer (TICT) properties are attractive due to the tunable emission properties and increased intensity. However, this type of chromophore has yet to be exemplified mechanistically. In this study, a strategy is presented for manipulating the formation of TICT and the AIE effect through molecular engineering. The feasibility of TICT properties is validated by theoretical calculations and ultrafast spectroscopies. By precisely adjusting the hydrophobicity of the donor group, the fluorescence is significantly enhanced through the addition of poor solvent. These findings not only provide mechanistic elucidation for chromophores exhibiting integrated TICT and AIE properties in various environmental conditions but also underscore the critical factors for the systematic design of chromophores with high tunability and strong emissions.
The pursuit of sensitive fluorescent chromophores with integrated aggregation‐induced emission (AIE) and twisted intramolecular charge transfer (TICT) properties are attractive due to the tunable emission properties and increased intensity. However, this type of chromophore has yet to be exemplified mechanistically. In this study, a strategy is presented for manipulating the formation of TICT and the AIE effect through molecular engineering. The feasibility of TICT properties is validated by theoretical calculations and ultrafast spectroscopies. By precisely adjusting the hydrophobicity of the donor group, the fluorescence is significantly enhanced through the addition of poor solvent. These findings not only provide mechanistic elucidation for chromophores exhibiting integrated TICT and AIE properties in various environmental conditions but also underscore the critical factors for the systematic design of chromophores with high tunability and strong emissions.
In this study, a well-defined organic capsule assembled from two octa acid (OA) molecules acting as host and select arylazoisoxazoles (AAIO) acting as guests were employed to demonstrate that confined molecules have restricted freedom that translates into reaction selectivity in both ground and excited states. The behavior of these AAIO guests in confined capsules was found to be different from that found in both crystals, where there is very little freedom, and in isotropic solvents, where there is complete freedom. Through one-dimensional (1D) and two-dimensional (2D) 1 H NMR spectroscopic experiments, we have established a relationship between structure, dynamics and reactivity of molecules confined in an OA capsule. Introduction of CF 3 and CH 3 substitution at the 4-position of the aryl group of AAIO reveals that in addition to space confinement, weak interactions between the guest and the OA capsule control the dynamics and reactivity of guest molecules. 1 H NMR studies revealed that there is a temperature-dependence to guest molecules tumbling (180°rotation along the capsular short axis) within an OA capsule. While 1 H NMR points to the occurrence of tumbling motion, MD simulations and simulation of the temperature-dependent NMR signals provide an insight into the mechanism of tumbling within OA capsules. Thermal and photochemical isomerization of AAIO were found to occur within an OA capsule just as in organic solvents. The observed selectivity noted during thermal and photo induced isomerization of OA encapsulated AAIOs can be qualitatively understood in terms of the well-known concepts due to Bell−Evans− Polanyi (BEP principle), Hammond and Zimmerman.
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