o‐Amino Analogs of Green Fluorescence Protein Chromophore: Photoisomerization, Photodimerization and Aggregation‐induced Emission

Abstract

The photochemical properties of three o-amino analogs of the green fluorescence protein chromophore O0, O1 and O8 (o-ABDIs) have been investigated and compared with those of the m- and p-amino isomers (m-ABDIs and p-ABDIs) in solutions, aggregates, and the solid state. In aprotic solvents, the fluorescence competes with the Z → E photoisomerization for all cases, and the o-ABDIs display a fluorescence quantum efficiency of 1-6%, lying between the m-ABDIs of 5-48% and the p-ABDIs of < 0.1%. The fluorescence of both the o- and m-ABDIs is nearly quenched in protic solvents, attributable to the solvent-solute hydrogen bonding (SSHB) interactions. The phenomenon of aggregation-induced emission observed for O8 in poor solvents resembles the behavior of M8 as a consequence of exclusion of the SSHB interactions and restriction of internal rotation for molecules located inside the aggregates. The occurrence of [2 + 2] photodimerization for O0 in the solid state is unique among the ABDIs, and the X-ray crystal structures of O0 and the photodimer OD reveal the head-to-tail syn-oriented stereochemistry. Analysis on the X-ray crystal structures of O0, O1, M0, M1 and P0 shows that not only the pairwise topochemical geometry but also the columnar packing mode is important in determining the photodimerization reactivity.

Aggregate Science: From Structures to Properties

“…[156,157] The green fluorescence ceases if the HBI disassembles from GFP and dissolves in buffer, indicating the AIE nature of HBI ( Figure 8A). [158][159][160] Theoretically, this effect is not limited to HBI. HBI analogs such as HBIa should also work and other proteins may be able to induce the AIE effect similarly to GFP.…”

Photo‐Responsive Fluorescent Materials with Aggregation‐Induced Emission Characteristics

“…Some studies on photodimerization based on AIEgens have been reported. [113,114] Most recently, Tang and coworkers constructed a new type of light-driven molecular crystal based on the photodimerization of 2-phenylbenzo-[b]thiophene 1,1-dioxide (P-BTO). [112] As displayed in Figure 5A, upon UV irradiation, the crystalline P-BTO undergoes photodimerization to form 2P-BTO with an unconventional conjugated structure.…”

Synthesis and Fluorescence Mechanism of the Aminoimidazolone Analogues of the Green Fluorescent Protein: Towards Advanced Dyes with Enhanced Stokes Shift, Quantum Yield and Two‐Photon Absorption

“…Some simple p ‐HOBDI analogues, such as o ‐HOBDI, [3] o ‐TsABDI, [4] p ‐TsABDI, [5] o ‐AABDI, [6] and p ‐AABDI, [7] also exhibit low QY (10 −2– 10 −4 ), and the para ‐amino analogue of p ‐HOBDI ( p ‐ABDI) is practically non‐fluorescent [8,9] . This enormous difference between the small molecule p‐ HOBDI and the GFP has incited intensive research towards the understanding of the fluorescence‐quenching mechanism in p‐HOBDI and the optimisation of the chromophore structure [2,10–14] …”

“…For instance, the change of the 4‐hydroxy group to a 4‐diethylamino group on the phenyl ring improved the QY by up to 28 times [31–33] . An even more remarkable boost in fluorescence is displayed by the amino derivatives in aprotic solvents, out of which the meta‐amino isomer was shown to have an unusually high, 0.46 QY [2,13,34] . Solvent‐ and pH‐related effects are also often enhanced by the substituents.…”