Visible‐Light Mesoinoic Oxidopyrylium Ylide Photoswitches for Multicolor Photochromism and Dual‐λ Synergistic Photoclick Reactions with Dibenzo[ <i>b</i> , <i>f</i> ][1,4,5]Thiadiazepine‐Dioxide

ABSTRACT State‐of‐the‐art photoclick chemistry leverages photoswitches as dipole/dipolarophile sources for dynamic reactant recovery and spatiotemporal precision in complex environments. Despite rareness, dual‐wavelength (λ) synergy via two orthogonal photoswitch precursors promises dual‐λ accelerated reaction rates and higher‐dimensional control. Here, we introduce thiophene‐fused 2,3‐diaryl indenone epoxides (DIOs) that undergo P‐type photoswitching to mesoionic oxidopyrylium ylides (PYs as bistable photochromic dipole) controlled by visible light. These DIOs derivatives exhibit multicolor photochromism in polymer matrices under sequential irradiation, functioning as dynamic photochromic materials. By coupling the DIO⇌PY P‐type photoswitch with a unique T‐type photoswitch (thermally reversible), dibenzothiadiazepine‐dioxide (DBTDD) as a ring‐strain loadable dipolarophile, we develop a robust [5+2] photoclick reaction. Synergistic dual‐λ stimulation (405 + 445 nm) achieves a remarkable 27‐fold rate acceleration (up to 1.6 × 10 5 M −1 s − 1 ) and dual‐λ orthogonal photo‐control for protein labeling, outperforming the benchmarks, e.g., bicyclo[6.1.0]non‐4‐yn‐9‐ylmethanol (BCN‐OH) and dibenzothiadiazepine (DBTD). The P‐type photoisomerization mechanism of the DIO⇌PY system is clarified for the first time via theoretical calculations together with experimental validation, revealing competitive singlet/triplet diradical pathways during photo‐ring‐opening/closure cycles. Transition‐state analyses rationalize the superiority of DBTDD over DBTD in the [5+2] cycloaddition, offering mechanistic insights and principles for advancing the dual‐λ photoclick platform.