Representative types of boron-based molecular systems that respond to external stimuli such as temperature, pressure, light, or chemicals (oxygen, acid, base etc.) are described in this review article. The boron molecules are classified according to their operating mechanisms, with emphasis on systems, which are based on switchable boron-donor bonds and switchable excited states.

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Asymmetric N,C-chelate organoboron compounds bearing two different aryl groups at the boron center undergo photoisomerization reactions that involve exclusively the less bulky aryl group, generating various strongly colored "dark isomers". These species thermally isomerize to 4bH-azaborepin molecules by direct hydrogen atom transfer from a borirane cycle to the pyridyl moiety and ring expansion. Mechanistic insight into these highly regioselective transformations was obtained from kinetic data and through computational studies.

An aldehyde functionalized amino-borane has been found to respond to multiple external stimuli such as temperature, pressure and solvents, producing distinct patterns and colours.

New BN-heterocyclic compounds have been found to undergo double arene photoelimination, forming rare yellow fluorescent BN-pyrenes that contain two BN units. Most significant is the discovery that the double arene elimination can also be driven by excitons generated electrically within electroluminescent (EL) devices, enabling the in situ solid-state conversion of BN-heterocycles to BN-pyrenes and the use of BN-pyrenes as emitters for EL devices. The in situ exciton-driven elimination (EDE) phenomenon has also been observed for other BN-heterocycles.

Spiro-BODIPYs with a diaryl chelate unit have been found to form J-aggregates in methanol-water solvent mixture and brightly emissive in the solid state. The diaryl chelate unit has a significant impact on J-aggregates and fluorescence of BODIPYs. Crystal structural analysis reveals that the spiro-structures facilitate J-stacking in the solid state.

B(npy)Ar 2 (npy = 2-(naphthalen-1-yl)pyridine) compounds bearing various nonbulky aryl groups undergo ac lean and sequential two-step photoisomerization in which two aryl substituents on boron migrate to acarbon atom of the naphthyl moiety.T he second isomerization step is the first example of areversible photoisoermization between aborepin and ab orirane.B oth steric and electronic factors have been found to have ag reat impact on this photoreactivity.F urthermore,t he borirane isomer reacts with oxygen, forming ar are oxaborepin dimer.

Boranes with the general formula of HBR2 have been found to undergo a facile 1,1-hydroboration reaction with pyrido[1,2-a]isoindole (A), resulting in insertion of a BR2 unit into a CN bond and the formation of a variety of BN heterocycles. Investigation on the thermal reactivity of the BN heterocycles revealed that these molecules have two distinct and competitive thermal elimination pathways: HBR2 elimination (or retro-hydroboration) versus RH elimination, depending on the R group on the B atom and the chelate backbone. Mechanistic aspects of these highly unusual reactions have been established from both experimental and computational evidence. Adduct formation between HBR2 and A was found to be the key intermediate in 1,1-hydroboration of A.