Photochemical Reactivity and CO2 Sensing Applications of Organoboron Compounds

Abstract

The works described herein are focused on the investigation of photo, thermal and CO2 responsive properties of boron-containing π-conjugated systems in order to develop an in-depth understanding of the relationship between molecular structure and photophysical properties and to further expand the application fields. Rapid progress in the field of N,C- and C,C-chelate organoboron photochromic materials over the past ten years has been focused on the impact of different π-conjugated backbones and the effects of different substituents on the chiral boron center. Despite the well-developed nature of this field, limitations still exist such as the need to have at least one bulky mesityl group present on the boron atom. To remedy this deficiency, we investigated a series of N-alkyl substituted benzylideneamines with boryl groups attached at the 2-position with the goals of simplifying the starting material structures of photoactive organoborates. Furthermore, we hoped to increase their reactivity in order to generalize their photoreactions for the preparation of a variety of B=N containing 7- and 8-membered ring systems with four different substituents on the B=N unit. Chiral N,C-chelate organoboron compounds bearing two different aryl groups (phenyl, tolyl, naphthyl) at the boron center have been found to undergo regioselectivie photoisomerization, generating various 7-membered ring systems via H-atom transfer. Furthermore, functionalized with non-bulky heterocycle substituent (thienyl) of this kind of N,C-chelate organoboron compounds enables quantitative phototransformations yielding chiral N,B,S-embedded heterocycles. The impact of intramolecular H bonding and n-π* interactions on photophysical properties of laterally appended D-π-A triarylboron compounds with biphenyl units were studied systematically. Some of these compounds have been found to display fluorescent response toward CO2. To further improve the CO2 sensing properties, three new alkylamino-appended D-π-A triarylboron have been found with the ability to capture CO2 with the formation of carbamic acid and detect CO2 with, obvious fluorescent color change, high sensitivity and good reversibility. In addition, this system is also effective as fluorescence “turn-on” temperature probes due to the dynamic B ← N bond dissociation/association.