Removal of dyes using polymers of intrinsic microporosity (PIMs): a recent approach.

Removal of dyes from various industrial effluents is a great challenge, and cost-effective methods and materials with high dye removal efficacy are in high demand. Adsorption, nanofiltration and photocatalytic degradation are three major techniques that have been investigated for dye removal. PIMs are promising materials for use in these three methods based on their attributes, such as microporosity, solution processibility, high chemical stability and tunability through facile synthesis and easy postmodification.

Helicity as a steric force: stabilization and helicity-dependent reversion of colored o-quinonoid intermediates of helical chromenes.

Photolysis of regioisomeric helical chromenes 1 and 2 leads to colored reactive intermediates. While the latter generally decay quite rapidly, they are found to be longer lived in 1 and highly persistent in 2. The remarkable stability of the otherwise fleeting transient in 2 allowed isolation and structural characterization by X-ray crystallography.

Through-space control of the persistence of photogenerated o-quinonoid intermediates in naphthalenes containing cofacially oriented chromenes and arenes.

Remarkable modulation of the persistence of the photogenerated colored o-quinonoid intermediates via a through-space interaction has been demonstrated in chromenes 1-4 based on 1,8-diarylnaphthalenes. Polar/π interaction is shown to stabilize the closed form of 4 to such an extent that photoinduced coloration is virtually invisible, while the same stabilization in the opened form of 2 permits ready coloration with a long-lived o-quinonoid intermediate.

Influence of (2,3,4,5,6-pentamethyl/phenyl)phenyl scaffold: stereoelectronic control of the persistence of o-quinonoid reactive intermediates of photochromic chromenes.

Regioisomeric photochromic chromenes 1Ch-6Ch substituted with the (2,3,4,5,6-pentamethyl/phenyl)phenyl scaffold were designed to delve into stereoelectronic effects on the spectrokinetic properties of photogenerated o-quinonoid reactive intermediates. While the latter derived from 1Ch, 2Ch, 4Ch, and 5Ch were found to exhibit notable persistence, those from 3Ch and 6Ch were found to revert rapidly at room temperature to preclude visible coloration. The intermediates of 1Ch and 2Ch were found to be marginally more stable than those of 4Ch and 5Ch, respectively, attesting to the possibility of toroidal conjugation via C(ipso)-π orbitals in the former.