abstract |
Compounds having the formula (I) are provided: Embedded image Wherein one of R 1 and R 2 is a group of formula (a), wherein R 4 is selected from H and hydrocarbyl, R 5 is a hydrocarbyl group, and L is optional Or R 1 and R 2 together form a ring substituted with a group (formula (a)), wherein R 3 is H or a substituent; Wherein X is selected from S, O, NR 6 and C (R 7 ) (R 8 ), wherein R 6 is selected from H and a hydrocarbyl group, wherein R 7 and R 8 Each is independently selected from H and hydrocarbyl groups. |