We claim:

1. A compound of formula I :

Formula I

wherein, independently for each occurrence,

R is C^a and R' is C^b in a ring system selected from the group consisting of:

R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, and R¹¹ are selected from the group consisting of H, OH, halide, alkyl, alkoxy, aryl, heteroaryl, alkenyl, alkynyl, CN, acyl, and aryloxy;

at least one of R¹⁰ and R¹¹ is H; and

X is selected from the group consisting of S, Se, O, and NR¹²; and

R¹² is selected from the group consisting of H and alkyl.

2. The compound of claim 1, wherein X is S.

3. The compound of claim 1 , wherein R and R' are represented by

(A)

The compound of claim 1, wherein R and R' are represented by

5. The compound of claim 1, wherein τ

R-> 4⁴, τ

R-> 6, τ R-> 7', R⁸, R >9^y, „ R1¹0^U, and R , 1¹1¹ are H 6. The compound of claim 1, wherein X is S; and R and R' are represented by

1. The compound of claim 1 , wherein X is S; and R and R' are represented by

8. The compound of claim 2, wherein R and R' are represented by

and R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, and R⁹ are H.

9. The compound of claim 2, wherein R and R' are represented by

and R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, and R⁹ are H.

10. A compound of formula II :

Formula I I

wherein R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹, R¹², R¹³, R¹⁴, R¹⁵, and R¹⁶ are independently selected from the group consisting of H, OH, halide, alkyl, alkoxy, aryl, heteroaryl, alkenyl, alkynyl, CN, acyl, aralkyl, and aryloxy.

11. The compound of claim 10, wherein R ι l¹, r R>2, _n R6 R7', _n RS⁸ H

, _n , _n R9^y, „ R1¹0^U, r R> ¹¹, r R> 1¹2 R¹³, R¹⁴, R¹⁵, and R¹⁶ are H.

12. A compound of formula III :

wherein R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹, R¹², R¹³, R¹⁴, R¹⁵, and R¹⁶ are independently selected from the group consisting of H, OH, halide, alkyl, alkoxy, aryl, heteroaryl, alkenyl, alkynyl, CN, acyl, aralkyl, and aryloxy.

13. The compound of claim 12, wherein R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹, R¹²,

R , 1¹3^J, R 14 R¹⁵, and R¹⁶ are H.

14. A compound of formula IV :

Formula IV

15. A compound of formula V :

16. A semiconductor comprising a compound of any one of claims 1-15.

17. A field effect transistor comprising a semiconductor of claim 16.

18. A radio frequency identification device comprising a semiconductor of claim 16.

19. A photovoltaic device comprising a semiconductor of claim 16.