3′-OH unblocked, fast photocleavable terminating nucleotides and methods for nucleic acid sequencing

1. A system comprising:

a flowcell comprising a plurality of beads, wherein:

each bead attached to a DNA or RNA molecule, wherein a compound according to any one of formulas I-VII has been incorporated into the DNA or RNA molecule using a polymerase, wherein formulas I-VII are defined as follows:

wherein:

R 1 is triphosphate or α-thiotriphosphate;

R 2 is hydrogen or hydroxy;

R 3 is alkyl (C≦8) or substituted alkyl (C≦8) ;

R 4 is

 hydrogen, hydroxy, halo, amino, nitro, cyano, azido or mercapto;

 alkyl (C≦6) , acyl (C≦6) , alkoxy (C≦6) , acyloxy (C≦6) , alkylamino (C≦6) , dialkylamino (C≦6) , amido (C≦6) , or a substituted version of any of these groups;

R 5 is a -linker-reporter, wherein the reporter is based on a dye;

R 6 is:

 hydrogen, hydroxy, halo, amino, nitro, cyano, azido or mercapto;

 alkyl (C≦6) , alkenyl (C≦6) , alkynyl (C≦6) , aryl (C≦6) , aralkyl (C≦8) , heteroaryl (C≦6) , acyl (C≦6) , alkoxy (C≦6) , acyloxy (C≦6) , alkylamino (C≦6) , dialkylamino (C≦6) , amido (C≦6) , or a substituted version of any of these groups;

or a salt, tautomer, or optical isomer thereof; and

the flowcell is at least partially transparent to visible and UV light;

an imaging device configured to capture images of the flowcell;

a filter wheel comprising at least four spectral filters, wherein the filter wheel is configured to cycle between each filter;

a lamp configured to create a light path from the flowcell through a filter in the filter wheel to the imaging device; and

an ultraviolet light source configured to provide ultraviolet light to the DNA molecules on the flowcell.

2. The system of claim 1 , wherein the flowcell is a microfluidic flowcell.

3. The system of claim 1 , further comprising an objective lens between the filter wheel and the flowcell.

4. The system of claim 1 , further comprising a mirror configured to direct the light path to the imaging device.

5. The system of claim 1 , wherein the compound is further defined as a compound of formula (I).

6. The system of claim 1 , wherein the compound is further defined as a compound of formula (II).

7. The system of claim 1 , wherein the compound is further defined as a compound of formula (III).

8. The system of claim 1 , wherein the compound is further defined as a compound of formula (IV).

9. The system of claim 1 , wherein the compound is further defined as a compound of formula (V).

10. The system of claim 1 , wherein the compound is further defined as a compound of formula (VI).

11. The system of claim 1 , wherein the compound is further defined as a compound of formula (VII).

12. The system of claim 1 , wherein R 1 is a triphosphate.

13. The system of claim 1 , wherein R 1 is an α-thiotriphosphate.

14. The system of claim 1 , wherein R 3 is alkyl (C≦8) .

15. The system of claim 14 , wherein R 3 is alkyl (C3-4) .

16. The system of claim 15 , wherein R 3 is tert-butyl.

17. The system of claim 1 , wherein R 4 is hydrogen.

18. The system of claim 1 , wherein the linker of the -linker-reporter is:

wherein

X is

—O—, —S—, or —NH—; or

alkanediyl (C≦12) , alkenediyl (C≦12) , alkynediyl (C≦12) , arenediyl (C≦12) , heteroarenediyl (C≦12) , or a substituted version of any of these groups; and

n is an integer from 0-6.

19. The system of claim 18 , wherein X is —C≡C—.

20. The system of claim 18 , wherein n is zero.

21. The system of claim 1 , wherein the dye is a zanthene, fluorescein, rhodamine, BODIPY, cyanine, coumarin, pyrene, phthalocyanine, phycobiliprotein, or a squaraine dye.

22. The system of claim 1 , wherein the reporter is:

23. The system of claim 1 , wherein R 6 is hydrogen.

24. The system of claim 1 , wherein the starred carbon atom is in the S configuration.