Table 1. Evolution of far-red fluorescent proteins.

/, excitation and emission maxima. E _mol, extinction coefficient. Φ_F, quantum yield. B, brightness (E _mol × Φ_F)/1000. , brightness relative to EGFP [the product of Φ_F and E _mol compared to the brightness of EGFP (53 000 M ⁻¹ cm⁻¹ × 0.60) (Patterson et al., 1997 ▶)].

FP variant	/ (nm)	E mol (M −1 cm−1)	ΦF	B		Reference
EGFP†	489/509	53000	0.60	31.8	1.00	Patterson et al. (1997 ▶)
WT progenitors
DsRed	558/583	75000	0.70	52.5	1.65	Yarbrough et al. (2001 ▶)
eqFP578	552/578	102000	0.54	55.1	1.73	Merzlyak et al. (2007 ▶)
eqFP611	559/611	78000	0.45	35.1	1.10	Wiedenmann et al. (2002 ▶)
First generation
HcRed	594/649	70000	0.05	3.5	0.11	Gurskaya et al. (2001 ▶)
mPlum	590/649	41000	0.10	4.1	0.13	Wang et al. (2004 ▶)
AQ143	595/655	90000	0.04	3.6	0.11	Shkrob et al. (2005 ▶)
Second generation
Katushka	588/635	65000	0.34	22.1	0.69	Shcherbo et al. (2007 ▶)
mKate	588/635	45000	0.33	14.9	0.49	Shcherbo et al. (2007 ▶)
RFP637	587/637	72000	0.23	16.5	0.52	Kredel et al. (2008 ▶)
RFP639	588/639	69000	0.18	12.4	0.39	Kredel et al. (2008 ▶)
Third generation
mKate2	588/633	62500	0.40	25.0	0.79	Shcherbo et al. (2009 ▶)
Neptune	600/650	72000	0.18	13.0	0.41	Lin et al. (2009 ▶)
mNeptune	600/650	67000	0.20	13.4	0.42	Lin et al. (2009 ▶)
E2-Crimson	611/646	126000	0.23	29.0	0.91	Strack et al. (2009 ▶)
TagRFP657	611/657	34000	0.10	3.4	0.11	Morozova et al. (2010 ▶)
eqFP650	592/650	65000	0.24	15.6	0.49	Shcherbo et al. (2010 ▶)
eqFP670	605/670	70000	0.06	4.2	0.13	Shcherbo et al. (2010 ▶)

^†The values for EGFP are given for comparison.