Table 1.

Photophysical properties of Fl-DIBO 1 as well as cycloadducts 5–7, 10b–d, and 11a–b in MeOH at 298K.

Compound	λabs [nm]	εabs [M−1.cm−1]a	λem [nm]	ΦFb	c	EF d
Fl-DIBO 1e	420	150	574	0.002	0.3	1
5 e	364	4,600	489	0.12	550	1,800
6	345	1,330	-	<0.001	1	3
7	363	19,250	514	0.016	300	1,000
10b	350	1,300	n.d.	0.001	1	3
10c	361	3,000	n.d.	0.002	6	20
10d	370	2,100	n.d.	0.002	4	13
11a	360	13,400	463	0.30	4000	13,000
11b	370	10,600	469	0.32	3400	11,000

^aDetermined at 370 nm.

^bFluorescence quantum yield, quinine sulfate in 1.0 N H₂SO₄ as standard.

^cProduct of the extinction coefficient (at 370 nm) and the fluorescence quantum yield (ε_absΦ_F).

^dEnhancement factor of the fluorophore brightness relative to Fl-DIBO 1.

^eData from reference^[22].