Table 2. Photophysical Properties of N-Boc-Protected Azobenzene–Alanine Analogues.

compd	X	R	trans λmax n→π* (nm)	cis λmax n→π* (nm)	n→π* separationa (nm)	trans:cis 530 nm	trans:cis 448 nm
3g	H	2,6-F2	435	427	8	34:66b	62:38b
3h	H	2,4,6-F3	439	429	10	38:62c	61:39c
3k	H	2,3,4,5,6-F5	446	428	18	43:57c	64:36c
3l	F	2,6-F2	442	426	16	36:64b	60:40b
3m	F	2,4,6-F3	436	424	12	24:76b	61:39b
3n	F	2,3,4,5,6-F5	442	429	13	35:65c	62:38c
3o	Cl	2,6-F2	428	426	2	23:77b	70:30b
3p	Cl	2,4,6-F3	425	425	0	28:72b	71:29b
3q	Cl	2,3,4,5,6-F5	448	434	15	34:66b	67:33b

^aWavelength separation was calculated using the following equation: Δ = λ_max,trans – λ_max,cis.

^bTrans/cis ratio was determined by ¹⁹F NMR.

^cTrans/cis ratio was determined by ¹H NMR. Sample was dissolved in DMSO-d₆ in an NMR tube to obtain a concentration of 15–22 mM. The photoirradiation was performed by placing the NMR tube on top of an LED light in an enclosed compartment for 30 min.