Table 1.

Experimental (solvent: ACN) and theoretical (TDDFT) characteristics of 1, 2 and 3.

Entry	Compound (% endo/exo-enol)	Experimentala		Calculated (TDDFT)b						Transition (% endo/exo-enol)c	Assignment
		${\mathit{\lambda }}_{\mathit{max}}^{\mathit{exp}}$	εexp	Endo-enol			Exo-enol
				${\mathit{\lambda }}_{\mathit{max}}^{\mathit{calc}}$	f	εcalc	${\mathit{\lambda }}_{\mathit{max}}^{\mathit{calc}}$	f	εcalc
1	1 (91/9)	224	10300	224	0.17	11300	225	0.04	2600	H→L+1 (82/96)	π→ π∗
2		312	12900	298	0.31	20800	292	0.26	17900	H→L (98/96)	n→ π∗
3	2 (100/0)	212	28500	202	0.21	14100	–	–	–	H-1→L+1 (40); H→L+3 (40)	π→ π∗
4				214	0.24	16300	–	–	–	H→L+1 (75)	π→ π∗
5		251	12750	250	0.26	17400	–	–	–	H-1→L (90)	π→ π∗
6		324	4760	318	0.11	7200	–	–	–	H→L (96)	n→ π∗
7	3 (55/45)	230	15800	225	0.30	20000	224	0.29	19500	H-1→L+1 (92/86)	π→ π∗
8		275	13400	253	0.27	18200	258	0.26	17500	H-1→L (96/97)	n→ π∗

^aPeak maxima were determined using a second derivative-based method.

^bTD-B3LYP 6-31+G(d,p).

^cH-highest occupied MO (HOMO), L-lowest unoccupied MO (LUMO).