Table 2.

Spectral, kinetic and energetic properties of N-methoxy and N-ethylheterocycle excited triplet states in acetonitrile at room temperature.

Structure*		3λ*max† (nm)	3kq*(O2)‡ (M−1 s−1)	3E*0,0§ (kcal mol−1)	Ered|| (V vs. SCE)	3Ered*¶(V vs. SCE)	3t*# (ns)
	6	700	6.2 × 108	67.2	−0.53	2.4	80
	6E	700	7.8 × 108	67.2	−0.67**	2.2	50
	7	550	1.1 × 109	56.5	−0.65	1.8	600
	7E	550	1.0 × 109	56.5	−0.79	1.7	500
	8	525	1.8 × 109	57.2	−0.63	1.9	400
	8E	525	1.2 × 109	58.1	−0.77	1.7	400
	3E	500	4.5 × 108	60.3	−0.96††	1.7	1000
	1	440 (500)‡‡	5.3 × 108	–	−0.84	–	2700
	1E§§	(440) 500‡‡	6.0 × 108	60.4§§	−0.98||||	1.6	1900

^*Experiments performed using tetrafluoroborate or hexafluorophosphate salts except where noted;

^†Absorption maximum of the excited triplet state;

^‡Bimolecular rate constant for quenching of the excited triplet by oxygen;

^§Energy of the 0,0 phosphorescence transition measured in EPA or ethanol/methanol/methyl iodide glass at 77 K;

^||Estimated reduction potential of the N-methoxy or N-ethylheterocycle versus SCE, from measurements as part of this work or as indicated. The reduction potentials of the N-methoxy structures were not measured but are obtained by adding 0.15 V to those for the corresponding N-ethyl structure, as described in Ref. (37);

^¶Reduction potential of the excited triplet state estimated as E_red* = E_red + (3E*_0,0/23.06);

^#Measured lifetime of the excited triplet state;

^**from Ref. (64);

^††from Ref. (65);

^‡‡Two maxima observed, the weaker absorbance is in parenthesis;

^§§Iodide salt;

^||||From Ref. (66).