Table 1.

Photophysical and electrochemical parameters related to singlet state photoinduced cleavage and sensitization ability of tetrafluoroborate salts of N-alkoxyheterocycles in acetonitrile at room temperature.

Structure		λmax* (nm)	1E*0,0† (kcal mol−1)	λ+max‡ (nm)	ε+max§ (M−1 cm−1)	k+e|| (stilbene) (M−1 s−1)	Φions¶	Φradical#	Eox** (V vs. SCE)	t††(μs)
	1	315	80.1	610	1650	2.0 × 1010	0.48 ± 0.08	0.43 ± 0.06	2.1	3
	2	334	80.4	670	2135	1.9 × 1010	0.50 ± 0.10	0.39 ± 0.07	2.1	3
	3	322	75.0	695	15 100	1.9 × 1010	0.53 ± 0.09	0.43 ± 0.12	2.0	2.5
	4	345	78.8	475	36 000	1.4 × 1010	0.08 ± 0.04	–	1.8	44
	5	379	69.2	460	15 000	–‡‡	0.07 ± 0.04	–	1.4	–

^*Absorption maximum of the first absorption band of the N-methoxyheterocycle;

^†Energy of the excited singlet state of the corresponding N-ethyl structures (1E–5E), determined as the midenergy point of the absorption and fluorescence spectrum, see text;

^‡Absorption maximum of the radical cation;

^§Extinction coefficient at the absorption maximum of the radical cation. Estimated errors are ±10% for 1–3, and ± 20% for 4 and 5;

^||Bimolecular rate constant for oxidation of stilbene by the radical cations. The experimental errors are ca 10%;

^¶Quantum yield of formation of separated radical cations, determined as described in the text using trapping with stilbene, errors derived from multiple measurements;

^#Quantum yield of formation of separated methoxy radicals, determined as described in the text using trapping with diphenylmethanol, errors derived from multiple measurements;

^**Estimated oxidation potential of the neutral heterocycle, determined by adding 0.25 V to the oxidation potential of the corresponding hydrocarbon (46), using 1.80 V for naphthalene (55), 1.73 V for phenanthrene (56), 1.57 for trans-stilbene (56) and 1.15 V for trans-4-methoxystilbene (57), all versus SCE;

^††Approximate lifetimes of the radical cations under the experimental conditions in acetonitrile at room temperature;

^‡‡Oxidation of stilbene is too slow in this case.