| Summary: | Fluorescence from dialkylamino donor–acyl acceptor substituted 1,8-naphthalene derivatives can occur either from a planar (PICT) or a twisted (TICT) intramolecular charge transfer excited state. The photophysical properties of 8-acetyl-1-(dimethyl-amino)naphthalene (<b>3</b>) and 8-pivaloyl-1-(dimethyl-amino)naphthalene (<b>4</b>) are compared with 1-methyl-2,3-dihydronaphtho[1,8-bc]azepin-4(1H)-one (<b>5</b>). In <b>3</b> and <b>4</b>, both the carbonyl and amino groups are forced to twist out of the plane of the naphthalene ring. In <b>5</b>, these groups are nearly coplanar with the naphthalene. Neither <b>3</b> nor <b>4</b> fluoresce as strongly as <b>5</b>, but all three show similar degrees of solvato-chromism and all are strongly quenched by alcohol solvents. Nitrile <b>6</b>, 8-cyano-1-(dimethyl-amino)naphthalene, does not show the same degree of solvato-chromism as <b>3</b>–<b>5</b>, nor is it as affected by alcohols. Calculations corroborate the experimental results, indicating that <b>3</b>–<b>5</b> emit from a PICT excited state.
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