upon cation addition. In contrast to the g lum factors, the g abs values measured on the
first Cotton effect are in the range |10
À3 |–|10
À4 |.
12.2.4 Solid State Excimer CPL from Pyrene-Based
Molecules
Some pyrene-based molecules display CPL activity even in solid state, both in bulk
(as powders) or in polymeric matrix-based films. In these cases, a contribution of not
only intra- but also intermolecular excimers may be present. For example, the
already cited compound pyr-17 displays excimer associated CPL in polymethyl
methacrylate matrix (g lum ¼ |3.6 Â 10
À4 |), even though with a g lum factor around
half the one in solution and with sign inverted [20].
Intense excimer CPL was recently reported by Takaishi and Ema in
quaternaphthyl structures bearing 6 or 8 pyrene moieties (pyr-30 and pyr-31,
Fig. 12.6) [30]. They showed that at least 6 pyrene units were necessary to achieve
a rigid helical structure with skewed-arranged pyrenes (see DFT optimized structure
in Fig. 12.6). In fact, for pyr-30 and pyr-31, g lum values equal to |3.7 Â 10
À2 | and |
3.4 Â 10
À2 | were recorded in CH 2 Cl 2 (10
À6
–10
À5 M). One order of magnitude lower
g abs values was recorded for the first Cotton effect (g abs ¼ |4.8 Â 10
À3 | for pyr-31) in
the ECD spectrum. Importantly, weaker but still relatively intense CPL emissions,
g lum |5.3 Â 10
À3 | and |5.6 Â 10
À3 |, respectively, were detected for the same
molecules in solid state, as potassium bromide (KBr) pellet. It is worth mentioning
that in the present example, solid state recorded g lum values are 6–7 times lower than
in solution.
Fig. 12.6 Pyrene-decorated quaternaphthyl structures reported by Takaishi and Ema, and DFT
optimized structure of pyr-31. Reproduced from reference [30] with permission from The Royal
Society of Chemistry
12 Circularly Polarized Luminescence from Intramolecular Excimers
285
first Cotton effect are in the range |10
À3 |–|10
À4 |.
12.2.4 Solid State Excimer CPL from Pyrene-Based
Molecules
Some pyrene-based molecules display CPL activity even in solid state, both in bulk
(as powders) or in polymeric matrix-based films. In these cases, a contribution of not
only intra- but also intermolecular excimers may be present. For example, the
already cited compound pyr-17 displays excimer associated CPL in polymethyl
methacrylate matrix (g lum ¼ |3.6 Â 10
À4 |), even though with a g lum factor around
half the one in solution and with sign inverted [20].
Intense excimer CPL was recently reported by Takaishi and Ema in
quaternaphthyl structures bearing 6 or 8 pyrene moieties (pyr-30 and pyr-31,
Fig. 12.6) [30]. They showed that at least 6 pyrene units were necessary to achieve
a rigid helical structure with skewed-arranged pyrenes (see DFT optimized structure
in Fig. 12.6). In fact, for pyr-30 and pyr-31, g lum values equal to |3.7 Â 10
À2 | and |
3.4 Â 10
À2 | were recorded in CH 2 Cl 2 (10
À6
–10
À5 M). One order of magnitude lower
g abs values was recorded for the first Cotton effect (g abs ¼ |4.8 Â 10
À3 | for pyr-31) in
the ECD spectrum. Importantly, weaker but still relatively intense CPL emissions,
g lum |5.3 Â 10
À3 | and |5.6 Â 10
À3 |, respectively, were detected for the same
molecules in solid state, as potassium bromide (KBr) pellet. It is worth mentioning
that in the present example, solid state recorded g lum values are 6–7 times lower than
in solution.
Fig. 12.6 Pyrene-decorated quaternaphthyl structures reported by Takaishi and Ema, and DFT
optimized structure of pyr-31. Reproduced from reference [30] with permission from The Royal
Society of Chemistry
12 Circularly Polarized Luminescence from Intramolecular Excimers
285