The effect of bulky groups on the electro-optic coefficient r33r33 of a pyridine-donor nonlinear optical chromophore

• The effect of chromophore shape control on r33r33 was investigated.
• The measured r33r33 was found to be one third that expected.
• A method of estimating aggregation from absorption spectra was developed.
• Shape control by bulky group attachment benefitted neither r33r33 nor aggregation.
• Chromophore aggregation was found to be sufficient to explain the low measured r33r33.

The effect of bulky groups attached to pyridine-donor chromophores on the electro-optic coefficient r33r33 of host-guest polymers was measured by modulation ellipsometry. Overall, the experimental results indicated no significant beneficial effect of the bulky groups on r33r33. The maximum r33r33 achieved was just under 6 pm/V for the plain chromophore, compared with the expected 20 pm/V based on the molecular properties. Decomposition of the chromophore absorption band revealed significant aggregation, with the monomer fraction estimated to be marginally less than 1/31/3 for all chromophores studied. We attribute the lower achieved r33r33 values to increased molecular aggregation.