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.