The relation between cofacial interpolymer distance and solid-state photophysics of random hydrophilic (Me, iso-Pr, isopentyl)- and hexadecyloxy hydrophobic-substituted poly(p-phenylene ethynylene)s was studied. The side chain bulk influences the packing of the polymers at the air-water interface, by providing greater polymer-polymer spacing. Interchain distance has a strong influence on the spectral properties of PPEs. Thin films were prepd. on glass substrates by drop casting, by spin casting, and by using the Langmuir-Schaefer (LS) method. Normalized UV-vis and PL spectra of the isopropyl-substituted PPV films spin cast, drop, and soln. are similar, illustrating the lack of order in the spin cast film relative to the LS film. However, the drop cast film has a PL max. at 463 nm arising from non-aggregated polymer chains, along with three other red-shifted peaks at 494, 512, and 553 nm which may arise from multiple aggregated states, indicating that the drop cast film is intermediate between the LS (fully aggregated case) and the spin cast (least aggregated state). [on SciFinder(R)]