Novel liquid crystalline (LC) hyperbranched (HB) polyesters comprising phenylbenzothiazole (PBT) unit as mesogen in the interiors were prepared at various feed mole ratios (A(2)/B-3) by solution polycondensation of a dioxydiundecanol derivative of PBT (A(2) monomer) with trimesic acid trimethyl ester (HB monomer) via A(2)+B-3 approach and their LC and optical properties were investigated. Analogous linear polyesters containing the PBT unit in the main chains were also prepared by the solution polycondensation of A(2) monomer with aromatic or aliphatic dimethyl esters. FTIR and H-1-NMR spectroscopies indicated that the HB polyesters are produced without gelation during the polycondensation and have degree of branching (DB) of 7-46%. The structures of HB polymers changed depending on the feed mole ratios and the polymer prepared in the mole ratio of A(2)/B-3 = 3/2 had the highest inherent viscosity and DB. Acetylation of terminal OH group-having HB polyesters prepared in excess mole ratios of A(2)/B-3 afforded ones bearing acetoxy groups in the terminals. DSC measurements, polarizing microscope observations of textures, and X-ray analyses suggested that only the terminal OH group-having HB polymer prepared in the mole ratio of A(2)/B-3 = 3/1 form smectic C phase. In the linear polymers, the polymers derived by using the aromatic dimethyl esters had no LC melt, but those from the aliphatic dimethyl esters formed LC smectic C phase. The acetoxy group-bearing HB polymers showed more stable smectic A or C phase than those with the OH terminals. Solution UV-vis and photoluminescent (PL). spectra indicated that the linear and the HB polymers have analogous optical properties and display maximum absorbances and blue-light emission on the basis of the PBT unit, where the Stokes shifts were observed because of intermolecular aggregation effects, but there is a large difference between the optical behaviors of the linear and the HB polymers in film, whose E-g values of the linear polymers decreased and those of the HB polymers vice versa. Quantum efficiencies (Phi) had a tendency of increase in the linear polymers and the HB polymers forming LC phases. (c) 2008 Wiley Periodicals, Inc.