Observation of Size‐Dependent Optical Properties Based on Surface and Quantum Effects in Nanocrystals of 5,5′‐Bis(4‐Biphenylyl)‐2,2′‐Bithiophene

Herein, 5,5′‐bis(4‐biphenylyl)‐2,2′‐bithiophene (BP2T or PPTTPP) nanocrystals are prepared via a modified miniemulsion technique. X‐ray diffraction and selected area electron analyses reveal that the BP2T molecules stand almost upright against crystal basal plane. With decreasing nanocrystal size, peak energies of photoluminescence (PL) spectra blue‐shifted in photon energy range from bulk to monomer state. Energy‐wavevector dispersion plots reproduced using data size‐dependent PL indicate size dependence optical properties cannot be explained by conventional quantum confinement effect used inorganic nanocrystals. The micro‐PL time‐resolved measurements can attributed combined based on surface effects as well lattice softening, involving specific area‐dependent site shift exciton confinement. Moreover, amplified spontaneous emission is observed ≈600–1000 nm which smaller than previously reported for organic systems.