ABSTRACT
Optical response from organic molecules is determined by the interplay between electronic and vibronic excitations that is well understood and addressed in different text books and monographs. This chapter provides overview optical properties of molecular aggregates, molecular crystals, and molecular-solid systems focusing on specific features related to the nanostructures. Optical properties of organic molecules are modified due to their aggregation in molecular complexes that has been observed in a number of molecular systems. The use of dyes in nanophotonic devices, in dye lasers, and various photoinduced reactions caused extensive studies of their electronic and optical properties. The modifications of the optical absorption spectrum with concentration were interpreted as the formation of molecular aggregates. The linear and nonlinear optical properties of organic nanofibres can be controlled by appropriate choice of the functional groups. The optical properties of nano-structured systems are governed by both the intrinsic properties of the nano-structures and their interactions with the matrix.
