Semiconducting nanoparticles are heterogeneous systems that lack long-range three-dimensional crystalline order and have large inorganic-organic interfaces that exert important influences on their size-dependent properties. While it is well established that small particles or surface layers often possess different properties from bulk solids, much remains unknown with respect to specific compositional or nanostructural origins of such differences in surfactant-passivated nanoparticle systems. In the case of hexadecylamine-coated InGaP nanoparticles, information about molecular-level compositions and structures can in principle be obtained by a combination of solid-state ⁷¹Ga, ¹¹⁵In, ¹H, and ³¹P NMR measurements, which can be subsequently correlated with nanoparticle optical properties. In practice, however, molecular NMR measurements are often at the limits of technical feasibility, because of challenges presented by the absence of long-range order, low-signal sensitivity, complicated heterogeneous structures, and/or quadrupolar interactions. Nevertheless, such considerations can often be mitigated by using powerful double-resonance, multidimensional, and/or very high field NMR techniques. Recent results and new insights will be discussed concerning the molecular compositions and structures of distorted surface environments in InGaP nanoparticles, their modification, and their influences on InGaP optical properties. These will include first-ever molecular results obtained for semiconducting nanoparticles at 20 Tesla acquired at the National High Magnetic Field Laboratory spectroscopy facilities in Tallahassee, FL. In particular, greatly enhanced macroscopic photoluminescence quantum efficiencies are shown to result after surface etching treatments of InGaP nanoparticles in hydrofluoric acid, which affect the composition and extent of ordering at the nanoparticle surfaces. These insights are being used to understand and optimize the effects of different synthesis and processing conditions on the compositions, structures and properties of semiconducting nanoparticles for different device applications.