Patent ID: 8383931

Claim:
A substrate, characterized in that it is coated with a film comprising at least one compound of formula (I) below: in which: Xa and Xb, which may be identical or different, are chosen from N, P, O, S, Se and Te atoms, R 1 , R 2 , R 3 and R 4 , which may be identical or different, represent a group chosen from aryl and heteroaryl rings containing 4 to 10 carbon atoms, said aryl or heteroaryl rings possibly being substituted with one or more halogen atoms, hydroxyl groups —OH, alkyls containing 1 to 30 carbon atoms, alkoxy —OC n H 2n+1 or ester —C(O)OC n H 2n+1 , in which 0≦n≦16, the compound of formula (I) being present in said film in the form of spherical-like particles with a diameter of less than or equal to 300 nm.