Dallapiccola is rightly recognized as one of the most important Italian composers of the twentieth century. His interest in dodecaphony was initially kindled from the closing chapters of Schoenberg's Harmonielehre ("Quarten-Akkorde"). The 1930s were then devoted to cautious searching and experimentation and led to the triptych Liriche greche in 1945, which represents a decisive compositional turning point. This work also brought Dallapiccola in contact with René Leibowitz, whose constructive criticism deepened Dallapiccola's understanding of twelve-tone technique, yet also incited in him resistance. The chord of an ascending diminished fifth followed by a perfect fourth was to become the "accordo fondamentale" of Dallapiccola's music, as notably demonstrated in Ulisse (1968), his only full-scale opera.
Kämper, Dietrich (2015) "Verso la sensibilità, non verso la teoria": Luigi Dallapiccolas Weg zur Zwölftontechnik. In: Archiv für Musikwissenschaft, Vol. 72, No. 4, pp. 262-276. Available at https://openmusiclibrary.org/article/47045/.